Terlingua-type calcite shows a similar response to UV light compared to true Terlingua calcite, from the Terlingua, Texas, area. True Terlingua calcite shows bright blue fluorescence under short wave UV, with bright and long-lasting phosphorescence. Under long wave UV, the fluorescent response is bright pink. True Terlingua calcite comes from only one source however- the mercury mines of Terlingua, Brewster County, Texas. Calcite showing a similar fluorescent response, but collected from other locations, is referred to as “Terlingua-type” calcite. Due to mine closures and reclamation, true Terlingua calcite has become increasingly difficult to collect and is therefore somewhat scarce. However, Terlingua-type calcite from various locations is still relatively abundant and easy to obtain.
This is a specimen of Terlingua-type calcite, from the San Vicente Mine, Boquillas Del Carmen, Coahuila, Mexico. Much of the Terlinga-type calcite from Coahuila, Mexico, has been treated with hydrochloric acid, creating a smooth, rounded, surface. Although the acid-treatment affects the surface appearance of the calcite, it does not affect the fluorescent properties of the mineral. Though cosmetically altered, these Mexican Terlingua-type calcites provide spectacular fluorescent specimens. The size of this specimen of Terlingua-type calcite is 6.6 x 5.1 x 5.0 cm.