Ulexite
Ulexite is a rare borate mineral very similar to Hydroboracite. They both commonly form as silky, fibrous crystal clusters and are not easy to distinguish. Ulexite is an interesting mineral in that is very fibrous and the fibers are transparent along their length and packed tightly together so that they act like an array of parallel glass fibers. If the material is polished perpendicular to the fiber direction, a piece of Ulexite will transmit an image from the bottom of the piece to the top. This optiacal phenomenon is the reason Ulexite has been nicknamed TV stone. Ulexite pieces are typically cut and polished only on the ends as a novelty item. Cats Eye cabochons are also available. Faceted gems are extremely rare because the material is usually too fibrous to facet.
The most notable occurances of Ulexite are Bigadiç Mine, Bigadiç, Balikesir Province, Marmara Region, Turkey; Boron Pit, U.S. Borax Mine, Boron, Kramer District, Kern County, California, USA; Anniversary Mine (Callville Wash), White Basin, Muddy Mountains District, Clark County, Nevada, USA.
| Category: | Nesoborates |
| Formula: | NaCaB5O6(OH)6·5H2O |
| hydrated sodium calcium borate hydroxide | |
| Crystallography: | Triclinic – Pinacoidal |
| Crystal Habit: | Rare as measurable crystals, which may have many forms; typically elongated to acicular, to 5 cm, then forming fibrous cottonball-like masses; in compact parallel fibrous veins, and radiating and compact nodular groups. |
| Twinning: | Polysynthetic |
| Cleavage: | [010] Perfect, [110] Perfect |
| Fracture: | Irregular, Uneven across fiber groups |
| Tenacity: | Brittle |
| Moh’s Hardness: | 2.5 |
| Density: | 1.95 – 1.96 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Colorless, White |
| Transparency: | Transparent, Translucent, Opaque |
| Luster: | Vitreous, Silky, or Satiny in fibrous aggregates |
| Refractive Index: | 1.491 – 1.520 Biaxial ( + ) |
| Birefringence: | 0.028 |
| Dispersion: | None |
| Pleochroism: | None |
