Ikaite
Ikaite is the mineral name for the hexahydrate of calcium carbonate, CaCO3·6H2O. Ikaite tends to form very steep or spiky pyramidal crystals, often radially arranged, of varied sizes from thumbnail size aggregates to gigantic salient spurs. It is only found in a metastable state and decomposes rapidly by losing most of its water content once removed from near-freezing water. This "melting mineral" is more commonly known through its pseudomorphs.
| Ikaite | |
|---|---|
Calcite after ikaite var. glendonite concretion | |
| General | |
| Category | Carbonate mineral, hydrous carbonates subgroup |
| Formula (repeating unit) | CaCO3·6H2O |
| IMA symbol | Ika |
| Strunz classification | 5.CB.25 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c |
| Identification | |
| Color | White when pure |
| Crystal habit | Nearly square prism; pyramidal; sigmoidal: square prism capped with oppositely canted pyramids; massive, tubular (tinolite vr.) |
| Mohs scale hardness | 3 |
| Luster | Dull |
| Streak | White |
| Specific gravity | 1.83 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.455 nβ = 1.538 nγ = 1.545 |
| Birefringence | d = 0.090 |
| Other characteristics | Decomposes into water and calcite above 8 °C |
| References | |
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