Classic agate deposits: of Northern Mexico.
Since the mid- 1940s, Chihuahua has produced some of the world's finest agate specimens. Although in the past they have not always been readily accepted into mineral collections, today the finer and rarer pieces are vigorously pursued by collectors. Laguna, Coyamito, Agua Nueva, Apache, and Moctezuma are just a few of the classic localities that produce some of the world's most dazzling agates. The names are derived from the ranches on which the agates are found, or the nearest railroad station, or perhaps a nearby village.
The early prospectors and collectors who discovered each of the agate beds were drawn from the ranks of accountants, physicians, legislators, attorneys, machinists, gamblers, and even the penniless; many were highly unusual characters. Several of the pioneers were so convinced of their own superiority that they were destined to collide with each other. In their attempts to outdo each other as collectors or owners of the finest agate specimens, they promoted discovery and exploitation of some of the richest agate beds in the world. Without their jealousy and hatred of one another to motivate them, they would not have accomplished as much as they did.
Mexican agates show most of the features known in agates of volcanic origin worldwide. Moss, plume, sagenite and banded (fortification) agates are found throughout the country. This article concentrates on several of the more popular types of rare banded varieties of agate from Northern Mexico, and provides precise geographic coordinates for several of the more important localities.
Museum-quality agates have never been plentiful, even in the 1940s, when large-scale surface collecting began. High-quality banded agates with bright, contrasting colors, complete patterns, no fractures or cracks, and no crystalline quartz centers have always constituted only a very small percentage of the whole (on the order of 3% or less). The highest-quality specimens command prices comparable to those of the finest crystal specimens from Mexico.
Agate bands form in scalloped and undulating layers that more or less follow the shape of the original vesicle or vein. It is not at all unusual for the bands to make sharp, angular turns that resemble the parapets of old fortresses: thus the term "fortification" agate. The bright, vivid colors found in Mexican agates surpass the range of colors common for most individual mineral species, and the pseudomorphs of agate after aragonite are among the best found anywhere.
There are currently over 100 different varieties of agate from Mexico; a number of observable features which are characteristic of the various types of banded agates are key in distinguishing one variety from another. These characteristics include color dominance, nodule size, exterior rind, distinctiveness of banding, inclusions, presence of pseudomorphs, and weathering.
Much of the Mexican agate story begins with the Rancho El Agate andesite flows some 38 million years ago (Keller, 1977). These ancient flows contained gas vesicles that later became filled with silica and various coloring agents (primarily iron and manganese oxides) to produce some of the most exquisite specimens in the world. Weathering and erosion broke down a portion of the flows, and the more resistant agates were freed from their host and scattered across the desert floor. Most of the early agates were found as residual surface nodules, although some limited hand digging was done. In the early 1960s, pits and trenches were dug into the tenacious andesite, with no guarantee of success to their diggers. It wasn't until the early 1990s that mechanized mining with heavy machinery began, but even today such mining is sporadic. Although some of the older deposits are probably now depicted and offer little to no mining potential, others still hold the promise of yielding good agates.
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The agate-producing region in Mexico begins north of Villa Ahu-mada, Chihuahua and extends in a southerly direction for the next 80 miles to Estacion Ojo Laguna. The belt then trends to the west-northwest to Casas Grandes (where the Casas Grandes, Parcelas. and Apache varieties occur) and on up into southern New Mexico. The loop is then complete if you travel back to the east-southeast and include the popular Mexican Crazy Lace beds found southwest of Villa Ahumada.
SELECTED AGATE VARIETIES
Agua Nueva Agate
Hacienda Agua Nueva on Rancho Los Nogales. Chihuahua, lies about 135 miles south of El Paso, Texas, in the southeast quadrant of the Sierra del Gallego (host to the Sueco, Gallego, Derramadero, Agua Nueva, Aparejos, and Coyamito varieties). The northernmost portion of the sierra begins about 120 miles south of El Paso. The agates from this region all originate in what is locally known as the Rancho El Agate andesite, a 38-million-year-old porphyritic andesite. Over the years, this ranch has produced a wide range of agate varieties, including both nodular and vein types. Various isolated areas of the ranch produce specific types of agate with characteristics particular to that area.
Many of the nodules from this ranch contain bands brightly shaded in lavender, purple, gold, pink and yellow. The nodules typically have a gold moss on the outside rim and weigh from a half pound up to 60 pounds. Less than a mile away, the agate occurs as a vein, containing brilliant purple and white bands. Characteristic of this vein are the stunning purple, lavender, and white tubes, some reaching over an inch in diameter. When cut perpendicular to the tube, the concentric bands produce a beautiful "eye," making a splendid addition to any collection.
The first serious mining operations on Rancho Los Nogales were conducted by Francisco Olivas (from Ciudad Juarez, Chihuahua) in the mid-1970s. In recent years, the various deposits on this ranch have been commercially mined by Eugene Mueller of The Gem Shop in Cedarburg, Wisconsin, under the mining concessions Mi Sueno ("My Dream") and Agua Nueva ("New Water").
Apache agate is perhaps one of the most mysterious agates ever found, not only in Mexico but worldwide. Its bright red, vivid orange, and dark yellow colors seem to be suspended in contrasting blue and lavender agate with color patterns resembling splashes, draped folds, and swirling veils. The agate always has a very finely pitted, rough, lime-green exterior that makes it easily distinguishable from other Mexican agates.
The finest museum specimens are obtained from nodules which have cavities showing on their surfaces. It is adjacent to these cavities that the most exquisite patterns and colors tend to occur.
Apache agate is found approximately 5 miles northwest of Ejido El Apache on Rancho La Vinata (about 30 miles southeast of Nuevo Casas Grandes, Chihuahua). The agate deposit was initially discovered in 1957 by Luis Arzola and Jesus Gamon (both from Ciudad Juarez, Chihuahua), and was intermittently worked by hand for a number of years. In 1968, our dear friend Benny Fenn filed claim on the deposit and, with his brother-in-law Harold Jorgenson, extensively worked the area with heavy machinery, producing hundreds of pounds of exquisite agate. Little has been found since then.
This locality produced what may be the world's most famous single agate, known as "the Apache Hooded Owl" (Fig. 44). The agate weighs approximately 1.5 pounds and is an excellent example of a scenic agate.
Aparejos agate is found on Rancho Los Aparejos, located approximately 3 miles north of Rancho EI Agate and on the northeast side of the Sierra del Gallego. The agate was mined in the 1950s from three pits (average 10 feet square and 4 to 6 feet deep) hand-dug into very dense Rancho El Agate andesite.
The distinct banding and the exterior rind make this agate variety almost indistinguishable from the Coyamito agate. Reportedly, much of the fine purple and yellow banded agates once marketed as Coyamito agate actually came from the La Morenita ("The Dark Girl") claim on Rancho Los Aparejos. Other colors found in agates from this ranch include red, yellow, white and blue. Sr. Beto Vasquez (from Ciudad Juarez) was the first to commercially mine Aparejos agate. Beto began collecting nodules and digging pits at Aparejos in 1955, for Manuel Ontiveros (one of our past great mineral dealers).
Casas Grandes Agate
Approximately 10 miles southeast of Nuevo Casas Grandes in the Cerros Las Borrogas area is Rancho Colorado and the La Chocolata claim, regarded as the original locality for Casas Grandes Agate. The banding in this agate is predominantly lavender, gray, white, slate and pink.
The agate was named for its proximity to Nuevo Casas Grandes, a town founded in 1879 as a railroad station on the Ferrocarril Noroeste de Mexico. Up to two-thirds of the nodules from this location are considered "duds." What may appear to be a perfectly solid agate on the outside turns out to be solid psilomelane or other manganese oxides on the inside. The Casas Grandes agate has an extremely smooth skin that is dark brown to reddish brown and occasionally gray. About 50% of the agate nodules contain crystalline quartz centers.
The agate nodules were initially discovered around 1955 and were mined from an altered grayish purple andesite. The most recent mining operation was conducted in the early 1970s by Benny Fenn; it involved the terracing of the mountainside with a small bulldozer. Once a pass was made with the bulldozer, the exposed ground was then searched for agate nodules. Jesus Gamon and Ramon Pena are the men who worked most of this deposit in the late 1950s and early 1960s.
Coyamito agate, commonly containing brilliant shades of red, orange, yellow and purple, is indeed among the very finest agates to come from the Sierra del Gallego area. Agate was first picked up at Rancho Coyamito Norte in the early 1940s by Dave and Lucille Harris of El Paso. In 1948, Ramon Pena filed the first commercial claim at the ranch and worked the deposit for Manuel Ontiveros. Numerous others have since staked their claims in the area; agate has been produced most recently by the ranch owner, Marin Carrillo.
Some very rare color combinations are found in this agate, including purple and yellow, rose and white, various shades of red, purple, and mustard. Many of the Coyamito nodules prove to be hollow, and in many cases a hollow Coyamito will have concentrically ringed cylindrical tubes running through it, producing an attractive "eye" when cut perpendicular to the tube.
There are three primary deposits of agate on the ranch. The Los Alamos ('The Poplars") area is the most southerly and is named for the large trees surrounding a spring which once served thirsty explorers and travelers. The agate here occurs adjacent to the creek bed, and is noted for its dark lavender and yellow bands mat in many cases cover pseudoraorphs of agate after pseudohexagonally twinned aragonite crystals. The agate occurs as nodules ranging from a few inches to more than 12 inches in diameter. The exterior of many of the nodules from this deposit consists of a rust-orange to red, powder-like "limonite."
Just up the hill and only a few hundred yards away is the La Fortuna deposit. Agates from this deposit typically have bright red, pink, orange, yellow, tan and white banding. This nodular agate is completely different in size, external features, and banding color from the Los Alamos agates. The nodules are usually smaller, averaging under 4 inches in diameter; their dark red to brown, siliceous exteriors lack the rough "limonite" coating found on nodules from the Los Alamos deposit; and their external textures are much smoother, with small pin-size pits.
The third deposit at Coyamito Norte consists of an area known as La Sonorena. This deposit is located in the far northern portion of the ranch adjacent to and extending into Rancho Derramadero. While the smooth-skinned nodules here are somewhat small for the deposit (averaging 1 to 4 inches in diameter), these are perhaps the most colorful agates ever found at Coyamito. Brilliant reds, purples, yellows, and oranges are characteristic of this deposit. With many of the La Sonorena agates, one can begin tracing an individual red band around the agate and find that it changes to yellow or orange. Nothing compares to the lovely agates found at this location.
Pseudomorphs of agate after pseudohexagonally twinned aragonite can be found at any of the three deposits. Specimens in which the entire agate itself is a pseudomorph can reach lengths of over 8 inches. It is not unusual to find combinations of purple and yellow bands and a vast array of pseudomorphs within the banded nodule.
Crazy Lace Agate
Crazy Lace or Mexican Lace agate is found in several remote areas of northern Chihuahua; however, the most noted occurrence is northwest of Ejido Benito Juarez in the Sierra Santa Lucia (located approximately 30 miles southwest of Villa Ahumada).
This material has been utilized for years in the commercial cutting of cabochons. The pattern generally consists of many irregular curved and twisted bands. There are zig-zags and scallops, bouquets, sagenites (acicular sprays), sunbursts, and eyes. Many of the internal structures have the appearance of very small, elongated tubes; these are commonly grouped together in larger, radiating spherical aggregates which can reach diameters of up to 4 inches. While most of this vein agate is white to gray, some pieces are naturally stained beautiful shades of red, orange and gold.
Unlike all the other Mexican agates, which are found in igneous environments, this variety is found in a Cretaceous limestone and occurs only in vein form.
Crazy Lace agate comes in several varieties and is usually named after the claim owner or after typical patterns in the agate. The first mining concession on this deposit was filed in 1960 by Beto Vasquez. Additional concessions were immediately filed by Victor Salgado and Juan Noriega (all from Ciudad Juarez). There are currently at least six active concessions in the Sierra Santa Lucia area and up to perhaps 100 separate diggings.
Rancho Gallego has been very prolific in supplying exceptional agate nodules. The nearby railroad station, Estacion Gallego, was the primary shipping point for manganese ore from the Terrenates manganese district in the early 1950s. It was in 1946 on Rancho Gallego that the first banded agates of Northern Mexico were commercially collected.
The primary agate occurrence on the ranch is approximately 5 miles southeast of Sueco and 6 miles east of Highway 45, in the altered Rancho El Agate andesite that forms the rounded eastern slopes of Cerro del Gallego. No pits or trenches have been dug at Rancho Gallego, and little information has been found regarding early mining activities.
Gallego agate characteristically exhibits pink, light red, and gray banding. The bands are not particularly sharp or distinct in most nodules. All agate from the ranch is nodular in form, and it is estimated that 70% of the nodules are hollow. They are generally round and measure only a few inches at most in diameter; their rinds are most commonly chocolate-brown or pale pink.
Gregoria agate occurs in the most southerly portion of the Sierra del Gallego, mid-way between El Sueco and Estacion Ojo Laguna in the Cerro El Ahiujadero ("the calving area") on Rancho La Gregoria. The agate was mined in the late 1950s from several pits hand-dug into the very dense Rancho El Agate andesite.
The agate occurs as banded nodules and exhibits almost every color of the rainbow. Because of its fine and distinct banding, vibrant colors, and smooth exterior rind, it has usually been marketed as Coyamito Agate.
Laguna agates seem to be the most highly prized of all the Mexican agates. This is probably more a function of name recognition than of anything else, as there are other Mexican varieties just as fine in quality. Laguna agates have striking fortifications and a vivid range of colors including red, pink, orange, yellow, purple, lavender, beige, white and gray. The best examples have a combination of colors that provide contrast or a combination of "clash" colors such as purple, red, or orange. Shadow effect, an optical effect created by the perception of depth between the parallel bands of an agate, is not uncommon at this locality and gives the agate a dynamic visual appeal.
One of the most distinguishing features of the Laguna agate is the presence of blue-green celadonite as a coating on the exterior of most of the nodules. The shape of the nodules is roughly spherical or potato-like, with an extremely pitted, pockmarked and highly irregular surface. Laguna nodules range from the size of an egg to the size of a large cantaloupe; the average nodule is between 2 and 5 inches in diameter.
Laguna agate is mined east of Estacion Ojo Laguna, a small railroad station about 145 miles south of El Paso. There are currently 13 separate concessions at this locality including Ojo de San Martin, El Puerto, Laguna, Santa Monica, La Alianza, El Hormiguero, La Morita Uno, Buena Fe, Diana, El Mezquite, El Mezquite J, La Morenita, and Ojo Laguna.
Las Choyas ("Coconut") Geodes
While numerous deposits of geodes and thunder eggs are found throughout the Republic, the largest and most abundant deposit of geodes in Mexico occurs at Las Choyas, about 22 miles east-northeast of Laguna Encinillas and 145 miles south-southeast of El Paso. These quartz geodes, also known as coconut agates, are mined from a 2-square-mile area and have constituted a multi-million dollar business. The deposit was discovered by Ramon Pena in 1961, but it wasn't until 1965 that production finally reached the market. Mineral dealer Jack Young recalls how surprised he and the other El Paso dealers were to see the geodes introduced for the first time at the 1965 Phoenix Gem and Mineral Show. Certainly a discovery of this magnitude couldn't have escaped their notice in El Paso!
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Production records have never been kept; however, it is estimated that over 150,000 pounds of coconuts per year are mined from these claims. Although this production may seem quite high, only 20% of the nodules mined prove to have the desirable hollow centers.
The geodes occur as spherical cavity fillings in an intensely altered, feldspar-rich ash flow tuff. The producing unit is locally known as the Liebres Formation and is about 44 million years old, making it one of the oldest volcanic units in the agate-producing region.
Because of the westerly dip of the geode-containing formation, current mine shafts reach depths of up to 200 feet. All mining activity is conducted on ranchland owned by Hector and Jeannette Carrillo of Gem Center, USA in El Paso, Texas.
The geodes commonly have a blue-gray chalcedony or siderite lining that grades inward into well-defined crystalline quartz with discrete crystals whose apices point toward the center of the geode. Varieties of quartz found within the geodes range from clear to smoky to amethystine, and over 18 different microscopic minerals have been identified within the geodes (Keller 1977). Other secondary mineralization includes several varieties of calcite as well as a number of zeolite minerals.
Loma Pinta Agate
Loma Pinta ("Painted Hill") nodules are found on the southeastern flank of Cerro Brajo de Diablo ("Devil's Needle Mountain"), some 15 miles east of Estacion Moctezuma. The name "Loma Pinta" was given to the agate by Dr. I. M. Epstein, an El Paso pediatrician and agate collector, in the 1950s and 1960s.
Loma Pinta agates typically exhibit grayish shades and tints of pink, pale orange, pale yellow and red. The banding tends to be comparatively shallow and irregular. The nodules are generally spherical, and the outer coating or rind is typically very smooth and is reddish brown to green.
The agate was initially mined by Tomas Saenz (of Ciudad Juarez) and Jesus Gamon. The deposit has not been actively worked since the early 1970s.
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Moctezuma agate is a nodular banded agate with bands in pastel shades of pink, yellow, salmon and tan, as well as white. The banding varies from fine to somewhat heavier. The agate is easily distinguished by its siliceous white "banana peel" exterior, caused by extensive weathering. The vast majority of these nodules range from 1 to 3 inches in size.
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"Chromatography," a color-change feature commonly seen in Moctezuma agates, is caused by the separation of coloring agents by semi-permeable layers of chalcedony.
Moctezuma agate is found approximately 15 miles east of Estacion Moctezuma, Chihuahua, as float material in the desert flats of Ranchos San Martin and Barreal. At the Laguna Verde ("Green Lagoon") claim, Moctezuma nodules can reach more than 12 inches in diameter. However, most of these large nodules are composed entirely of crystalline quartz with only a thin outer rim of vivid salmon-pink and yellow bands.
Parcelas agate is found in the Cerro El Oregano area, 8 miles northeast of Le Baron, Chihuahua. Parcelas agate has many times been mistaken for and marketed as Casas Grandes agate; however, the respective nodules are easily distinguishable both externally and internally. Parcelas agate rinds are fairly rough in texture and are gray, red and green. Their interiors show lavender as well as pale to dark gray banding. The vast majority of the nodules have alternating pale and dark gray bands. The individual bands are usually quite wide compared to other Mexican banded agates. Many nodules were once hollow and have since been filled with manganese minerals (primarily psilomelane and cryptomelane), the probable coloring agents for the agate.
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Parcelas agate was initially discovered by Francisco Lucero (from Carmen, Chihuahua) in the late 1950s. The deposit was later mined by Benny Fenn under the concession Las Parcelas ("The Parcels").
Rancho El Sueco, located in the northwest quadrant of the Sierra del Gallego, produces agate nodules in a wide range of colors, although red, purple, olive, and yellow shades predominate. Identified by their rusty yellow and pitted exteriors, the nodules typically range from 1 inch in diameter up to 5 or 6 inches. It is estimated that more than 80% of all the agates recovered from Sueco are hollow.
Jesus Gamon is credited with the early mining of the majority of the Sueco agates. In recent years, the deposit has been mined by Ramon Olivas (from Ciudad Juarez).
For over a century Mexico has produced some of the finest and most colorful agates to be found anywhere. The history of many of these agate localities is as colorful as the specimens themselves. With over 100 different varieties of Mexican agate currently recognized (and the list is still growing), it would be beyond the scope of this article to address them all and describe the particular characteristics of each type, but the ones discussed here are among the major varieties; thus the list can serve as an introduction to the colorful specialty of Mexican agate collecting. Mexican agates have and will continue to be ranked among the finest agates produced anywhere.
CROSS, B. L. (1996) The Agates of Northern Mexico. Burgess International Group, Edina, Minnesota, 201 pp.
FTNKELMAN, R. B., MATZKO, J. J., WOO, C. C, WHITE, J. S. Jr., and BROWN, W. R. (1972) A Scanning Electron Microscopy Study of Minerais in Geodes from Chihuahua, Mexico. Mineralogical Record, 3, 205-212.
KELLER, P. C. (1977) Geology of the Sierra del Gallego Area, Chih., Mexico. (Unpublished Ph.D. dissertation) University of Texas at Austin.
KUNZ, G. F. (1902) Gems and Precious Stones of Mexico. Transactions of the American Institute of Mining Engineers, 32, 55-93.
Table I. Localities for some important types of Mexican agate. Agate Type Latitude Longitude Agua Nueva N 29-41-53 W 106-13-11 Apache N 30-19-02 W 107-27-40 Aparejos N 29-52-22 W 106-15-13 Blue Agate N 30-35-37 W 107-01-05 Carneros N 29-33-22 W 106-10-01 Casas Grandes N 30-18-30 W 107-47-51 Coyamito N 29-46-12 W 106-13-19 Crazy Lace N 30-09-40 W 106-59-10 Derramadero N 29-49-02 W 106-14-36 Gallego N 29-49-18 W 106-21-04 Gregoria N 29-42-04 W 106-15-58 Laguna N 29-28-49 W 106-15-58 Las Choyas N 29-31-27 W 105-56-47 Loma Pinta N 30-13-34 W 106-12-58 Moctezuma N 30-15-15 W 106-14-25 Parcelas N 30-03-48 W 107-28-32 Sabinal-Guzman N 31-07-54 W 107-27-03 Santa Gertrudas N 27-46-50 W 105-39-26 Snowballs N 30-55-21 W 106-31-15 Sueco N 29-54-25 W 106-21-38
Brad L. Cross
810 East Olympic
Pflugerville, Texas 78660
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|Author:||Cross, Brad L.|
|Publication:||The Mineralogical Record|
|Date:||Nov 1, 2008|
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