ulexite

noun

1. a mineral, hydrous sodium and calcium borate, NaCaB5O9⋅8H2O, occurring in arid regions in the form of white acicular crystals: a major source of borax.

1. A white triclinic mineral that forms rounded, reniform (kidney-shaped) masses of very fine needle-shaped crystals. Ulexite has the unusual optical property of projecting an image of an object placed against a transverse section of it to the opposite surface. It is usually associated with borax deposits and is found in arid environments. Chemical formula: NaCaB5O9·8H2O.