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. For most of recorded history its main use was as a white pigment.John Clarke, "Two Aboriginal Rock Art Pigments from Western Australia: Their Properties, Use, and Durability." Studies in Conservation, Volume 21, Issue 3 (1976) pp. 134–142 https://doi.org/10.1179/sic.1976.023Richard Parkinson, The Painted Tomb-Chapel of Nebamun: Masterpiece of Ancient Egyptian Art in the British Museum (The British Museum Press: London, 2008) page 50 Today the most common industrial use of huntite is as a natural mixture with hydromagnesite as a flame retardant or fire retardant additive for polymers.
Discovery 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),Kraus, E.H., American Mineralogist, v. 38, Jan–Feb, 1953 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.
Properties 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.
Occurrences 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,Kinsman, D. J. J. (1967): Huntite from a carbonate – evaporite environment. American Mineralogist, vol. 52, pp. 1332–1340. in seasonal salt lakes of Turkey,Irion, G. & Müller, G. (1968): Huntite, dolomite, magnesite and polyhalite of Recent age from Tuz Gölü, Turkey. Nature, vol. 220, pp. 1309–1310.Irion, G. (1970): Mineralogisch-sedimentpetrographische und geochemische Untersuchungen am Tuz Gölü (Salzsee). Chemie der Erde, vol.29, pp. 163–226.Camur, M. Z. & Mutlu, H. (1996): Major-ion geochemistry and mineralogy of the Salt-Lake (Tuz Gölü) basin, Turkey. Chemical Geology, vol.127, pp. 313–329.Mutlu, H.; Kadir, S. & Akbulut, A. (1999): Mineralogy and water chemistry of the Lake Acigöl, Denizli, Turkey. Carbonates and Evaporites, vol. 14, pp. 191–199. in various playa lakes of British Columbia (Canada),Renaut, R. W. (1990): Recent carbonate sedimentation and brine evolution in the saline lake basins of the Cariboo Plateau, British Columbia, Canada. pp. 67–81, in: Comin, F. A. & Northcote, T. G. (eds.): Saline Lakes. Kluwer, Dordrecht. in lacustrine deposits of GreeceWetzenstein, W. (1974): Sedimentpetrographische Untersuchungen an limnischen Magnesit – Huntitlagerstätten im Plio-Pleistozän des Serviabeckens / Nordgriechenland. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte, 1974, pp. 625–642. and in modern sabkha sediments in Tunisia.Perthuisot, J. P. (1971): Présence de magnésite et de huntite dans le sebkha el Melah de Zarzis. Comptes Rendus des Séances de l'Académie des Sciences de Paris, Série D, vol. 272, pp. 185–188. Perthuisot, J. P. (1974): Les dépôts salins de la sebkha El Melah de Zarzis: Conditions et modalités de la sédimentation évaporitique. Revue de la geographie physique et de géologie dynamique, vol. 16, pp. 177–187.
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 (US);Thrailkill, J. (1971): Carbonate deposition in Carlsbad caverns. Journal of Geology, vol. 79, pp. 683–695.Hill, C. A. (1973): Huntite flowstone in Carlsbad Caverns, New Mexico. Science, vol. 181, pp. 158–159.Gonzalez, L. A. & Lohmann, K. C. (1988): Controls on mineralogy and composition of spelean carbonates: Carlsbad Caverns, New Mexico. pp. 81–101, in: James, N. P. & Choquette, P. W. (eds.): Paleokarst. Springer, New York, 416 p. in the Castleguard Cave (Alberta, Canada);Harmon, R. S.; Atkinson, T. C. & Atkinson, J. L. (1983): The Mineralogy of Castleguard Cave, Columbia Icefields, Alberta, Canada]. Arctic and Alpine Research, vol. 15, pp. 503–522. in the Grotte de Clamouse, France;Baron, G.; Caillère, S.; Lagrange, R. & Pobeguin, T. (1957): Sur la présence de huntite dans une grotte de l'Hérault (la Clamouse). Comptes Rendus hebdomadaires des séances de l'Académie des Sciences (Paris), vol. 245, pp. 92–94. Fischbeck, R. (1976): Mineralogie und Geochemie carbonatischer Ablagerungen in europäischen Höhlen – ein Beitrag zur Bildung und Diagenese von Speleothemen. Neues Jahrbuch für Mineralogie, Abhandlungen, vol. 126, pp. 269–291. in various caves of the Transvaal Province of South Africa;Martini, J. & Kavalieris, I. (1978): Mineralogy of the Transvaal caves. Transactions of the Geological Society of South Africa, vol. 81, pp. 47–54. in Clearwater Cave, Mulu, Sarawak Laverty, M. (1982): Cave Minerals in the Gunung Mulu National Park, Sarawak. Cave Science 9(2), p. 130 in the Jenolan Caves, Australia;Pogson, R. E.; Osborne, R. E. & Colchester, D. M. (2001): Minerals of the Jenolan Caves – geosphere meets biosphere. Journal and Proceedings of the Royal Society of New South Wales, vol. 134, p. 111. and in the Castañar Cave near Cáceres, Spain.Alonso-Zarza, A. M.; Martín-Pérez, A.; Gil-Peña, I.; Martínez-Flores, E. & Muñoz-Barco, P. (2005): Formacíon de dolomita y huntita en depósitos de moon-milk en la Cueva de Castañar de Ibo (Cáceras). Geogaceta, July 2005, no. 38, pp. 247–250. Alonso-Zarza, A. M. & Martín-Pérez, A. (2008): Dolomite in caves: Recent dolomite formation in oxic, non-sulfate environments, Castañar Cave, Spain. Sedimentary Geology, vol. 205, pp. 160–164.
Syntheses In 1962, huntite was first synthesized by Biedl and Preisinger in experiments conducted at 100 °C and 3.2 bar pressure.Biedl, A. & Preisinger, A. (1962): Synthese von Huntit, Mg3Ca(CO3)4. Anzeiger der mathematisch-naturwissenschaftliche Klasse, Österreichische Akademie der Wissenschaften (Wien), 1962, No.10, pp.148–149.
In 1983, Oomori et al. claimed laboratory synthesis of huntite at 33 °C when adding a sodium carbonate solution to concentrated seawater saturated with calcium bicarbonate.Oomori, T.; Kaneshima, K.; Taira, T. & Kitano, Y. (1983): Synthetic studies of protodolomite from brine waters. Geochemical Journal, vol.17, pp.147–152. In 2006, Zaitseva et al. noted the precipitation of huntite at room temperature and atmospheric pressure. In laboratory experiments originally intended to synthesize magnesium calcite, they had added cultures of Microcoleus chtonoplastes (cyanobacteria) to seawater brine. After 10 months of continuously shaking the samples, they found huntite, magnesite, and aragonite.Zaitseva, L. V.; Orleanskii, V. K.; Gerasimenko, M. & Ushatinskaya, G. T. (2006): The role of cyanobacteria in crystallization of magnesium calcites. Paleontological Journal, vol.40, pp.125–133. In 2012, Hopkinson et al. synthesized the mineral at 52 °C by reacting magnesium calcite with nesquehonite (MgCO3·3H2O).Hopkinson, L.; Kristova, P.; Rutt, K. & Cressey, G. (2012): Phase transitions in the system MgO – CO2 – H2O during CO2 degassing of Mg-bearing solutions. Geochimica et Cosmochimica Acta, vol.76, pp.1–13.
Genesis Huntite, dolomite and magnesite appear to be so very closely related that a genetic relationship seems to be implied.Müller, G.; Irion, G. & Förstner, U. (1972): Formation and diagenesis of inorganic Ca-Mg carbonates in the lacustrine environment. Die Naturwissenschaften, vol.59, pp.158–164. In some instances, all three carbonates are found in close association; for example, Faust (1953) described huntite occurring together with dolomite and magnesite (amongst other minerals); Carpenter (1961)Carpenter, A. B. (1961): Mineral assemblage magnesium calcite – aragonite – huntite at Crestmore, California. Geological Society of America, Abstracts for 1961, p.146. found huntite associated with aragonite, magnesium calcite and dolomite; Larrabee (1969)Larrabee, D. M. (1969) Serpentinite and rodingite in the Hunting Hill Quarry, Montgomery County, Maryland. U.S. Geological Survey Bulletin, no.1283, 34 p. reported on huntite together with (amongst many others) aragonite, calcite, dolomite and magnesite in serpentinite on a weathered dunite rock. A weathered basalt in Australia was found to contain huntite in association with magnesite (Cole & Lancucki, 1975Cole, W. F. & Lancucki, C. J. (1975): Huntite, from Deer Park, Victoria, Australia. American Mineralogist, vol.60, pp.1130–1131. ). Huntite together with magnesite was found by Calvo et al. (1995)Calvo, J. P.; Stamatakis, M. G. & Magganas, A. C. (1955): Clastic huntite in Upper Neogene formations of the Kozani Basin, Macedonia, Northern Greece. Journal of Sedimentary Research, vol.A65, pp.627–632. in lake sediments of Northern Greece. Huntite in combination with magnesite occurs in a weathered serpentinite near Hrubšice, Czech Republic according to Němec (1981)Němec, D. (1981): Huntit ze serpentinitové oblasti u Hrubšic na západni Moravě (Huntite from the serpentinite area at Hrubšice, Western Moravia – English summary). Časopis pro mineralogii a geologii, vol.26, pp.75–78. According to the mineral and locations database of "mindat.org" huntite, together with aragonite, calcite, dolomite and magnesite, can be found in the "U Pustého Mlýna" quarry near Hrubšice, Czech Republic.
Industrial use The most common industrial use of huntite is as a natural mixture with hydromagnesite as a flame retardant or fire retardant additive for polymers. 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 absorbs heat, which helps to cool the burning material, slowing the fire's spread. These mixtures are alternatives to the more commonly used aluminium hydroxide.
Conite