Leightonite
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| Leightonite | |
|---|---|
 | |
| General | |
| Category | Sulfate minerals |
| Formula | K2Ca2Cu(SO4)4•2H2O |
| IMA symbol | Lgh[1] |
| Strunz classification | 7.CC.70 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c |
| Identification | |
| Color | Pale blue, greenish-blue; pale blue in transmitted light. |
| Crystal habit | Lathlike crystals, flattened, elongated or equant; pseudo-orthorhombic |
| Twinning | Lamellar twinning on (100) and (010) produces pseudo-orthorhombic symmetry |
| Cleavage | None observed |
| Mohs scale hardness | 3 |
| Luster | Vitreous |
| Diaphaneity | Transparent, translucent |
| Specific gravity | 2.95 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.578 nβ = 1.587 nγ = 1.595 |
| Birefringence | δ = 0.017 |
| References | [2][3] |
Leightonite is a rare sulfate mineral with formula of K2Ca2Cu(SO4)4•2H2O.[3]
Leightonite forms flattened to elongated bladed crystals of variously interpreted crystal structure. Its crystal system is reported as triclinic morphologically, but also as pseudo-orthorhombic due to intricate lamellar twinning that mimics orthorhombic symmetry.[2][3] Because it is triclinic, the crystal is represented by a system of three unequal vectors with corresponding unequal angles between them.