Oct 11 at 1:48 PM
COLLECTABLE MINERALS OF THE TERLINGUA AREA
Collectable Minerals of the Terlingua Cinnabar District and surrounding area.
Copyright 2013 by Fred Gossien
Due to be published December, 2013
1. Cinnabar - Small specimen-grade cinnabar is still found in some mine tailings. Larger ore-grade pieces are very rare. Large cinnabar crystals, such as those currently coming from China, never existed in the district.
2. Terlingua Calcite - Terlingua Calcite is defined as that which fluoresces a strong blue with exposure to shortwave ultraviolet light (UV), with long-lasting phosphorescence, and under longwave UV fluoresces pink without phosphorescence. It is usually, but not always, pink in color and is a "must have" for fluorescent mineral collectors worldwide. Calcite not meeting the fluorescent/phosphorescent definition would be called "calcite from Terlingua," not Terlingua Calcite. For more information go to http://www.terlinguacalcite.com/.
3. Other calcites - Calcite occurs in more crystal forms than any other mineral, with a dozen or more found in the area (I've never counted). Many of these are of sufficient size and quality for most mineral collections.
4. Fluorite - Small fluorite cubes and plates of cubes are found near several mines or prospects, rarely over about 1/4" on edge. They are mostly a muddy yellow color though some water clear and milky white specimens occur. Most rare are very tiny purple cubes found at a remote prospect.
5. Quartz - In the vicinity of cinnabar mines quartz crystals are extremely rare. A small number of tiny double-terminated crystals have been found perched on calcite at only two locations, never associated with either cinnabar or Terlingua Calcite. Tiny bright green fluorescing chalcedony balls (a form of quartz) are, however, occasionally seen on the surface of Terlingua Calcite. Quartz, calcite and chalcedony geodes up to about a foot in diameter have been found in some intrusions and lava flows in the area. Some amethyst and slightly smoky quartz have also been found.
6. Opal - Small chunks of common opal were found some 15-20 miles north of the district, scattered over an area of about 1/2 square mile. Most are milky white but some are shades of blue, tan and grey. Most of the white pieces fluoresce bright green under shortwave UV due to trace amounts of uranium.
7. Analcime, natrolite and stilbite - In late 2001 in a small pocket near the southwest fringe of the district notable crystals of these minerals were found. Analcime (with an unmistakable 24-sided crystal structure) was known only to about 5 mm in diameter (about 3/16") while specimens from the pocket exceeded 50 mm (over 2"); perfect natrolite crystals to over 3" were found, far larger than was previously known, and stilbite, previously unknown in the area, was found as 4-5 mm crystal clusters on, and in the matrix around, analcime crystals.
8. Apophilite - About a mile from the analcime site, masses of white pseudo-rectangular crystals, individual crystals to nearly an inch, were found in vugs up to about 2 feet in diameter. These were later determined to be one of the three recognized varieties of apophilite, the exact variety still unknown.
9. Terlingua marbles - These are the Terlingua equivalent to Utah's famous Moqui marbles which are now illegal to collect. They were found scattered over a large area some 20 miles north of Terlingua and are mostly limonite, not a distinct mineral but a term describing various iron oxides of indefinite composition, resulting from altered pyrite. The shiny black crystals on some marbles are probably specular hematite.
10. Petrified wood - More correctly called fossilized wood, it occurs throughout the region, mostly in very scattered localized concentrations. It is commonly in rather drab shades of brown or grey but colorful agatized pieces are sometimes found. It can sometimes be found in Terlingua Creek and Rough Run.
Note: Several other minerals occur and are discussed in the complete text of this publication, along with greatly expanded versions of the above minerals. The additional minerals include barite, gypsum, aragonite, garnet, pectolite, vanadinite and several iron oxides.
Caution: Remember that all land in the region is private property except the state and national parks (where collecting is illegal). Get permission before trespassing. Also, rattlesnakes and dehydration are out there waiting for you. Be careful! Use common sense! Have fun!