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Terlingua Calcite, a Beautiful Rock of Many Faces

23.8.2019

Terlingua calcite is a rock of many faces, as few other fluorescent minerals show such a varied fluorescent response under different UV wavelengths.  It is one of the most spectacular and beautiful fluorescent minerals due to its bright, multi-colored, multi-wave, fluorescent response, and bright, persistent phosphorescence.  By definition, it is a variety of the mineral calcite that was found in the area of Terlingua, Texas, that shows bright blue/white fluorescence under short wave UV (254nm), with bright and lasting blue phosphorescence; lavender fluorescence under mid wave UV (302nm), with blue phosphorescence similar to that seen after short wave, but not as bright; and lastly, bright pink fluorescence under long wave UV (365nm), sometimes accompanied by brief, dim phosphorescence.  The specimen featured here is an exceptional example of Terlingua calcite due to its large size and spectacular fluorescence.  In addition, the two main sides of this specimen show a dramatically different series of responses under UV.  The following photo montage shows the many faces of this specimen under various UV wavelengths and visible light, front side and back. 

The photo montage, above, shows the front and back faces of the specimen under visible light, short wave UV, mid wave UV and long wave UV.  The majority of the calcite is exposed on the front side of the piece, while the back side is dominated by chalcedony, aragonite and a non-fluorescent red/brown matrix.

Full view of the front side of the specimen, seen under visible light.  Note the pink zones internal to the cleavage faces.  These zones are often present in Terlingua calcite and generally correspond to to the areas of brightest fluorescence.  This specimen measures 6.5 x 5.5 x 3.5 inches, and weighs 5.1 pounds.

Front side of the specimen showing bright blue/white fluorescence under short wave UV.  Note the triangular zones of bright fluorescence, another characteristic typical for Terlingua calcite.  The areas of green fluorescence seen along the upper left and right edges are caused by uranyl-activated chalcedony.

Bright and long-lasting blue phosphorescence/afterglow following exposure to short wave UV.  This is another characteristic typical of Terlingua calcite.

As shown in the above photograph, many specimens of Terlingua calcite show a lavender-colored fluorescent response under mid wave UV.

Following exposure to mid wave UV, blue phosphorescence/afterglow is seen, although not as bright or long-lasting as after exposure to short wave UV.

As shown in the image above, one of the most striking characteristics of Terlingua calcite is the bright pink fluorescence seen under long wave UV.  Similar to the responses seen under short and mid wave UV, note the bright triangular zones of fluorescence.

As can be seen in the above photograph of the same specimen, some Terlingua calcite displays brief, dim, phosphorescence/afterglow following exposure to long wave UV.  To the naked eye, this response appears as a dim, very short-lived, ghostly white glow after the long wave lamp is turned off.

The reverse side of this specimen is nearly as interesting as the front, and has a more varied mineral presentation.  As seen in the photograph above, taken under visible light, this side is dominated by areas of light-colored chalcedony and aragonite, and a red/brown non-fluorescent matrix.  Small patches of calcite are visible in the lower left and right corners of the piece.

As seen in the above photograph, the back side of this specimen shows a completely different assemblage of fluorescent colors under short wave UV compared with the front.  Uranyl-activated chalcedony shows a bright green response, while the aragonite fluoresces a softer pale blue.  Several patches of Terlingua calcite, visible along the lower edge of the piece, add bright blue/white fluorescent accents.

After the short wave source is shut off, blue phosphorescence/afterglow is seen over the majority of the specimen.

Under mid wave UV, the chalcedony glows a more pale green color, while the aragonite shows a brighter cream/white response.  Patches of other minerals, possibly calcite, fluoresce various shades of orange.  The Terlingua calcite shows the typical lavendar fluorescence.

In the above photograph, taken under long wave UV, the chalcedony and aragonite both show a similar pale blue/white fluorescent response, while the patches of Terlingua calcite show characteristic bright pink fluorescence.

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