Mineral Species: Ulexite after Borax 

Chemical Formula: NaCaB5O6(OH)6-5H2O

Chemical Name: Hydrated Sodium Calcium Borate Hydroxide

Mineral Class: Borate

Mineral Notes: Ulexite, like other borates, is structurally complex, having a basic structure of sodium, water and hydroxide octahedrons linked in endless chains. The chains are cross-linked by boron units which have a formula of B5O6(OH)6 and composed of three borate tetrahedrons and two borate triangular groups. Ulexite is found with Borax and is directly deposited in arid regions from the evaporation of water in periodic lakes called playas. Specimens of ulexite may form a "cotton ball" tuft of acicular crystals, often confused with Okenite. Ulexite is also found in a vein-like bedding habit composed of closely-packed fibrous crystals. This variety is called "TV Rock" because of an unusual optical phenomenon. The fibers behave like optical fibers and transmit an image from one side of the specimen to the other.

Description: Two large, white, twinned crystals of Ulexite replacing Borax. Both crystals show excellent form. However one is clearly monoclinic as in Borax, whilst the other is triclinic as in Ulexite. Both have good pyramidal terminations. An interesting mineral oddity.

Location: Boron, Kern Co., California, USA.