Fukalite
| Fukalite | |
|---|---|
 | |
| General | |
| Category | Inosilicates / Silicate-carbonate |
| Formula | Ca 4Si 2O 6(CO3)(OH,F)2 |
| Strunz classification | 9.DQ.05 |
| Dana classification | 78.04.03.01 |
| Crystal system | Orthorhombic |
| Space group | Orthorhombic |
| Unit cell | a = 5.48 Å, b = 3.78 Å, c = 23.42 Å; Z = 2 |
| Identification | |
| Color | White to pale brown |
| Crystal habit | Fine-grained crystalline aggregates |
| Mohs scale hardness | 4 |
| Luster | Vitreous |
| Streak | White |
| Specific gravity | 2.77 |
| Optical properties | Biaxial |
| Refractive index | α = 1.595, β = 1.605, γ = 1.626 |
| 2V angle | ~90° |
| References | [1][2] |
Fukalite is a rare calcium silicate-carbonate mineral with the chemical formula Ca
4Si
2O
6(CO3)(OH,F)2.[1] It was first discovered in 1977 in the Fuka mine located in Okayama Prefecture, Japan, after which the mineral is named.[1]
Discovery and occurrence
[edit]Fukalite was first described by Chiyoko Henmi, Isao Kusachi, Akira Kawahara, and Kitinosuke Henmi in 1977.[1] It occurs as a secondary alteration product of spurrite in high-temperature contact-metamorphic skarn deposits, specifically within spurrite gehlenite skarns.[1]
At its type locality in Fuka, it is found closely associated with calcite and xonotlite.[1] It has also been identified in skarn deposits in Hiroshima Prefecture, Japan, as well as the Gumeshevsk deposit in the Ural Mountains, Russia.[3]
Physical and optical properties
[edit]Fukalite typically forms fine-grained crystalline aggregates, with individual crystals measuring up to 0.2 mm in length.[1] Its color ranges from translucent white to light brown, featuring a vitreous (glassy) luster and a white streak.[2]
It has a Mohs hardness scale rating of 4 (comparable to fluorite) and a measured density of 2.77 g/cm³.[1] Optically, fukalite is biaxial with refractive indices of α = 1.595, β = 1.605, and γ = 1.626, and a 2V angle of approximately 90°.[1]
Crystallography
[edit]Fukalite crystallizes in the orthorhombic crystal system with unit cell dimensions of a = 5.48 Å, b = 3.78 Å, and c = 23.42 Å (Z = 2).[1] Its crystal structure consists of alternating calcium polyhedral layers and silicate-carbonate modules exhibiting structural Order-Disorder (OD) polytypism.
References
[edit]- 1 2 3 4 5 6 7 8 9 10 Henmi, Chiyoko; Kusachi, Isao; Kawahara, Akira; Henmi, Kitinosuke (1977). "Fukalite, a new calcium carbonate silicate hydrate mineral". Mineralogical Journal. 8 (7): 374–380. Bibcode:1977MinJ....8..374H. doi:10.2465/minerj.8.374.
- 1 2 "Fukalite Mineral Data". Webmineral.com. Retrieved 2026-08-15.
- ↑ Merlino, Stefano; Rastsvetaeva, Ramiza K. (2005). "Crystal structure of fukalite dimorph". Doklady Earth Sciences. 405 (9): 1347–1351.
External links
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| Common minerals | ||
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