Kampfite
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| Kampfite | |
|---|---|
-Kampfite_(bluish).jpg) Traskite (brown) and Kampfite (bluish), from Big Creek, Fresno County, California, United States of America | |
| General | |
| Category | Phyllosilicate minerals |
| Formula | Ba12(Si11Al5)O31(CO3)8Cl5 |
| IMA symbol | Kpfb[1] |
| Strunz classification | 9.EG.20 |
| Crystal system | Monoclinic |
| Crystal class | Domatic (m) (same H-M symbol) |
| Space group | Cc |
| Unit cell | a = 31.2329, b = 5.2398 c = 9.0966 [Å]; β = 106.933°; Z = 1 |
| Identification | |
| Color | Light blue gray |
| Crystal habit | Irregular grains or anhedral crystal inclusions |
| Cleavage | Good on {001} |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 3 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 3.45 |
| Optical properties | Uniaxial – (strongly pseudohexagonal) |
| Refractive index | nω = 1.642 nε = 1.594 |
| Birefringence | δ = 0.048 |
| References | [2][3] |
Kampfite is a rare barium silicate–carbonate–halide mineral with the chemical formula Ba12(Si11Al5)O31(CO3)8Cl5. Discovered in 1964 and described in 2001, it is named after Anthony R. Kampf. The mineral is known only from Fresno County, California.
Kampfite is translucent and light blue-gray in color. Specimens occur as irregular masses up to 1 cm (0.39 in) in size.[4]
Composition and structure
When first described, the formula was identified as Ba6[(Si,Al)O2]8(CO3)2Cl2(Cl,H2O)2.[5] Subsequent work on analyzing the crystal structure led to a revised formula of Ba12(Si11Al5)O31(CO3)8Cl5. The structural H2O noted in the original description was not found in the later work.[6]
The structure consists of double layers of tetrahedra connected by barium-containing polyhedra. It is this layering which causes kampfite's one perfect cleavage.[7][8] Kampfite shares chemical and structural similarities with cymrite.[7] As of 2007[update], it is the only known barium silicate carbonate aside from fencooperite.[6]
Occurrence
Kampfite has been found in association with celsian, fresnoite, macdonaldite, pyrrhotite, titantaramellite, traskite, and witherite.[4] The mineral is known only from locations in Fresno County, California.[2][4] Kampfite is found in quartz-rich regions of sanbornite rocks[5] within gneiss which has undergone contact metamorphism associated with an adjacent granodiorite intrusive.[4]