Huntite is a carbonate mineral with the chemical formula Mg₃Ca(CO₃)₄. It crystallizes in the trigonal system and typically occurs as platy crystals and powdery masses.
Discovery and Naming
Huntite was formally announced as a new mineral in 1953 by George Faust, who named it in honor of his former teacher, Walter Frederick Hunt (1882–1975), Professor of Petrology at the University of Michigan. Faust acknowledged that the mineral had likely been discovered earlier but had been misidentified as impure magnesite by W. E. Ford in 1917.
Properties
| Property | Description |
|---|---|
| Category | Carbonate mineral |
| Chemical formula | Mg₃Ca(CO₃)₄ |
| Crystal system | Trigonal |
| Crystal class | Trapezohedral (32) |
| Space group | R32 |
| Color | White, lemon white |
| Crystal habit | Platy crystals; compact chalklike masses |
| Mohs hardness | 1–2 |
| Luster | Earthy (dull) |
| Streak | White |
| Specific gravity | 2.696 |
| Refractive index | nω = 1.622, nε = 1.615 |
Occurrence
Huntite is found in a variety of environments, including modern carbonate sediments of tidal flats (e.g., Persian Gulf), seasonal salt lakes (Turkey), playa lakes (British Columbia, Canada), lacustrine deposits (Greece), and sabkha sediments (Tunisia). It is also commonly found in caves, including Carlsbad Caverns National Park (New Mexico, USA), Castleguard Cave (Alberta, Canada), Grotte de Clamouse (France), Jenolan Caves (Australia), and Castañar Cave (Spain).
It often occurs in association with other magnesium/calcium carbonates such as dolomite, magnesite, and hydromagnesite. Large commercial deposits exist in Turkey and Greece.
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. When heated, huntite decomposes endothermically over a temperature range of approximately 450–800 °C, releasing carbon dioxide, which helps cool the burning material and slow the spread of fire. These mixtures serve as alternatives to the more commonly used aluminium hydroxide.
Historical Use as a Pigment
For most of recorded history, huntite's main use was as a white pigment. It has been identified in ancient rock art and Egyptian tomb paintings.
Synthesis
Huntite was first synthesized in 1962 by Biedl and Preisinger at 100 °C and 3.2 bar CO₂ pressure. Subsequent laboratory syntheses have been achieved at lower temperatures, including at 33 °C (Oomori et al., 1983) and even at room temperature and atmospheric pressure with the aid of cyanobacteria cultures (Zaitseva et al., 2006).
Conite
A mineral with the same composition as huntite was known for over 200 years under the name conite (German: Konit), first described by Retzius in 1798. However, because the original type locality for conite was never established, historical priority over the name "huntite" cannot be claimed.
