Terlingua-Type Calcite, San Vicente Mine, Coahuila, Mexico


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.


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