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The Konigskrone lopaz mine Schneckenstein, Saxony, Germany.

For over 250 years, the world-famous Schneckenstein occurrence in Saxony yielded extraordinary crystals of wine-yellow topaz. It may be considered the type locality for topaz, and was for many years the primary source of gem topaz in Europe. Schneckenstein crystals were measured and illustrated by Hauy for his ground-breaking work on crystallography published in 1801, and have been illustrated in many other works since that time.

The site has a long and involved history of mining and collecting and, amazingly, is not yet exhausted.

INTRODUCTION

The mineral-rich Erzgebirge ("Ore Mountains") straddle the boundary between Germany and the Czech Republic. In the western part of the range, just north of the border, lies the famous Schneckenstein locality, known for centuries as a source of yellow gem topaz. In fact, the Schneckenstein occurrence appears to have been the primary source of yellow topaz gems in Europe until the "Imperial" topaz from Ouro Preto, Brazil began replacing it in the 1770s (see Cassedanne, 1989).

Topaz is found throughout the region, in pegmatites and in greisens in and adjacent to cupolas of a large batholith that underlies the area. This tin-topaz province is 150 km long and 60 km wide in places. Granite crops out in 20% of the area, and lies at a shallow depth under much of the other 80%. The cupolas which developed in the apices of granite plutons contained a high concentration of volatiles (which deposited the rich metalliferous veins of the region) as well as the fluorine necessary to produce topaz. More than a thousand mineralized areas are known in this district (Laznicka, 1985), yielding ores of tin, tungsten, silver, copper, iron, lead, zinc and uranium, as well as fluorite, barite and topaz at many of the localities. Pale yellow topaz is found at Sadisdorf and Niederpobel, whereas Schneckenstein is noted for topaz of a pleasing wine-yellow color.

LOCATION

The Schneckenstein (literally "snail-stone"), a small rocky prominence or monadnock standing about 24 meters high, is located about 10 km south-southeast of Falkenstein and 30 km northeast of Bad Elster in the Vogtland region of Upper Saxony, Germany. (Leithner, 1980). It is the remnant of a volcanic plug which tapped the magma body that, upon cooling, formed the Eibenstock granite that underlies much of the area. The source of the name is unknown; perhaps the early inhabitants thought the rock looked like a snail shell. Or per- haps it drew its name from the nearby village of Schoneck and was originally called the "Schoneckenstein"; the citizens there referred to their town informally as "Schnock," which could easily have been transformed over time into "Schneck" (Russ, 1989).

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HISTORY

In 1723, the gemstone inspector in Schneeberg, Christian Richter, told Ignaz von Born, an Austrian mining geologist, the following story about the initial discovery of topaz at Schneckenstein. A tailor living in the village of Stutzengrun had told Richter what he had heard from a man who was a charcoal maker in the forest of the Schneckenstein area. While collecting wood for his business, the charcoal maker discovered a rock with "Zacken daran hingen die weiss, gelb, und grun aussagen ("jagged pieces attached to the rock, having white, yellow and green colors"). Richter went to the location to see the rock for himself; unfortunately he failed to recognize that the "jagged pieces" were, in fact, topaz crystals.

Apparently the charcoal maker also told others about the find. In 1727, Christian Kraut, a fuller and draper from the town of Auerbach, developed the Schneckenstein location into a mine "fur Christallen-Stein und allerlei Metall und Mineralien" ("For crystal specimens, all sorts of metals and minerals"). From that point onward the quiet times in the area were over. Kraut began mining on April 8, 1727, with the permission of von Trutzschler, the property owner, but on July 2 his operations were suspended by order of the mining office. Elector August II The Strong (1670-1733) of Saxony, having become interested, purchased the property from von Trutzschler and then, two months later, authorized Kraut to continue mining and selling the topaz; he called the Schneckenstein workings the Konigskrone ("Kings Crown") mine. Of course, the Elector required that the best topaz crystals had to be turned over to him; crystals of lesser quality were sold to pharmacists, along with the associated quartz crystals, for 16 groschen (about 80 cents) per pound. The pharmacists, in turn, sold the crystals to buyers in Bohemia and in Venice, Italy and elsewhere for cutting. The cut gemstones then came back to Saxony as "oriental topaz," with improved value and higher prices.

In the fall of 1727, Kraut founded a labor union with people mostly from the Elector's court in Dresden. Present from the beginning was the famous art lover Count Heinrich von Bruhl, who later became quite powerful as prime minister of Saxony. At about the same time that mining started at the Konigskrone mine, the area was surveyed, staked out and handed over to the topaz union. Steady mining from then on was carried out using hammers and chisels, drilling and blasting, followed by hand-sorting to recover the topaz. To make the topaz more easily visible, the rock was washed with water from a well: in the realistic engraving by Charpentier (1778), the windlass for this well is clearly visible near the miners' barracks.

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In 1728, just one year after topaz mining began at Schneckenstein under the direction of Christian Kraut, Dr. Johann Adam Goritz of Regensburg, Bavaria published a report on the topaz discoveries at Schneckenstein. Johann Friedrich Henckel (1678-1744), a member of the Freiberg Mining Board, was a physician and mining inspector, and in the latter capacity he visited the topaz quarry several times between 1737 and 1739. In his 1737 reports on the mine Henckel is believed to be the first person to apply the name "topaz" to what we consider as that mineral today; up to that time "topazius" had been the name for peridot olivine.

After 1739 the labor union was unable to work the site profitably. Highgraders were a serious problem; they appeared at night and on Sundays, and the illicit collecting could not be stopped because the location was too remote.

The vice-inspector of mines in Freiberg, Johann Gottlieb Kern, visited the Schneckenstein, where he made notes and drew sketches of the outcrop, and then wrote a "Mining Report" in 1740. He expressed his concern that blasting might destroy the Schneckenstein rock. In 1744 Kern wrote (but did not publish) his Umstandliche Beschreibung des Schneckenstein, oder des sachsischen Topasfelsens ("Detailed description of the Schneckenstein, or the topaz rock from Saxony"). This work appears to be the first publication ever devoted to a specific gemstone deposit. Kern was interested mainly in studying the topaz occurrence for clues that might lead to the discovery of other gemstone deposits. However, he never published his two papers. In 1776, following Kern's death, Ignaz Edler von Born, the prominent Austrian mining geologist, organized and edited Kern's work for publication.

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According to Lahl (1990), only four or five topaz crystals out of a hundred were of high enough quality to be faceted. Gemmy quartz crystals between 1 and 3 cm in size were also cut. It was reported that the production of gem topaz during the year 1738 totaled about 32 kg. The best topaz gemstones were graded into three categories called "ring stones," "shirt-button stones," and "clasp stones." The very finest of the faceted topaz gems were the most sought after, and were set in rings. Material which could only be used to frame larger gemstones in a piece of jewelry was called carmosier. The lowest quality was called brack, the designation for "unreines Gut--so nicht zu gebrauchen" ("dirty stones--not usable"). The biggest ring stone, according to the ledger at the Konigskrone mine, weighed in at 8.5 carats.

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One story from the early days of mining relates that a member of the mining crew had stored quite a lot of topaz crystals in his home; after a fire destroyed the house, other miners searching through the rubble found about 50 kg of topaz which had been turned from yellow to colorless by the intense heat.

The union ended mining at Schneckenstein in 1744. But from 1751 to 1757, under the management of Edlen von der Planitz, mining resumed. Between 1759 and 1796 the Schneckenstein was worked on a limited scale by the Vice-Mining Director of Saxony, Peter Nikolaus Freiherr von Gartenberg, but in 1788-1796 mining was greatly reduced because of poor sales. The locality was patrolled to keep the robbers away, and specimen material, including turbid (non-gem-grade) topaz crystals, was collected on a small scale. The old dumps were also worked over for specimens. From its establishment in 1727 until 1797 the total output of the mine has been estimated at about 150 kg of topaz crystals.

On August 8, 1800, the Elector granted permission to the Mining Academy in Freiberg to work the Schneckenstein dumps for topaz specimens and to occasionally do some blasting in the rock as necessary; this permission lasted until 1847. Between 1849 and 1851 C.A. Loffler, a miner from Freiberg, became successor in the mining school's mineral sales department with the stipulation that he mine only on the south side of the Schneckenstein; this was the first attempt to preserve the rest of the occurrence for later generations. The mining carried out by Loffler was the last to occur at Schneckenstein.

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But even after formal mining had ceased, collecting at Schneckenstein continued. Frenzel, writing in 1874, stated that there had been a bustling trade in Schneckenstein topaz specimens in the past, but that at the time almost nothing was being found. Nevertheless, collectors and gem hunters have been finding crystals sporadically at Schneckenstein even in recent decades.

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GEOLOGY

According to Mende (1929), the topaz at Schneckenstein was created by contact of the Eibenstock-Neudecker granite massif with older schists, which had been under tectonic pressure from the northeast, compressing and laminating the schist formations. At weak spots and northwest-facing pressure-fissures, granite magma welled up (Fig. 8) and in the process altered the surrounding country rock through contact metamorphism. This created an an andalusite-mica-cordierite hornfels skarn, as well as mottled schist and fruchtschiefer (a kind of spotted slate). The contact aureole is about 2 km wide.

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At the same, time, deformation of the overlying rocks, as well as vertical movements at the contact between the granite and the newly formed schist, created brecciated zones. The volatile components (F, CI, B, and [H.sub.2]O) of the residual solution reacted with the new contact-metamorphic minerals, forming tourmaline schist from andalusite, and topaz and quartz from feldspar, generating the tourmaline-topaz-quartz breccias. Around the same time, the granite margin was impregnated with cassiterite, leading ultimately to the formation of greisens.

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The geology of the topaz-bearing body at Schneckenstein has been well defined by drilling and underground workings which extend to a depth of 50 meters. Figure 8 shows an east-west cross- section through the Schneckenstein volcanic vent and through a related vent nearby. The country rock is a hornfels which was brecciated and altered in the Schneckenstein vent pipe. The material within the vent consists of fist-sized fragments of country rock altered to a quartz-tourmaline-topaz rock, cemented together by a white to yellow quartz and wine-yellow topaz.

Numerous late-stage veins (not shown in Fig. 8) containing Fe, Cu, Pb and Zn sulfides cut the vent rocks, the hornfels, and the underlying Eibenstock granite. Late-stage solutions have altered the topaz in places to kaolinite. The Schneckenstein occurrence is genetically similar to the tin deposit at Mount Bischoff, Tasmania.

The rock in the second vent is a quartz porphyry which also contains topaz, and there is a long contact zone into which a lamprophyre was intruded.

Minor minerals contained in the cement of the breccia body at Schneckenstein include tourmaline, fluorite, wolframite, molybdenite, ilmenorutile, apatite, chalcopyrite, malachite, azurite, and (rarely) cassiterite, turquoise, pyrite, wavellite and gold. The breccia is characterized by numerous vugs reaching 30 cm across, containing transparent quartz and gemmy topaz crystals. Minor tourmaline, fluorite, and pyrite are also found within the pockets.

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In 1950 a tunnel was driven from the 775-meter level of the Tannenberg tungsten-tin mine near the town of Muhlleiten to the Schneckenstein volcanic pipe. Where the tunnel intersected the pipe at a depth of about 100 meters below the surface, the pipe was found to measure about 35 X 110 meters, with very sharply defined contacts with the surrounding phyllite. The topaz-rich breccia showed essentially the same mineral assemblage as that found at the surface outcrop, but with some differences in relative proportions with depth. Tourmaline and wolframite were more common at depth than near the surface, whereas topaz was seen to be less common, and molybdenite was found only in the lower zone (Russ, 1989).

Paragenesis

A greisen is defined as a pneumatolytically altered granitic rock composed largely of quartz, mica and topaz. In the greisenization process, often taking place in the fractured rock above a magma chamber, feldspar and muscovite are converted to an aggregate of quartz, topaz, tourmaline and lepidolite by the action of water vapor containing fluorine (Jackson, 1997). Topaz-formation temperatures in greisens are at or below the solidus temperature of the magma; topaz crystals formed in this setting are generally small. Sehnckenstein is an example of a topaz greisen that has been a historically important gem topaz producer.

The relationship of the temperature of formation of topaz to its F/OH ratio is worth considering. Empirical evidence suggests that formation temperature is an important (but probably not the only) factor in determining the F/OH ratio. If this is the case, then variations in physical properties can provide useful clues to the origin of individual crystals. Rosenberg (1972), in his studies of synthetic topaz, showed a direct relationship between the formation temperature and the F/OH ratio. Lower temperatures were associated with a higher OH content. These data, he pointed out, were valid only for formation under closed-system conditions. Many geologists believe that most pegmatites form as closed systems, so that Rosenberg's data may be used to estimate formation temperatures of many pegmatitic topaz occurrences.

Roedder (1984), on the other hand, believes that pegmatites generally form as open systems, and that the gemmy, euhedral crystals present in the pocket pegmatites formed by crystallization from a hydrothermal fluid, not a melt. The fluid-inclusion studies of Roedder provide some additional information to help in defining the formation temperatures of some topaz. Unzoned pegmatites have inclusion-homogenization temperatures of 690 to 540[degrees] C, and thus the pocket pegmatites would probably form below this range. Inclusions in topaz from the Volynsk region in the Ukraine have been studied extensively by Russian researchers. Roedder, in discussing those studies, notes that homogenization temperatures as high as 740[degrees] C have been erroneously reported for this material, and that values closer to 400[degrees] C, obtained on selected inclusions, more probably represent the approximate formation temperature. He also discusses the homogenization temperatures of minerals obtained from a number of tin-tungsten greisens, showing a range of from 150 to 600[degrees] C. Most temperatures are in the range of 300 to 400[degrees] C. In most of these deposits topaz is believed to predate the ore minerals, so that it would be expected to have somewhat higher homogenization temperatures.

[FIGURE 12 OMITTED]

A homogenization temperature for topaz from Schneckenstein has been reported at 554[degree]C (Roedder, 1984).

SCHNECKENSTEIN TOPAZ

Early Illustrations

The earliest illustration of a Schneckenstein topaz specimen appears to be that of Fabien Gautier d' Agoty, in his Histoire Naturelle Regne Mineral (1781). His plate no 54 shows a hand-colored illustration of a superb cabinet specimen, 14 cm across, with a pocket filled with quartz crystals and yellow topaz crystals to 2.5 cm. The illustration was drawn by Francois Louis Swebach Desfontaines (ca. 1740-1792) from a specimen in the collection of Jean Gigot d'Orcy (1733-1793) (Wilson, 1995). Gigot d'Orcy lost his life in the French Revolution, and his mineral collection was later sold to a wealthy American collector, Col. George Gibbs (1776-1833); Gibbs sold his 20,000-specimen collection to Yale University in 1825 (Wilson, 1994). The Schneckenstein specimen (or at least a ghost of it) survives there today, but most of the fine topaz crystals have been broken off, with only the broken crystal bases remaining on the matrix (see the photo in Moore, 1999).

Feuchtwanger (1859) describes crimson as well as yellow Saxon topaz, and Streeter (1877) mentions that white, yellow, and pale violet crystals were found. The lamprophyre present in the deposit may have been the source of the chromium which presumably lends the crimson or violet color to the crystals.

Brauns (1903) published a chromolithographic illustration of a matrix specimen of Schneckenstein topaz, and two single crystals. Bauer (1904) shows a color comparison between typical pale yellow Schneckenstein topaz and more deeply colored Ouro Preto topaz, as well as illustrating the typical habits of crystals from both localities. The Schneckenstein crystals generally have a large well-developed basal pinacoid that is not seen on Ouro Preto crystals. Also, Schneckenstein crystals are generally smaller, averaging only about 1 cm--the largest may reach 5 cm across and 9 cm long, but such large crystals are quite rare. Another source (Lahl, 1990) mentions a topaz crystal weighing 220 carats; the largest faceted Schneckenstein topaz known is a 176-carat stone in the Green Vaults of Dresden.

Chemistry

Topaz is an aluminum fluorosilicate having the formula [Al.sub.2][SiO.sub.4][(F,OH).sub.2] The composition is relatively invariant except for the substitution of OH for F. This substitution is limited to a maximum of about 30 mole % OH in place of F in natural topaz. Pure hydroxyl-free topaz contains 20.6 weight % F. Near end-member topaz was reported from Schneckenstein by Fricke (1949), containing 18.62 weight % F, 56.54 weight % [Al.sub.2][O.sub.3] and 33.53 weight % [SiO.sub.2].

The F/OH ratio in topaz affects many physical and optical properties, which vary continuously as a function of the ratio. Consequently the properties of the mineral vary along a continuum, i.e. the gemological literature is misleading when it describes, as it often does, merely two distinct types--a low-density type with high index of refraction and yellow to orange color, and a high-density type with low index of refraction and a blue to colorless appearance.

Crystal Morphology

Hauy (1801) was the first to describe and illustrate the richness of crystal forms and habits shown by topaz from Schneckenstein (Fig. 13). More than 140 different forms were reported by Frenzel (1874). The morphological features of topaz observed in many crystals belong to the orthorhombic dipyramidal class 2/m 2/m 2/m, and space group Pbnm (Gaines et al., 1997). Parise et al. (1980) and Frye (1981), however, state that topaz can also be triclinic pseudo-orthorhombic (space group P1). The higher hydroxyl content is the culprit, and a pyroelectric property also appears. As stated earlier, the habit of a topaz crystal is a complex function of the physicochemical conditions under which it grew.

[FIGURE 13 OMITTED]

Several different environments or models have been observed for the primary formation of topaz. These are, in order of decreasing temperature of formation: topaz rhyolites, pegmatites, greisens, and hydrothermal veins. Pough (1964) has described the typical habits associated with each of these genetic models, lumping the pegmatitic and greisen modes of formation together because crystals from them show no difference in habit. His summary of the typical habit is as follows: For rhyolitic topaz, a fairly large basal pedion {001} with two equally developed prisms (third order, {110} and {120}, two dipyramids typically {h11} and {112},two first-order prisms typically {021} and {hkl} and one second-order prism). For pegmatite/greisen topaz, a large basal pedion {001}, with one or two domes and one or two dipyramids is more typical. (He does not mention the third-order prisms.) The habit of the vein-type topaz as at Ouro Preto, Brazil, is characterized as being long and slender, terminated by a simple dipyramid {123}, and not at all like pegmatitic topaz.

The prism faces of topaz crystals commonly show longitudinal fluid cavities and incipient transverse cleavage which can produce iridescent colors. They are usually attached to matrix at one end and thus usually show a cleavage plane so that doubly terminated crystals are rare. Hemimorphic topaz crystals (though common in the Ouro Preto deposits) and twins are unknown from Schneckenstein.

Color

Agricola (1546) wrote: "Auri autem fulgor topazion a callaide pallidius virente separate" (the head-color of the topaz is wine-yellow), but he was probably referring to olivine. It appears that Henckel (1737), in describing the yellow topaz from Schneckenstein (topazius vera Saxonia), was the first to assign the name "topaz" to the aluminum fluorosilicate that we know today by that name. A yellow color in topaz has been reported with increased amounts of chromium, manganese, cobalt and vanadium (Deer et al, 1982). Traces of chromium (less than 100 ppm) have been reported in high-fluorine topaz from Schneckenstein (Ribbe and Rosenberg, 1971). The yellow color of Schneckenstein topaz, however, is thought to be due to the presence of color centers--defects in the crystal structure that selectively absorb a component of visible light (Petrov, 1978). The topaz at Schneckenstein varies from colorless to wine-yellow, honey-yellow, dark-yellow, orange, rose-red, wine-red, pale violet and green ("Saxon chrysolite").

THE SCHNECKENSTEIN NATURE MONUMENT

The Schneckenstein is one of Europe's most famous nature monuments. In early reports the bridge to the fault pit and the nearly buried shaft head were mentioned as historically important mining artifacts. In 1902 the Naturfreunde ("Friends of Nature") of Klingenthal constructed a railing to make the climb up the rock easier; it was replaced in 1960. There are also hand-hewn stone steps that probably date back to 1829.

[FIGURE 14 OMITTED]

[FIGURE 15 OMITTED]

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In 1937 the area encompassing the Schneckenstein rock and all the dumps came under governmental protection and was declared a Nature Monument. However, conservation efforts around the Schneckenstein were not very effective prior to 1973; unauthorized mineral collecting there continued apace and the dumps were getting larger every year. Spruce trees growing at the edge of the forest were undermined by diggers and eventually fell down. The foot traffic of an increasingly large number of visitors prevented young trees from taking hold up to 30 meters from the rock. Then in 1973 the protected area around the Schneckenstein rock was enlarged, a fence was erected, and visitors were thereafter required to stay on clearly marked paths; specimen collecting was prohibited.

For many years, and especially since the beginning of the 20th century, the Schneckenstein has been a magnet as a scientific destination for mineralogists, geologists and amateur collectors. Hikers can reach the locality from the town of Muhlleiten-Tannenbergsthal. Another trail goes from the Muldenberg dam to the monument in about an hour and a half on foot. The mixed woods prevent a clear sight toward the Schneckenstein, especially coming from the southwest, but when visitors finally reach the top of the rock at about 860 meters elevation they are rewarded with a fine scenic view that they will remember for a long time.

A large number of topaz specimens have been collected at the Schneckenstein over the years, and consequently even today a collector can still purchase Schneckenstein topaz on the mineral market.

ACKNOWLEDGMENTS

The author gratefully acknowledges the generous assistance of Dr. G. Sansoni and A. Massanek in Freiberg; K. Fischer in Starnberg; G. Hofmann in Nurnberg; P. Huber in Wiener Neustadt; S. Schiller in Falkenstein; and K.H. Russ in the U.S.; Dr. A. Kampf in Los Angeles and Dr. W.E. Wilson and T.P. Moore in Tucson reviewed and augmented the manuscript. My thanks go as well to the many photographers who submitted photographs.

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Helmut Leithner

Kreisstrasse 12

D-90596 Schwanstetten

Germany
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Date:Sep 1, 2008
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