Ulexite is a naturally occurring borate mineral that forms in evaporite deposits such as dry lake beds in the Western US, the Atlantic Provinces of Canada, the high deserts of Chile, and other locations. It can occur in the form of a puff-ball with needle-like crystals radiating from a central point or as massive blocks of near-transparent material. This specimen is particularly large at ~10.5 x 4 x 2 inches and 2.2 pounds, and it clearly demonstrates the fiber-optic type phenomenon for which ulexite is known. This is because the mineral structure forms fine, twinned, needle-like crystals that are regularly aligned with each other. Light entering a crystal at one end is internally reflected through the length of the crystal and emerges from the other end in essentially the same direction as it entered. The effect is that an image place under a polished slab of ulexite will be transmitted to the top polished surface with surprising integrity. Impurities, cracks, and other structural defects in the specimen will compromise the image quality. See photo for example. Note that ulexite is soluble in water and the surface can be damaged if cleaned with a water-based liquid (so don't do that).Date: Country (if not USA): State: City: Provenance: William Mayrsohn Collection