Hydromagnesite
| Hydromagnesite | |
|---|---|
Hydromagnesite balloon in Jewel Cave
|
|
| General | |
| Category | Carbonate mineral |
|
Formula (repeating unit) |
Mg5(CO3)4(OH)2·4H2O |
| Strunz classification | 5.DA.05 |
| Dana classification | 16b.07.01.01 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/c |
| Identification | |
| Formula mass | 467.64 g/mol |
| Color | Colorless, white |
| Crystal habit | Acicular and as encrustations; pseudo-orthorhombic |
| Twinning | Polysynthetic lamellar on {100} |
| Cleavage | {010} Perfect, {100} Distinct |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 3.5 |
| Luster | Vitreous, silky, pearly, earthy |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.16 - 2.2 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.523 nβ = 1.527 nγ = 1.545 |
| Birefringence | δ = 0.022 |
| Ultraviolet fluorescence | Fluorescent, short UV=green, long UV=bluish white. |
| References | |
Hydromagnesite is a hydrated magnesium carbonate mineral with the formula Mg5(CO3)4(OH)2·4H2O.
It generally occurs associated with the weathering products of magnesium containing minerals such as serpentine or brucite. It occurs as incrustations and vein or fracture fillings in ultramafic rocks and serpentinites. It occurs in hydrothermally altered dolomite and marble. It commonly appears in caves as speleothems and "moonmilk", deposited from water that has seeped through magnesium rich rocks. It is the most common cave carbonate after calcite and aragonite. It thermally decomposes, over a temperature range of approximately 220 °C to 550 °C, releasing water and carbon dioxide leaving a magnesium oxide residue.
It was first described in 1836 for an occurrence in Hoboken, New Jersey.
Stromatolites in an alkaline (pH greater than 9) freshwater lake (Salda Gölü) in southern Turkey are made of hydromagnesite precipitated by diatoms and cyanobacteria.
Microbial deposition of hydromagnesite is also reported from playas in British Columbia. The hydromagnesite-magnesite playas near Atlin, British Columbia are some of the most studied deposits of hydromagnesite. These deposits have been characterized in the context of a biogeochemical model for CO2 sequestration.
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