Hydrohalite
From Wikipedia, the free encyclopedia
Hydrohalite is a halide mineral that occurs in saturated halite brines at cold temperatures (below 0.1 °C) and is the most common form of hydrated sodium chloride. It was first described in 1847 from an occurrence in Dürrnberg, Austria.
| Hydrohalite | |
|---|---|
| General | |
| Category | Halide mineral |
| Formula | NaCl·2H2O |
| IMA symbol | Hhl[1] |
| Strunz classification | 3.BA.05 |
| Dana classification | 9.1.2.1 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/c |
| Identification | |
| Colour | Colourless or white |
| Diaphaneity | Transparent |
Physical properties
Hydrohalite has a high nucleation energy, it decomposes at 0.1°C, giving a salty brine and solid halite.
The cryohydric point of hydrohalite is at −21.2 °C (−6.2 °F), solutions will normally need to be supercooled for crystals to form. Above this temperature, liquid water saturated with salt can exist in equilibrium with hydrohalite. Unlike halite, hydrohalite has a strong positive temperature coefficient of solubility.[2] Under pressure, hydrohalite is stable between 7,900 and 11,600 atmospheres pressure. The decomposition point increases at the rate of 0.007K per atmosphere (for 1–1000 atmospheres),[2] reaching a maximum decomposition temperature is at 25.8°C around 9400 atmospheres. The decomposition temperature reduces again at higher pressures.[2]