New Mexico Mineral Symposium — Abstracts

Anatase has been reported from several localities in Colorado, but it wasn't until July 1984 that microcrystals of the mineral were discovered in the San Juan Mountains of southwestern Colorado. Robert Stoufer and the author made the first discovery high above the scenic town of Ouray in the abandoned workings of the Ores and Metals mine located in Squaw Gulch. The crystals, which vary in color from brilliant blue-black to translucent zoned crystals of light yellow or blue to blue black, range up to 0.5 mm and are perched on small transparent quartz crystals.

The next discovery of micro anatase crystals was in the underground workings of the Mountain Monarch mine, Ouray County, in 1985 by Richard Dayvalut. The 1-mm crystals, which are semitransparent and bluish-gray in color, show a prominent basal pinacoid and are associated with crystallized quartz, chalcopyrite, rhodochrosite, barite, and hubnerite.

In summer 1991, the author discovered anatase along with brookite and rutile on the dumps of the Silver Link mine in Ouray County. The crystals range up to 0.7 mm in size and exhibit two crystal forms. The dipyramidal crystals show a subtransparency and are color zoned from dark yellowish-green to dark greenish-blue, whereas crystals with a dominant basal pinacoid are typically dark bluish-black. The anatase occurred on quartz associated with crystallized brookite, bornite, chalcopyrite, and rutile.

Collecting on the dumps of the Grizzly Bear mine in Ouray County by Dorothy Atlle and Dee Rickey in summer 1994 produced a few tiny (0.1-mm) smoky-gray crystals of anatase associated with pale brown crystals of brookite.

In fall 1994, while collecting on the dumps of the Silver Mountain (concave tunnel), Indiana, Topeka, and Kentucky Giant mines, the author noted the widespread presence of anatase and brookite on all of the mine dumps. Anatase collected from the various mine dumps occurred in a variety of colors, ranging from honey-yellow to dark brown and from pale blue to very dark blue. The most common crystal habit is the steep dipyramids. Brookite occurred as honey-yellow to medium brown tabular crystals that range up to 0.5-mm in size. Rutile occurred as lathlike, pale-brown crystals up to 0.1 mm that crystallized on either brookite or quartz crystals.

In summer 1998 Robert Stoufer collected dark-blue to black anatase partially embedded on the faces of quartz crystals that occurred in the Leadville limestone in the amphitheater in Ouray. The crystals are unusual in that they occur in quartz veins in a sedimentary formation rather than a poly-metallic fissure vein enclosed in San Juan Tuff.

The last occurrence noted in the San Juan Mountains was a single anatase crystal found by Dee Rickey and Ron Gibbs at the Bandora mine in San Juan County. Recently in a restudy of the base-metal replacement ores of the Camp Bird mine, a single greenish crystal of anatase was noted associated with crystallized quartz, epidote, and pyrite.