Colemanite, an Interesting Fluorescent Borate Mineral

This post features a large specimen of well-crystallized colemanite from Boron, Kern County, California.  This piece shows a bright multi-wavelength fluorescent and phosphorescent response under UV.  This size of this specimen is 15 x 11 x 8 cm and it weighs 914 grams.


Colemanite is a hydrated calcium borate mineral that forms in evaporite deposits of alkaline lake beds.  In addition to its fluorescence, colemanite is also a pyroelectric material, meaning that it develops an electrical charge potential in response to changes in temperature.

As shown in the photo montage above, the colemanite shows a ghostly blue/white fluorescent response under short wave UV (254 nm) followed by blue phosphorescence.  A slightly warmer white fluorescent response is seen under long wave UV (365 nm) with green phosphorescence following.

Same specimen, shown under visible light.

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