Huntite
| Huntite | |
|---|---|
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | Mg3Ca(CO3)4 |
| Strunz classification | 05.AB.25 |
| Dana classification | 14.04.03.01 |
| Crystal symmetry |
Trigonal trapezohedral H-M symbol (3 2) Space group: R 32 |
| Unit cell | a = 9.505 Å, c = 7.821 Å; Z=3 |
| Identification | |
| Formula mass | 353 |
| Color | White, lemon white |
| Crystal habit | Platy crystals; compact chalklike masses |
| Crystal system | Trigonal |
| 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 | [1][2][3] |
Huntite is a carbonate mineral with the chemical formula Mg3Ca(CO3)4.[3] The earliest known reference to huntite is a paper by George Faust[4] from 1953 in which the discovery of a new mineral in Nevada was announced. Faust acknowledges that the mineral probably had been discovered previously but had been misidentified as impure magnesite by W. E. Ford in 1917. Faust announced that the new mineral was to be named huntite in honour of his former teacher, Walter Frederick Hunt (1882–1975), Professor of Petrology at the University of Michigan from 1922 until 1933 and editor of American Mineralogist for 35 years.[5] Faust carried out analysis of the newly discovered mineral, huntite, discovering that it went through two endothermic decompositions which were attributed to the dissociation of MgCO3 and CaCO3 respectively. He showed that the chemical formula for huntite was Mg3Ca(CO3)4.
Huntite often occurs in combination with hydromagnesite. Mixed reserves of these minerals are known in Turkey and Greece and commercially exploited for their 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.[6][7][8]
Uses
Its most common industrial use is in a natural mixture with hydromagnesite as a flame retardant or fire retardant additive for polymers.[9][10][11] The heat of a fire will cause huntite to decompose releasing carbon dioxide into the flames. This helps to slow the spread of the fire. The release of carbon dioxide is endothermic, meaning that it takes in heat, this action helps to cool the burning material, again slowing the spread of the fire. These types of mixtures are used as alternatives to the more commonly used aluminium hydroxide.
References
- ↑ Handbbok of Mineralogy: Huntite
- ↑ Huntite on Mindat.org
- ↑ 3.0 3.1 Huntite on Webmineral
- ↑ Faust, GT (1953). "Huntite A New Mineral". American Mineralogist 38: 4–24.
- ↑ Ramsdell, LS (1958). "Presentation of the Roebling Medal to Walter F Hunt". American Mineralogist 43: 334–335.
- ↑ Ozao, R; Otsuka, R. (1985). "Thermoanalytical Investigation of Huntite". Thermochimica Acta 86: 45–58. doi:10.1016/0040-6031(85)87032-5.
- ↑ Hollingbery, LA; Hull TR (2010). "The Thermal Decomposition of Huntite and Hydromagnesite - A Review". Thermochimica Acta 509 (1-2): 1–11.
- ↑ Hollingbery, LA; Hull TR (2012). "The Thermal Decomposition of Natural Mixtures of Huntite and Hydromagnesite". Thermochimica Acta 528: 45–52.
- ↑ Hollingbery, LA; Hull TR (2010). "The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review". Polymer Degradation and Stability 95 (12): 2213–2225.
- ↑ Hollingbery, LA; Hull TR (2012). "The Fire Retardant Effects of Huntite in Natural Mixtures with Hydromagnesite". Polymer Degradation and Stability 97 (4): 504–512.
- ↑ Hull, TR; Witkowski A, Hollingbery LA (2011). "Fire Retardant Action of Mineral Fillers". Polymer Degradation and Stability 96 (8): 1462–1469.