Howlite
Howlite, a calcium borosilicate hydroxide (Ca2B5SiO9(OH)5), is a borate mineral found in evaporite deposits.
| Howlite | |
|---|---|
| General | |
| Category | Inoborates |
| Formula (repeating unit) | Ca2B5SiO9(OH)5 |
| IMA symbol | How |
| Strunz classification | 6.CB.20 |
| Dana classification | 25.3.5.1 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/c |
| Unit cell | a = 12.82 Å, b = 9.351(1) Å c = 8.608(2) Å; β = 104.84(2)°; Z = 4 |
| Identification | |
| Color | White, colorless |
| Crystal habit | Massive to nodular, occurs as tabular prisms flattened parallel to [100] |
| Cleavage | None |
| Fracture | Conchoidal, uneven |
| Mohs scale hardness | 3.5 |
| Luster | Subvitreous, glimmering |
| Streak | white |
| Diaphaneity | Translucent |
| Specific gravity | 2.53 – 2.59 |
| Optical properties | Biaxial (−), colorless (transmitted light) |
| Refractive index | nα = 1.583 – 1.586 nβ = 1.596 – 1.598 nγ = 1.600 |
| Birefringence | δ = 0.017 |
| 2V angle | 73° |
| References | |
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