Ulexite
| Ulexite | |
|---|---|
Ulexite from California (size: 6.9 × 5 × 3.1 cm)
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| General | |
| Category | Nesoborates |
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Formula (repeating unit) |
NaCaB5O6(OH)6·5H2O |
| Strunz classification | 6.EA.25 |
| Dana classification | 26.05.11.01 |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal (1) (same H-M symbol) |
| Space group | P1 |
| Unit cell | a = 8.816(3) Å, b = 12.87 Å c = 6.678(1) Å; α = 90.25° β = 109.12°, γ = 105.1°; Z = 2 |
| Identification | |
| Color | Colorless to white |
| Crystal habit | Acicular to fibrous |
| Twinning | Polysynthetic on {010} and {100} |
| Cleavage | Perfect on {010} good on {110} poor on {110} |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 2.5 |
| Luster | Vitreous; silky or satiny in fibrous aggregates |
| Streak | White |
| Diaphaneity | Transparent to opaque |
| Specific gravity | 1.95 – 1.96 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.491 – 1.496 nβ = 1.504 – 1.506 br/>nγ = 1.519 – 1.520 |
| Birefringence | δ = 0.028 |
| 2V angle | Measured: 73° to 78° |
| Ultraviolet fluorescence | Depending on fluorescent impurities, ulexite may fluoresce yellow, greenish yellow, cream, white under short waves and long waves UV |
| Solubility | Slightly soluble in water |
| Other characteristics | Parallel fibrous masses can act as fiber optical light pipes |
| References | |
Ulexite (NaCaB5O6(OH)6·5H2O) (hydrated sodium calcium borate hydroxide), sometimes known as TV rock, is a mineral occurring in silky white rounded crystalline masses or in parallel fibers. The natural fibers of ulexite conduct light along their long axes, by internal reflection. Ulexite was named for the German chemist Georg Ludwig Ulex (1811–1883) who first discovered it.
Ulexite is a structurally complex mineral, with a basic structure containing chains of sodium, water and hydroxide octahedra. The chains are linked together by calcium, water, hydroxide and oxygen polyhedra and massive boron units. The boron units have a formula of [B5O6(OH)6]3– and a charge of −3. They are composed of three borate tetrahedra and two borate triangular groups.
Ulexite is found in evaporite deposits and the precipitated ulexite commonly forms a "cotton ball" tuft of acicular crystals. Ulexite is frequently found associated with colemanite, borax, meyerhofferite, hydroboracite, probertite, glauberite, trona, mirabilite, calcite, gypsum and halite. It is found principally in California and Nevada, US; Tarapacá Region in Chile, and Kazakhstan. Ulexite is also found in a vein-like bedding habit composed of closely packed fibrous crystals.
Ulexite is also known as TV rock due to its unusual optical characteristics. The fibers of ulexite act as optical fibers, transmitting light along their lengths by internal reflection. When a piece of ulexite is cut with flat polished faces perpendicular to the orientation of the fibers, a good-quality specimen will display an image of whatever surface is adjacent to its other side (as shown in the photograph).
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Wikipedia