New Mexico Mineral Symposium — Abstracts

Arizona certainly contains its share of potential calcite-producing geology. The northern third of the state consists of the Colorado Plateau and contains exposed layers of limestone hundreds of feet thick. As one moves south, limestone beds are not only exposed in the mountain ranges and valleys, but a few of the layers play host to some of the richest copper mines in the world. Whereas Arizona is not known for large watercourses of calcite crystals similar to those found in the Tri-State area, there are a number of localities that have produced distinctive and brightly colored calcite crystals. The specimen colors range from colorless and white to black and virtually every hue in between.

The journey starts at Arizona's newest state park, the Kartchner Caverns. The caverns were discovered in the mid-1970s by two avid cave explorers. They managed to keep their discovery secret for a number of years. When it became obvious that the word was beginning to leak out, they went to the Kartchner family, who owned the land where the caverns are located and made them aware of their discovery. Together, they decided the caverns should be preserved for the benefit of the State of Arizona, and negotiations began with the State Parks Department. After an extended design and construction period, the first part of the caverns was opened to the world in 1999. The formations are great, but even more spectacular is the effort to preserve the interior in a pristine condition—with more effort to come.

Next on the journey are the great copper mines of Bisbee. In the early days of mining at this location, the miners learned that one of the ways to find orebodies was to look for caverns. When the sulfide minerals oxidized, the total volume decreased, which left a void above the oxide zones. Because the sulfide mineralization was emplaced in limestone beds, open voids were left in which calcite and aragonite could form. Some of the percolating waters moved through copper minerals, so not only were white calcite crystals formed but also a number of pale-blue and green formations resulted. Over the years of copper mining, a number of watercourses were encountered in many of the mines. These produced some very distinctive specimens, including the iron-stained, hexagonal, "poker-chip" style crystals. Of course, the most desirable of the Bisbee calcites are those colored bright red and bright green by included cuprite and malachite, respectively.

In spite of a lot of mining activity in the eastern fourth of the state, there is a dearth of good calcite localities. One has to travel back to the central part of the state to the copper mines of Globe–Miami, Superior, Ray, and San Manuel to find collectible calcites. The Old Dominion mine in Globe produced white calcites, and while not colorful, the contrasting matrix makes for pleasing specimens. The calcite crystals occur on chrysocolla-stained drusy quartz pockets and on just plain chrysocolla. There are cuprite included calcites that come from here as well.

The Magma mine at Superior produced small pockets of calcites throughout its history. It is much more famous for its barites and pyrites, so the calcites have been somewhat overlooked. The calcites range from pink manganocalcites (collected at the bottom of number 5 shaft in 150° water) to a number of white and off-white specimens of various crystal shapes. The best single pocket of calcites ever collected at the Magma mine was discovered in one of the drift headings in the fall of 1986. A pocket approximately 5 ft long by 1 ft wide and 4 ft high was discovered that contained clear, twinned crystals up to 3 inches across sitting on a dark crystallized matrix.

The copper mine at Ray (now called Kearny because the town of Ray has long since become part of the open pit) has produced a number of nice calcite specimens over the years. The best pocket consisted of yellow calcite crystals with cuprite inclusions. Within the past two years, a large quantity of chrysocolla was mined, which included vugs with white calcite crystals. Although these aren't colorful calcites per se, it is a truly colorful association.

San Manuel is a large, underground copper mine about 50 mi north of Tucson. Unlike some of the other great copper deposits that were deposited in limestone beds, this orebody is a porphyry. There are a number of small cracks and openings in the rock mass that have allowed calcite crystals to grow. While not on a caliber with the Magma mine or the Ray mine, they are interesting nonetheless. Some occur with associated gypsum or pyrite crystals.

Continuing south and to the west is the copper mine at Ajo. The New Cornelia mine has a long history and has produced some of the reddest cuprite-included calcite crystals in the state. It is best known for its crystallized coppers and azurite and malachite specimens; however, it is one of the finest localities for red calcite crystals.

Before heading north one last time, the Red Cloud mine should at least be mentioned. The major gangue mineral in the vein is brown calcite. Whereas a number of localities in Arizona contain this dark-brown calcite, the Red Cloud is the only place a collector might want one of these specimens—particularly if there are wulfenites scattered across the calcite. Otherwise, they are the ugliest calcite crystals I have collected.

Leaving the Red Cloud, there are three localities left that are noteworthy. The Bruce mine at Bagdad produced colorless to white, highly lustrous crystals that display fishtail twinning up to 3 inches long. Unfortunately, the miners broke the larger twins off, so it is unusual to have a specimen with twins over 1¹/₂ inches long still on matrix. The same thing occurred in the initial collecting at the Brushy Creek mine in Missouri when the watercourse with the gray calcites and iridescent marcasite was encountered.

Heading east and down into the Verde Valley, a locality known to any rockhound or mineral collector in Arizona is the Salt mine. It was the second locality I ever went to, and I still direct people to the area to collect. It is known for its calcite after glauberite pseudomorphs, along with gypsum after glauberite, aragonite after glauberite, and just plain glauberite crystals.

The last locality of our journey is in Mohave County in western Arizona. A vein of calcite crystals was discovered that is more typical of English crystallization than any other Arizona locality. The locality produced specimens from the size of thumbnails to the size of a large cabinet, with crystals in excess of an inch. The collecting ended when the area changed ownership and the vein got too deep.