Huntite
| Huntite | |
|---|---|
Huntite
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| General | |
| Category | Carbonate mineral |
|
Formula (repeating unit) |
Mg3Ca(CO3)4 |
| Strunz classification | 5.AB.25 |
| Dana classification | 14.04.03.01 |
| Crystal system | Trigonal |
| Crystal class | Trapezohedral (32) H-M symbol: (3 2) |
| Space group | R32 |
| Unit cell | a = 9.505 Å, c = 7.821 Å; Z = 3 |
| Identification | |
| Formula mass | 353 g/mol |
| Color | White, lemon white |
| Crystal habit | Platy crystals; compact chalklike masses |
| Fracture | Subconchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 1-2 |
| Luster | Earthy (dull) |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 2.696 |
| Optical properties | Uniaxial (–) |
| Refractive index | nω = 1.622 nε = 1.615 |
| References | |
Huntite is a carbonate mineral with the chemical formula Mg3Ca(CO3)4. Huntite crystallizes in the trigonal system and typically occurs as platy crystals and powdery masses.
In 1953 a paper by George Faust announced the discovery of a new carbonate mineral found in Currant Creek, Nevada (US). Faust acknowledged that the mineral probably had been discovered previously, but it had been misidentified as impure magnesite by W. E. Ford in 1917. Faust named the new mineral "huntite" in honour of his former teacher, Walter Frederick Hunt (1882–1975)[14] , Professor of Petrology at the University of Michigan. Faust carried out analyses of the mineral, and found amongst others that in differential thermal analysis huntite showed two endothermic peaks, which could be attributed to the dissociation of MgCO3 and CaCO3 respectively. Chemical analyses showed huntite to consist of Mg3Ca(CO3)4.
Huntite often occurs in combination with other Mg/Ca carbonates such as dolomite, magnesite, and hydromagnesite. Large deposits of huntite occur in Turkey and Greece and these are commercially exploited because of its fire retardant properties. Huntite thermally decomposes over a temperature range of about 450–800 °C, releasing carbon dioxide and leaving a residue of magnesium and calcium oxides.
Huntite has been found in a variety of environments. For example it occurs in the modern carbonate sediments of the tidal flats bordering the Persian Gulf, in seasonal salt lakes of Turkey, in various playa lakes of British Columbia (Canada), in lacustrine deposits of Greece and in modern sabkha sediments in Tunisia.
Caves seem to be well suited for the low-temperature formation of huntite. For example it has been reported from the caves of the Carlsbad Caverns National Park, New Mexico (USA); in the Castleguard Cave (Alberta, Canada); in the Grotte de la Clamouse, France; in various caves of the Transvaal Province of South Africa; in the Jenolan Caves, Australia; and in the Castañar Cave near Cáceres, Spain.
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Wikipedia