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Famous Mineral Localities: The Bristol copper mine Connecticut.

The Bristol mine in Connecticut has produced world-class specimens of crystallized chalcocite and bornite, fine examples of which are held in major museums and private collections around the world. Although production of the best specimens was limited to a few years in the late 1840's, the history of intermittent copper mining at Bristol covers 150 years, not ceasing permanently until 1953.


The Bristol Copper mine is located near the city of Bristol, in Hartford County, north-central Connecticut. After some tentative beginnings, commercial mining began here in 1837, and ended in 1857; apparently, all of the fine chalcocite and bornite specimens now extant were found during this phase, especially during the late 1840's. A second major period of mining, during which very rich ore was struck, commenced in 1888, but economic difficulties and mismanagement of the mine forced closure in 1895. In 1946, some exploratory work led to partial dewatering of the mine and attempts to exploit remaining ore reserves, but the fall of copper prices from their World War II levels forced the mine to close for a third and certainly final time in 1953. (The main shaft is now filled with junk cars.)

The superbly crystallized Bristol chalcocite specimens (along with a much smaller number of equally fine bornite specimens) found during the 1837-1857 period rival the famous Cornwall, England, specimens for crystal size and quality. During this period, Bristol was the most important copper mine in the United States, preceding the great Michigan, Montana and Arizona copper bonanzas.

The Bristol orebody is scientifically important in the evolution of ideas about ore formation; Bateman (1923) used it to demonstrate for the first time that chalcocite could occur as a primary hypogene mineral. Until his work was published, it had been assumed that chalcocite was always a product of supergene enrichment in copper deposits.

Bristol offers much of historical interest as well. The mine property was originally owned by the Yale family, after whom Yale University is named. During the period of major development in the mid-l9th century, several prominent Yale people were involved in the ownership and operation of the mine. These included Benjamin Silliman Sr. and Jr., James Dana Whitney, and John M. Woolsey. The English-born Charles M. Wheatley of New York, later to manage and give his name to the famous Wheatley lead mines at Phoenixville, Pennsylvania, came on as manager of the Bristol mine just as the great chalcocite and bornite specimens were about to be discovered. Wheatley, Whitney and Benjamin Silliman Jr. all protested vehemently against the mine owners wishes to process fine crystal specimens as ore, and are no doubt responsible for the preservation of most of the best specimens that have survived.


The Earliest Phases of Mining

The discovery of the copper deposit at Bristol originated in the determination of John Winthrop, Jr., first Governor of the colony of Connecticut, to explore his territories for mineral resources. In 1651, Winthrop was granted automatic permanent ownership of any ore deposits he located, plus any timber and water resources within three miles of his mines. Connecticut colonists everywhere were soon searching for secondary mineralization that would betray the presence of metals. Connecticut's first copper mine was begun at Simsbury in 1709, and operated for the next 70 years; it was also put to use during the Revolution as a prison for captured British soldiers. Today the mine area, known as "Simsbury Mine and Newgate Prison," near East Granby, is a Connecticut Historic Site and popular tourist attraction.

There is some archaeological evidence to suggest that the Bristol copper deposit was worked by Native Americans long before English colonization. In 1798 a local farmer named Theophilus Botsford investigated a spring of greenish water issuing from a spot beside an old Indian trail at the base of Zack's Mountain, a small hill near Bristol. The water was killing nearby vegetation, and Botsford correctly assumed there was copper in the spring water. With a yoke of oxen he plowed away some of the ground near the spring, and discovered a vein of copper ore. He did not, however, follow up on the discovery (Hurlbert, 1897).

In 1800, Asa Hooker, operator of a Bristol brass foundry, obtained a lease on the property from Sarah Yale, the widow of Abel Yale, descendent of Elihu Yale, founder of Yale University (Beals, 1954). Hooker turned the lease over to Luke Gridley, a local blacksmith and fence inspector, who promised Sarah Yale a one-thirtieth share of the ore or any other valuable "treasure" that might he found. Gridley worked the outcrop for eight years with hand tools, extracting small amounts of ore which he smelted in his nearby forge. This product was probably turned over to Hooker for use in his foundry business (Harte, 1944). But Gridley died in 1810, and the property lay dormant for the next 26 years.

Major Development, 1836-1846

In 1836 the Bristol brass industry was growing fast, and George Bartholomew, associate of E. N. Welch, owner of the Welch Foundry, obtained a 15-year lease on the Bristol property from Abel Yale, Jr., son of Sarah Yale, the new managers promising Abel one-twelfth share of the proceeds from mining. For two decades the copper mine undoubtedly played a major role in the early development of Bristol's industries such as the Bristol Brass Company and two major clock manufactories for which Bristol gained fame; all these came under the control of Welch (Hurlbert, 1897).

When Bartholomew obtained the property he immediately trenched it to determine its values, opening an area measuring 10 by 20 feet and 17 feet deep. Beals (1954) describes what this trenching exposed: "The variegated copper vein, copper, sulfur, iron and silver ore between granite and sandstone was so rich, about 70% copper content, it needed only to be trimmed with a hammer to go into the smelter furnace." The term "variegated copper" referred to bornite ([Cu.sub.5][FeS.sub.4]).

Ores from this early operation were shipped overseas--probably to Swansea, Wales--for processing. There is evidence of smelter slag on the shores of New Haven harbor but no evidence has been found to connect it with the Bristol mine. That the property showed a profit is a tribute to the richness of the ore values mined.

Bartholomew was persuaded by several local businessmen to raise investment funds and establish the first Bristol Mining Company. When the company was incorporated by the Connecticut State Legislature on December 7, 1837, it had a capitalization of $60,000, raised by the sale of 2400 shares at $25 each. The original partners were Bartholomew, Bristol clockmakers Erastus and Harvey Case and Sylvester Willard, and Andrew Miller, "a capitalist and practical miner" from Fleming, New Jersey (Domonell, 1991). Miller, who held 1200 shares, was president of the company. Intense activity to develop the mine then got under way. A large adjoining tract of land was leased and buildings erected, miners were hired, and a dam was built to impound the waters of Poland Creek for power. A main shaft was begun, and at 60 feet the first crosscut was put in to intersect the vein. A 4-foot ore zone was located only 13 feet from the shaft. A deeper crosscut proved the vein to be 10 feet wide further down (Clouette and Roth, 1984).

In 1837 the mine was visited by Connecticut state geologist Charles Upham Shepard, who described the deposit briefly and with little enthusiasm, saying "vitreous copper occurs in small quantity in the Bristol Copper Mine intimately associated with variegated copper." Shepard's report gives no indication that at this time he saw any crystallized specimens of chalcocite ("vitreous copper") or bornite ("variegated copper"). By 1839 Benjamin Silliman, Sr., had visited the property and had written a much more enthusiastic report, though likewise without mention of good crystals.

Andrew Miller, with his controlling interest in The Bristol Mining Company, apparently was a competent and financially responsible mine manager until his death in 1846. But Miller sold half of his interest for $28,000 to a group of English investors: Lawson Ives, Chauncey Ives, and Almon Farrell. Soon thereafter, the ore was shipped to England for smelting, at excessive cost. Miller made new arrangements with local farmers to haul the ore to Plainville, Connecticut, from whence it was taken via the Farmington Canal to a smelter at East Haven, and the copper taken from there to the Tyson copperworks at Baltimore, Maryland.

Miller brought in skilled miners from Cornwall, England--the famous "Cousin Jacks"--to increase the efficiency of the operation. These miners reportedly found the Bristol orebody to be reminiscent of those at Truro, Redruth and Penzance, Cornwall. In the late 1840's the "Cousin Jacks" would be on hand for the discovery of vugs lined with crystallized chalcocite, and may have troubled to preserve many specimens. Dr. Steven Chamberlain of Syracuse, New York, has reported that when he visited numerous private collections in Cornwall, England, over a hundred years later, "he observed, unexpectedly, a number of fine Bristol chalcocites which had been assigned a Cornwall pedigree," apparently brought or sent home by Cornish miners (Heitner and Lininger, 1997).

During the months just before Andrew Miller's death, there was apparently friction between him and his English partners; the annual reports for 1843 and 1845, prepared by Chauncey Ives, were not signed by Miller. When Miller unfortunately drowned in the Tunxis River early in 1846, Lawson Ives became the mine manager, and the financial situation deteriorated. A number of lawsuits were filed successfully against the company, and in 1846 the first Bristol Mining Company collapsed.

The Peak Period, 1847-1857

In 1847 an opportunistic New York investor, Richard F. Blydenburgh, negotiated a long-term lease on the Bristol property with Abel Yale, then sold two-thirds of his interest to another New Yorker, Hezekiah Bradford, for $61,849. Dr. Eliphalet Nott, the president of Union College in Schenectady, New York, then mortgaged the property from Blydenburgh and Bradford. By 1851, Nott had bought up the other interests and become sole owner of the mine's lease, appointing himself president of the second Bristol Mining Company (Hislop, 1971). Major stockholders included Yale people such as John M. Woolsey, Josiah D. Whitney, and Professor Benjamin Silliman, Jr.--son of Benjamin Silliman, Sr., the great mineralogist who "almost single-handedly took Yale into pre-eminence in early American education in chemistry, geology and mineralogy" (Moore, 1999). This connection with the Sillimans of Yale would prove fortuitous for Bristol and its great mineral specimens.

The position of mine manager went to 24-year-old Charles Moore Wheatley. Although already a successful businessman, Wheatley had only an amateur naturalist's interest in geology and mineralogy, and no experience in mine management. However, his quick intelligence, enthusiasm, hard work, and dedication to mineralogy soon won him the support and respect of Benjamin Silliman, Jr. The warm relationship would pay continuing dividends for the Peabody Collection at Yale when Wheatley later took charge of the lead mines at Phoenixville, Pennsylvania, which now bear his name, and sent many fine specimens from there to Silliman in New Haven. Unfortunately, his tenure at Bristol lasted only until 1849, when he left to work at the Perkiomen and Ecton mines in Pennsylvania (Evans, 1984).

Under the leadership of its new cadre, the Bristol mine flourished, and soon was rated the most important copper mine in the northeastern United States (Smith and Smith, 1907). Some of the miners, still resenting the earlier management, and knowing of Wheatley's inexperience, distrusted the new mine manager, but Wheatley won them over by working underground with them in a friendly way and learning all he could from them. He overcame another early crisis in the form of the first labor strike at the mine, this by Irish miners who asked for, and were refused, time off with pay to attend Mass in New Britain. Some angry miners threatened the young manager, and several even devised a plot to lure him into the mine and kill him, but Wheatley ended the strike by arranging to have Father Luke Daly come from New Britain to say Mass at the mine. It is interesting to note that the strikers were receiving only 70 cents an hour when they went on strike (Clouette and Roth, 1984).

With steam power now in place, Eliphalet Nott and his associates sank a second shaft of impressive size, 6 feet by 8 feet, eventually dropping 240 feet in depth. Crosscuts were put in, and ore valued at over $200,000 was recovered. This was selected ore averaging 33% copper, according to Bateman (1923). One main source of copper was the "flucan" (a Cornish term for a wide fault-gouge zone filled with decomposed mineral matter), described by Silliman and Whitney (1855) as a talco-micaceous slate that was completely disintegrated such that no blasting was required, as it ran easily. The second and more important source of ore was the vein system.

Many of the historically important specimens now in the Yale-Peabody collection certainly came to light at this time. A large number of fine chalcocite specimens also went to Union College, which is not surprising considering that Eliphalet Nott was president of that institution while also heading the Bristol Mining Company in the late 1840's. Many more fine chalcocites also went to Union College in 1858, when Charley Wheatley sold his collection to the school, Josiah Whitney having arranged the sale.

Heitner and Lininger (1997) provide a historical analysis of early collecting at Bristol; some of it necessarily is inferential and speculative, but it makes a fascinating account. They begin with the Third Edition of J. D. Dana's System of Mineralogy (1850), which contains the first mention of chalcocite in "large and brilliant crystallizations" from "a vein at Bristol, Conn." As Dana in 1844 had mentioned only a "fine vein" at Bristol, and Shepard in the same year had cited only "vitreous copper" in massive form from Connecticut (and crystals from Cornwall), it seems safe to assume that the first crystal vugs at Bristol were struck early during the second major start-up of the Bristol mine, between 1847 and 1850, the period for which assay figures show the richest ore being produced. In 1852, Shepard writes of "splendid crystallizations" which occurred at Bristol "a few years since, but of late this locality has wholly ceased to produce them." There is no extant description of the vugs themselves, but the m ining engineer Charles Richardson, who visited in February 1854, states that "where vugs occur, the ore is very rich."

No real evidence exists as to who found the vugs, or who first collected specimens from them. Charles M. Wheatley left no written account of these matters, as we might have expected him to; Heitner and Lininger (1997) attribute this to the fact that "he was probably too busy collecting." In a personal letter to John H. Redfield on August 30, 1847, Wheatley writes "... the only consolation I have for being in this wilderness is that twice a day I have brought up from our levels some very fine things.... Vitreous Copper, Very good copper! oh! oh! oh!!" And on November 17, 1847, am over head & ears in X2 copper and the way I will astonish the natives at the Lyceum about New Year will be a caution...." When Dana and Silliman came to the mine in July, 1848. Wheatley writes, they "feasted their eyes with X vitreous all day." and when Silliman left he took away with him enough specimens to cause Wheatley to complain to Redfield that "The confounded fellow came up with a mighty large basket!" In September 1848, Mr. W . Lettsom wrote from London to tell Wheatley that "Your Bristol copper glance is beautiful and I am really much indebted to you for them."

Some of the Yale specimens seem to have been sold to Silliman, shortly after someone collected them, by one Ludwig Stadtmuller, a Bavarian immigrant and graduate of Yale's Sheffield Scientific School. Stadtmuller worked as an assayer at the mine during this period, and later became a mineral dealer in New Haven. Silliman may also have personally collected more specimens when he went with George Jarvis Brush and some Yale students on a field trip to the mine in 1849.

Of fine chalcocite specimens retained in Bristol, Smith and Smith (1907) gives a glimpse by quoting from a history of the Bristol school district written by Mrs. H. S. Bartholomew, daughter-in-law of the George Bartholomew who had worked the mine in the 1830's: "For many years after the 'Mine' was in operation or worked the ancient Culver house stood on its grounds surrounded by huge piles of waste material (tailings). Sometimes its windows revealed to outsiders a row of extra fine specimens of copper and quartz crystals, with some silver." Note here that in researching this article only one specimen showing native silver was seen (in the Smithsonian collection).

The 1850's saw a major disagreement among the owners and managers of the mine about what to do with the fine crystal specimens being found. Most of the owners wanted the specimens simply sent to the stamp mill to increase the yield, but Silliman (?) objected strongly. Hurlbert (1897), describing the management of the mine during 1855-1857, writes "It was during this administration that specimens of chalcocite of peculiar form could have been easily sold as cabinet specimens for hundreds of dollars, [but] were crushed for ore in spite of the protest of the mineralogist." Heitner and Lininger (1997) speculate that this "mineralogist" was Benjamin Silliman, Jr., or possibly Josiah Whitney or Ludwig Stadtmuller. It was perhaps in part to protest the fate of these specimens that Silliman and Whitney sold out their holdings at the same time as did Nott--in 1857. Their reason also may have been the financial extravagance of Henry R. Sheldon, hired in 1851 as mine manager and bringing with him a Cornishman, Captain W illiams, to oversee the property and production.

The period 1851-1857 proved to be a troubled one. Sheldon, having declared his intention to ensure large profits by holding down expenses, nevertheless spent money wildly on sinking another main shaft, constructing large buildings, and trying a costly experiment with an unorthodox ore separator that cost more than $10,000 (Heitner and Lininger, 1997). The pattern of extravagant spending kept the mine running deficits, despite raising large amounts of rich ore.

One problem not of Sheldon's making that arose in the early 1850's was a serious flood of groundwater trapping many miners at the face. Fortunately, they escaped without loss of life. This flooding required much clean-out work and created a need to secure the ground before mining could resume (Hurlbert, 1897). It should be noted that in spite of this event a report in the 1855 Mining Magazine stated that this was not a wet mine!

Silliman became more directly involved at this time in the management of the mine where, despite the best of intentions, he only reinforced Sheldon's improvidence. "The Professor [was] a fine theorist but a very poor practical miner. Hundreds of thousands of dollars, from first to last, were poured into the mine" (Norton 1872). For example, Sheldon and Silliman wasted much money in trying to replace steam with water as a source of power for the mine. To produce water power, a $30,000 dam was built half a mile from the mine, a sluiceway constructed, and a 38-foot water wheel installed; steam as a source of power was removed (Richardson, 1854). Nott took strong issue with Silliman over the installation of the water wheel. In a letter dated Jan. 2, 1855 he wrote, "I am not surprised at the delay in getting the works in order at the mine. You are aware, I presume, that in England the opinion changed in relation to the gain of power using high steam, also the improvement made in the generation in steam by Mr. Pond at the works of Hartford and New London Machine Shop. If you have not been aware of these facts you will, perhaps, inform yourself more fully." Clearly, this was Nott's polite way of saying that Silliman had made an incompetent decision to use water for power. When, indeed, the expensive dam later broke, flooding the surrounding area (Hurlbert, 1897), it was decided to return to steam power, but to fuel the steam boilers with peat mined nearby. The cost of this mining, and of the ovens which needed to be constructed to dry the peat, meant a total cost "several times as much as [for] an equal amount of any other fuel" (Heitner and Lininger, 1997).

Sheldon's personal extravagance also worsened the situation:

The company's agent ... kept eight or ten fast horses at his stables in Farmington and others at the mine. ... Once a dance was given in the storeroom which had been provided with steam pipes for heating it on this occasion as it was winter. Sibley's Band of Hartford, the best in the state at that time, was hired for $100. The supper was a costly one, wine of several kinds being furnished. That this wine was not an imitation may be inferred from the fact that those at the supper table amused themselves by throwing turkeys and chickens at each other. (Hurlbert, 1897)

By 1855, Whitney and a presumably wiser Silliman were suggesting ways to get the mine's finances back under control. They saw to it that a new shaft was sunk in the best place to exploit more fully the ores in the flucan; when these ores were processed in the Bradford ore separator (earlier put in place) the mine briefly turned profits of $1800/month. But nothing, in the longer term, could reverse the effects of the extravagance of the mine manager. When Silliman, Whitney and Nott sold out their interests in 1857, financial disaster was clearly imminent. The rebuff of Silliman regarding the fate of the crystal specimens may have seemed to him merely a final, symbolic insult. James M. Woolsey became the primary owner, and the company "became bankrupt in 1857, the year of the financial crash. This was in spite of the fact that $2,000 a month above business expenses had been earned during the last six months of the company's existence" (Domonell, 1991).

With the shutting down of the mine in 1858 came the inevitable auction of equipment and supplies. The ore hopper suffered an ignominious fate. It was bought and inverted to become the roof of a chicken coop (Smith and Smith, 1907). The mine bell met a more noble end: it was bought by factory owner E. L. Dunbar, who installed it in the belfry of his spring factory on South Street, and rang it 99 times each night, as a curfew bell (Peck, 1932). When Dunbar died, the ringing of the bell was stopped, but the townspeople petitioned the new factory owners and the ringing was resumed at a more reasonable rate (Smith and Smith, 1907). The bell was shifted from place to place and finally, in the 1970's, became available to the town. Suggestions were solicited, and an officer of the Bristol Fire Department suggested that it be erected outside the main fire station as a memorial to those firefighters who had fallen in the line of duty to the town. The City Fathers obtained the bell and the memorial was constructed, but later it was discovered that no one in Bristol had ever died in the line of duty as a fireman. Ironically, the first fireman later to do so was the officer who had originally suggested the memorial (Bristol fire officials, personal communication).

Renewed Efforts, 1888-1895

The coming of electric lighting in the 1880's inspired a huge demand for copper, and a subsequent rise in copper prices. Consequently, many old American copper mines, including the Bristol mine, drew new interest from speculators. Burton Cowles, a former Bristol resident and later the proprietor of a wood engraving company in Pittsfield, Massachusetts (Heitner and Lininger, 1997), had an idea for using iron to extract copper from mine solutions at Bristol. Cowles experimented with samples from the mine tailings dump, using acid to leach the material; the dissolved copper was deposited on scrap iron. Cowles claimed that $300,000 worth of copper could be won in this way from the existing mine dumps, and although the Waterbury American newspaper (May 10, 1888) opined that he was "practicing transmutations while romancing the public," Cowles was indeed able to raise enough capital to re-open the mine. In 1888, he and Edgar G. Hubbell, librarian and curator of the Pittsfield Athenaeum, raised some $500,000 in inve stment capital and acquired title to the mine, plus its surrounding tract of 120 acres, from the estate of John W. Woolsey. During the spring and summer of 1888, Cowles and three hired laborers worked hard enough to be able to recover 35 pounds of pure copper daily from the old dumps; the local newspapers began to speak more favorably of the project, and "copper fever once again returned to Bristol" (Heitner and Lininger, 1997).

Soon Cowles turned his attention from the dumps to the underground workings. The old Williams shaft was dewatered by round-the-clock pumping during the autumn of 1888, and excitement increased when some recovered ore samples were found to contain significant silver. On November 12, 1888, the new concern--optimistically named the Bristol Copper and Silver Mining Company--acquired all the property that Cowles and Hubbell had received from the Woolsey estate. The officers (and investors) in the company included William E. Tillotson, President; William E. Robertson, Vice-president; Edward S. Francis, Treasurer; Hubbell, Secretary and General Manager; and Cowles, mine foreman. The old Williams shaft (soon to be re-named the Tillotson shaft) was extended from its original 240 feet to 400 feet, a 40-foot-high hoisting house was built over it, and a new stamp mill was ordered. In January 1889 a large derrick and portable hoisting engine were added, the slumped open-cut was re-opened, and underground blasting was begu n on a crosscut at the 180-foot level. A Captain John Juliff, later called "Bill Silica," who had been an active miner in the West, was hired to assist Cowles as mine manager.

Newspapers at the time touted a new era of wealth and prosperity. They reported ore assaying at 73.41% copper, containing 23 ounces of silver per ton (Perry, 1975). In July 1890, the Bristol Herald reported that "a four-foot-wide body of yellow ore" had been encountered, and took the occasion to claim that the copper mines of Bristol were probably "the most profitable mines worked in the United States today"--this while Butte, Bingham, Bisbee and the Keweenaw Peninsula were working. Professor Silliman was quoted as saying that the ore veins extended from Bristol to Hamden, a distance of 25 miles at least. He also suggested that the mines would provide work for 30,000 people. Cowles meanwhile continued also to promote the value of working the mine tailings by his original acid-leaching method, and told the Southington Phoenix that the company expected to pay for this operation in full by the recovery of silver values from the mine.

Intensive mining between 1889 and 1891 continued to yield apparent good news, exaggerated by Cowles' public-relations efforts and newspaper "hype." Very rich veins of ore were struck on the newly re-opened surface workings, the 180-foot level, and the 285-foot level; this last vein yielded ore showing 74% copper and 17% silver. But an ominous note was struck in early 1890, when Charles M. Rolker, a consulting mining engineer and metallurgist, investigated the mine thoroughly and reported to Tillotson that the belief that "a vein increases in richness as it goes down" is "an hallucination," while at the same time, inevitably, mining costs increase with depth (Heitner and Lininger, 1997).

Surely, costs were increasing, and the management, like its predecessor in the 1850's, was spending recklessly. Rapidly climbing costs of pumping and ore recovery in the ever-deepening shaft, as well as a miners' strike and repair costs for broken equipment in the concentration plant, were by the early 1890's putting the company in debt. In September 1892, at the 400-foot level, the miners struck a mass of ore "so nearly pure as to admit of bending," but pumping for these depths had to proceed at a rate of 115 gallons per minute. Copper prices meanwhile were falling, and sales becoming anemic. And despite the fantasies of Cowles, Silliman and the local newspapers, the fact was that this was a fairly small orebody, now rapidly nearing the end of its exploitability. In July of 1893, Edward S. Francis, Treasurer of the company and a cashier for the Pittsfield National Bank, committed suicide; Hurlbert (1897) suggests that he did so because he had "defaulted his home trust" because of his heavy outlay of capital in the mine. Walter Cutting, who had succeeded Tillotson as company President, served to Edgar Hubbell legal papers which attached the mine, machinery and property of the company for $100,000, and the Connecticut courts awarded a judgment against the company, such that Cutting became sole owner on December 5, 1893. Cutting continued to operate the mine into 1894. Its death knell tolled in 1895, as a result of "a classic mining scam" (Heitner and Lininger, 1997) involving the alleged discovery of gold underground. A mining engineer known only as Major Allen was hired, having come highly recommended as a metallurgist and chemist (Domonell, 1991). To show his authority, he discharged several mine employees immediately. At a meeting with the board of directors, Allen confided that there was a body of very rich gold ore deep in the mine; he showed specimens of the ore, and urged that more investment be secured to enlarge the deeper workings downward and laterally. Money was borrowed--but management was suspicious enough to hire detectives, who found that Allen, under an assumed name, had had some mysterious wooden crates shipped in from the west to a freight station near Bristol. Then, of course, he had salted the mine with the "foreign" gold. Allen, his scam discovered, submitted his resignation, but not before Cutting had been swindled out of a large sum; afterwards, Cutting "never wanted to hear the name of the Bristol copper mine mentioned as long as he lived" (Domonell, 1991). This was the end of the Bristol mine in the late 19th century.

There is no record of crystal specimens being recovered during this phase of mining. Heitner and Lininger (1997) write that "a thorough search through the 15-year run of the Mineral Collector magazine revealed no new material on the market" from Bristol during the 1890's. Given the tendency of mine management and the local press to trumpet any good or interesting news from the Bristol mine at this time, it is reasonable to infer that no new chalcocite or bornite crystal specimens came to light.

Final Attempts, 1946-1953

For five decades the Bristol mine lay dormant, suffering deterioration and vandalism. Its only good moment during this time was the December 1922 visit of Yale geologist Alan M. Bateman, whose report in Economic Geology, entitled "Primary chalcocite: Bristol Copper Mine, Connecticut," expanded understanding of copper sulfide orebodies (see below).

The world wars had brought on copper shortages and high copper prices, and Allen Hearst of Forestville, Connecticut, convinced himself, both that there were still significant ore reserves in the Bristol mine, and that 20th-century technology could profitably extract copper even from low-grade ores at Bristol.

Hearst formed the Connecticut Mining and Milling Company with the express purpose of extracting silver and copper from the tailings on the site. He also undertook some limited dewatering and building. But the fall of world copper prices from their wartime highs finally saw to it that the venture was not successful; the mine was abandoned again in 1953. The property, zoned for industrial use, is now leased by a fuel oil company with a portion of the property used for a rubble dump and equipment storage site. The shafts have been filled and sealed, and access to the underground workings of the deposit will probably never again be possible.


The geology of Bristol is relatively straightforward. The ores occur largely along a major fault, the Bristol Fault, which forms the boundary between two major rock types, the Hartland Schist to the west and the Triassic-age red arkose of the Newark Formation to the east. The ores were found both within the fault system and as disseminated grains and blobs in selected sandstone beds of the arkose.

The Hartland Schist is a highly foliated rock consisting mainly of muscovite, quartz and garnet. It forms the footwall of the deposit, and its material forms the matrix of some specimens. Bateman (1923) reports the following accessory minerals in the schist: plagioclase, biotite, tourmaline, calcite, rutile, kyanite, chlorite and staurolite. Some of the collections viewed for this study revealed discrete garnet crystals in schist from this formation, but these were found outside the deposit. In addition, talc specimens labeled "Bristol" may well have come from outside the ore zones.

In earlier descriptions of the deposit, large "horses" of granite were reported in the ore zone (Silliman and Whitney, 1855). This study found no ore specimens confirmed as having granite attached. The inference is that the horses reported were actually blocks of sandstone from which the iron cementing agent had been leached: discrete crystals, particularly of chalcocite, are seen commonly on gray sandstone from Bristol. The horses are significant in that they created an environment conducive to deposition of ore sulfides, particularly in well-crystallized form. The leached sandstone will be discussed below, as the leaching process, according to Bateman (1923), played a significant role in the deposition of copper.

The Triassic arkose of the Connecticut River Valley, as well as occurrences in New Jersey and Pennsylvania, have been carefully studied and are well-known. The arkose belongs to the larger Newark Formation which crops out frequently in the Northeast, and has yielded some copper in several localities. At East and West Rocks, near New Haven, as well as elsewhere in the Valley, the arkose is overlain by later volcanics, which Bateman (1923) cites as the source of the copper-bearing solutions. Percival (1842) describes the arkose as a coarse sub-talcose granite--an example of the freedom with which the term "granite" was used in the early literature. The arkose consists of quartz and feldspar grains with some mica and chlorite, cemented with red iron oxide, a typical cementing agent of sedimentary rocks.

As already mentioned, copper ore was found in two modes: in rich masses and veins, sometimes with spectacular crystals of chalcocite and bornite, and in the so-called flucan, or fault gouge, filling. The vein system ranged from 6 inches to 3 feet in width, and tended to follow fractures parallel to the schist foliation (Richardson, 1854). Bateman (1923) reported solid copper sulfide on the wall rock of the footwall vein to a thickness of 8 inches and running 50% copper. Ore was also mined as disseminated grains and knobs and in pockets in the sandstone layers permeable to the ore-bearing solutions. The richest disseminated ore was that located closest to the vein system.

The original aqueous ore solutions were rich in copper and carbon dioxide; they also contained sulfur, silver, calcium, gold, lead and zinc (Bateman, 1923). Where they came into contact with the red sandstone, chemical reactions occurred. In comparing the red and gray sandstone arkose, Bateman (1923) found no significant differences save for the color; he concluded that the gray sandstone resulted when the red sandstone had its iron oxide cementing material leached away by the ore solutions. The iron was oxidized by the sulfur "in a continual and gradual manner" (Bateman, 1923), and this caused the solution to grade from cupric to cuprous as controlled by iron oxide availability. The gradual change resulted in the sequential deposition of copper sulfides ranging from chalcopyrite to bornite to chalcocite. Specimens reviewed for this study show the same overlapping sequences as reported by Bateman, with some apparently quite pure end-members being observed. Other specimens show one species replacing another; P osnjak et al. (1915) report extensively on this phenomenon. One exceptional example observed several times by this writer was of chalcopyrite in stalactitic form, sometimes a fine yellow, sometimes iridescent, with an inner core of a black mineral assumed to be bornite.

Bateman's study led him to the conclusion that the chalcocite at Bristol is a primary ore mineral. This was significant and important, as the assumption had been that all chalcocite found in copper orebodies was of secondary (supergene) origin. Finally, Bateman (1923) hypothesized that if enough iron oxide had been present to use up the sulfur completely, the ore solutions would have produced native copper much like that found elsewhere in the Newark Formation and in northern Michigan. It is fortunate indeed for the mineral collector that the chemical process stopped at the chalcocite stage, and that the "horses" were present to provide vuggy areas suitable for the deposition of crystals.


Azurite [Cu.sub.3][([CO.sub.3]).sub.2][(OH).sub.2]

Azurite was seen only as small blebs and coatings on a few specimens.

Barite [BaSO.sub.4]

The early literature of Bristol touts the superb barites found here, in some cases comparing them favorably with the classic spectacular blades once found at Cheshire, Connecticut. For example, Kemp (1906) refers to "unusually fine chalcocites and barites [which] made the mine famous the world over," and Shepard (1837) describes "white heavy spar in which are embedded perfect crystals of quartz." Examples of these latter specimens were seen during this study. However, fewer than ten Bristol barites were examined in all. Two habits were noted: white, bladed, opaque crystals forming sub-parallel, petal-like groupings; and transparent tabular crystals. None of these resembled the barites typical of Cheshire.

Two Union College specimens are quite attractive, with 2.5-cm white blades free-standing on mottled quartz points (#54), and a 5-cm sheaf of similar bladed barite crystals, again on mottled quartz points (#53). The color of the barite in both cases is a porcelaneous white. Three Yale specimens are also worthy of note. Specimen #1162 is similar to those at Union College save that the blades are smaller and more scattered, while Yale specimens C1156 and C1157 show the square tabular habit. Barite crystals on C1156 are colorless, measure 2 cm, and rest on matrix; crystals on C1157 are pale yellow, doubly terminated, and rest on quartz with minor chalcopyrite.

Bornite [Cu.sub.5][FeS.sub.4]

Bristol is recognized as one of the world's better sources of fine bornite crystals, though they were found there only rarely. Most bornite from Bristol is in the form of massive vein material in layers and stringers throughout the vein system, and as rounded blebs in white calcite or on quartz matrix. When crystallized, bornite shows the typical dodecahedron form (as in the recent very large, sharp crystals from Dzhezkazgan, Kazakhstan). Less commonly it is found in cubes showing slight modifications. Most crystals are slightly to severely rounded, and dull black. Some surfaces are slightly altered, with a steel-blue patina or thin coatings of a green mineral, most likely malachite. A number of specimens seen show bornite coating chalcopyrite, and in some cases replacing it, as in the stalactitic specimens. Some have been labeled as bornite pseudomorphs after chalcopyrite or chalcocite; individual study of these specimens may prove interesting.

The best bornite seen during this study is specimen #569-C 1270 in the Yale collection. It consists of two very sharp dodecahedrons, each measuring slightly more than 3 cm, forming a 5-cm group. with no matrix. Also in the Yale collection are three crystals mounted on wooden pegs, each showing a different form. Some 30 bornite specimens from Bristol are to be found in the Yale collection, ranging from massive to the fine crystals described above.

The Harvard collection has several Bristol bornites, the best being a fine group of sharp dodecahedrons with individual crystals to 2 cm in a 6.25 x 8.75 cm cluster.

Calcite [CaCO.sub.3]

Quartz may be the most abundant gangue mineral here, but calcite is the most important. Its very frequent association with chalcocite, as tiny scalenohedral crystals, is a feature that distinguishes Cornish from Bristol chalcocite.

Calcite occurs in massive form, as druses of tiny crystals, and as larger crystals. The massive material occurs intimately associated with bornite, and formed simultaneously with it, early in the mineral sequence: salt-and-pepper chunks of this type of ore are common. Fine small calcite crystals in druses and as discrete crystals with chalcocite came later in the sequence--Bateman suggests, in fact, that they were the last to form--and it is when these two minerals occur together that they form the finest Bristol specimens. The Pinch/Royal Ontario Museum specimen is one superb example. Another form of calcite, noted here in a specimen from Union College (#286), is a lovely delicate pink color and consists of scalenohedrons in a 3.25-cm subparallel spray freestanding on quartz. Yet another Union College specimen (#319) is similar, but the calcite is white and the quartz has a reddish tinge. The Yale collection has a specimen of the pink calcite (#435), a group of 2-cm crystals. Nailhead calcites occur here as well; the best known is in the Yale collection and is figured in Dana's System of Mineralogy, Fifth Edition, Figure 576. The specimen, acquired from Stadtmuller in 1870, has crystals only 6 mm high standing at the end of a plate of smaller calcites. There are several other examples of this type of calcite in the Yale collection.

Chalcocite [Cu.sub.2]S

Chalcocite specimens from Bristol have been compared favorably with those from Cornwall, England, often considered the premier locality for this copper sulfide. One early writer (Richardson, 1854) was so enthusiastic in his reporting that he compared the Bristol deposit with one of Cornwall's best mines, the Devon Consols. In the 20th century, excellent chalcocite specimens have appeared from several other localities: Michigan, Tsumeb, Kazakhstan, Australia, and most especially the Flambeau mine, Ladysmith, Wisconsin. But Bristol and Cornwall are the two great "classic" localities from earlier times. Since they were contemporaries, one purpose of this study was to seek out ways one might distinguish examples from these two deposits.

Bristol chalcocite occurs as superb orthorhombic crystals, many showing twinning. Some are heavily striated, others not so prominently so. Crystals often show a pseudohexagonal symmetry, and discoidal pseudohexagonal crystals are common (as also in some of the Cornwall mines). Tabular crystals also occur in abundance. The largest crystal seen in this study is in the Yale University collection: a 6.25-cm deeply striated crystal with several smaller crystals attached. This is a Stadtmtiller specimen (#989-1284). Twinned crystals may be pseudohexagonal, or may be pairs joined on (110) or (032) to form cruciform twins. Most attractive are the "arrowhead" twins wherein tabular crystals join along the (110) faces and are pointed at one end. They are often striated, and often show a small re-entrant angle of matching e faces. One fine example, measuring 2 cm, is in the Harvard collection (#82783).

Significant Bristol chalcocite specimens were seen in several collections. The finest privately owned specimen (at the time seen) was in the William Pinch collection, and is now in the Royal Ontario Museum. All the major Yale specimens, as noted, came in the mid-19th century through Ludwig Stadtmuller, Benjamin Silliman, or (directly or indirectly) Charles M. Wheatley. The collection at Harvard contains several excellent Bristol chalcocites. Of the many specimens preserved at the Smithsonian, two are unusual and noteworthy. Specimen #389-5 is the only example of chalcocite associated with wire silver seen in this study; the silver occurs as fine, hair-like wires with calcite on the chalcocite. The second specimen has a note on its label written by the late collector John Jago, who suggests the presence of freieslebenite, having detected silver and antimony in studies he made of the piece.

Chalcocite was one of the last ore minerals to form at Bristol, along with calcite in tiny white scalenohedral crystals, barite, and quartz. When present, the small white calcite crystals, commonly on a quartz layer but also appearing directly on the chalcocite, seem diagnostic for the locality, as no such association was found on any Cornwall specimens checked. The Cornwall specimens often show a flat "schiefer-type" calcite, distinctly different from the Bristol calcite. Specimen BM1905,207 is one such example on display at the Natural History Museum, London (Embrey and Symes, 1987).

Frequently observed in this study, and also mentioned by Embrey and Symes 1987), is a black, sometimes bronzy, very soft soot-like coating on crystals of chalcocite. Its exact identity is currently unknown, but it may be djurleite. Some collectors say that this sooty coating can be easily removed by a quick wash in a weak phosphoric acid solution, followed by a thorough rinse and neutralization. (As we cannot personally vouch for this method, it would be wise to experiment first on a low-value fragment before attempting to clean a high-value specimen.)

Chalcopyrite Cu[FeS.sub.2]

Chalcopyrite is ubiquitous in the Bristol vein system. It occurs as small grains in the rock, and as discrete crystals showing the normal tetrahedron form, usually on white quartz on schist. It is often iridescent. In one specimen at Wesleyan University, Middletown, CT (#2646), 1.25-cm chalcopyrite crystals are associated with massive pyrrhotite. One Union College specimen (#121) shows chalcopyrite associated with white barite replaced by quartz; another Union College specimen (#60) has several fine rosettes of small crystals, the rosettes ranging up to 2.5 cm across, coated with a thin dusting of bornite. This combination was seen time and again during this study.

Chalcopyrite also occurs commonly in mammillary form at Bristol, with knobs to 2.5 cm or more, jutting from thick massive crusts of the mineral. The chalcopyrite has a hackly surface and a dull luster, and is often coated with iridescent bornite. The most unusual form of chalcopyrite observed in this study does not seem to have been reported in the literature on the deposit. Specimens at Yale, Union College, Wesleyan and Harvard all show stalactitic or tube-like, curving forms, sometimes associated with club-like growths. Some of the tubes are hollow, or have black (bornite?) cores; they are often coated with bornite, and may be iridescent. They range from toothpick-sized to pencil-sized. No other mineral save bornite seems to be associated with this form of chalcopyrite at Bristol.

Bristol chalcopyrite is associated with a greater variety of minerals than any other species in the deposit. It can occur with quartz, calcite, bornite, barite, dolomite, siderite, galena, sphalerite, and rarely with chalcocite. Bateman (1923) also reports chalcopyrite associated with covellite, but only in his thin section studies.

Copper Cu

There are some reports of copper occurring in the Bristol ores but none was seen during this study. Specimens of native copper, and native gold as well, reportedly found during the promotional days of the very late 1800's, were likely the result of salting by the promoters. One newspaper account of 1889 mentions a Mr. Elijah Roberts, formerly of the Lake Superior copper region, as working at the mine. Accounts by Harte (1944) and Peck (1932) refer to native copper, and more particularly native gold (see also Perry, 1975) appearing during the 1890's promotional period.

Another name that surfaces has already been mentioned: Mr. Allen, the former Western miner. Peck reports that the mysterious boxes shipped to Allen from the West during his tenure as mine captain were of great weight. One only has to read the skeptical accounts in newspaper articles of the time to realize that reports of quantities of native copper and native gold being found during this time period were at the least overenthusiastic and at worst downright hogwash. However, Moore (1999) mentions seeing some native copper specimens from Bristol in the Yale collection.

Covellite CuS

Bateman (1923) mentions covellite as seen only in thin section studies. He suggests that the lack of covellite is a significant indicator in the paragenesis of the deposit.

Cuprite [Cu.sub.2]O

Schairer (1931) mentions cuprite from Bristol, without details. None was seen in this study.

Digenite [Cu.sub.9][S.sub.5]

Specimen #1839 at Wesleyan is labeled "chalcopyrite and digenite." The label is dated 1883 and has no documentation to support the species attribution. No other specimens of this mineral were seen during this study, although it is speculated that some of the sooty coating may prove to be either digenite or djurleite.

Dolomite CaMg[([CO.sub.3]).sub.2]

The Yale collection contains at least one example of dolomite from Bristol. Specimen #442 shows 2-cm curving crystals of white to tan color associated with chalcopyrite. Another specimen (#426) is labeled quartz but is clearly dolomite, with crystals to 3 mm on a 5 x 7-cm matrix.

Galena PbS

Hurlbert (1897) reports that galena at Bristol is silver-bearing. He describes "a stratum of galenite carrying a wonderfully rich percentage of silver [with] zincblende and striking ores of copper." Only one galena specimen was examined during this study--Yale #60-C1644-734. It consists of simple 2.5-cm cubes with minor octahedral modification. Small quartz crystals are implanted on some of the galena faces, and chalcopyrite is associated.

Malachite [Cu.sub.2]([CO.sub.3])[(OH).sub.2]

Malachite occurs as green coatings on bornite. Thin stringers of a green mineral seen in massive bornite are probably also malachite. The best Bristol malachite specimens are in the Wesleyan University collection in Middletown, Connecticut. Specimen #8719 is a l0 x 12.5-cm plate of rock with the upper surface covered with pale green botryoidal malachite bubbles measuring up to 1 cm across. Specimen #4568, the best seen in the course of this study, is a 2.5 x 3.5-cm fibrous mass of the green mineral.

Pyrite FeS2

Bateman reports massive pyrite, and one specimen of a distorted pyritohedron, but a search of the Yale collection did not reveal the piece.

Quartz Si[O.sub.2]

Quartz is the most common gangue mineral in the deposit: foot-wide massive veins have been reported in the vein system. Bateman (1923) reports that this is low-temperature quartz. The mineral is most often seen as comb-like layers of crystalline material formed directly on the rock, a palette upon which Nature has arranged finely crystallized ore minerals. Some of the nicest specimens from Bristol are crystals of chalcocite on comb quartz, or intergrown with quartz. Discrete quartz crystals were also found, as small prisms terminating in rhombohedral faces. Union College specimens #53 and #54 both show layers of quartz points to 1 cm, mottled gray-white and completely covering the rock matrix; perched on the quartz are barite blades of exceptional form. A third Union College specimen (#121) is a boxwork of white quartz which may well be a pseudomorph after barite, with minor chalcopyrite. The entire specimen is a 10 x 15 cm mass, with blades to 3 cm across. Harvard specimen #117773 is similar, with blades to 1 cm, and minor calcite and chalcopyrite.

Silver Ag

Silver was one of the minor but important ore minerals at Bristol. Its presence is reported often in the old literature, but only one specimen was seen during this study (as already mentioned). Smithsonian specimen #C389-5 consists of small chalcocite crystals intergrown with white scalenohedral calcite crystals to 4 mm long; the silver is seen as hair-like wires to perhaps 5 mm projecting from the chalcocite, and also as suspended networks of hairs across the calcite. Early assays of Bristol ore done by LeDoux and Company, New York, and reported in the Bristol Herald (November 21, 1889) describe silver ore assaying 17-23 ounces per ton. Remember, however, that this too was during the promotional days.

Sphalerite ZnS

Seen only sparingly in this study, sphalerite occurs at Bristol with chalcopyrite or quartz. Yale specimen #906-C2220 is a fine interpenetrating twin of very pale yellow color, showing a typical resinous luster, with chalcopyrite, Crystals of this type, famously found at Franklin, New Jersey, were once referred to as "cleiophane" and have a very low iron content. There is a similar Yale specimen (#907-C2221) of pale yellow resinous crystals to 5 mm, with bornite on quartz.

Other Minerals

Some gangue and accessory minerals, including muscovite, biotite, garnet and tourmaline, were seen only as grains in rock, or else were mentioned in the literature or collection catalogs but were not available for study. Still others, such as talc, garnet and magnetite specimens seen at Yale, were simply labeled Bristol and could well have come from other occurrences.


The writer is indebted to Wendell Wilson for suggesting this project, and to Dr. Carl Francis of Harvard for his expert help and early review of the manuscript, and to Dr. Wilson and Thomas Moore for editing and augmenting the text. Collection curators who were generous with their time while allowing me free access to the collections in their charge include Herman Zimmerman, Union College; James Gutman, Wesleyan University; Ellen Faller, Yale; and Paul Powhat, Smithsonian. Historian Barbara Narendra of Yale was most helpful in obtaining references, as was the staff of the Bristol Public Library. Dr. William Furness of Bristol gave generous advice. The Wotton Construction Company of Bristol kindly allowed me access to the old mine properties. Juliet Reed of Bryn Mawr gave helpful information, as did Mr. Larry Conklin. Jay Lininger, editor of Matrix, provided some historical illustrations. My good friend Russell Jones was kind enough to provide encouragement while assisting me in some of my research and travels during this study.


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Date:Nov 1, 2001
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