Aheylite
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| Aheylite | |
|---|---|
 Size: 3.5 × 2.3 × 0.8 cm. Translucent ~0.2 cm spheres of aheylite are perched on dark cassiterite, together with elongated quartz crystals. | |
| General | |
| Category | Phosphate minerals |
| Formula | (Fe2+,Zn)Al6(OH)8(PO4)4·4(H2O) |
| IMA symbol | Ahe[1] |
| Strunz classification | 8.DD.15 |
| Crystal system | Triclinic Unknown space group |
| Unit cell | a = 7.885, b = 10.199 c = 7.672 [Å]; α = 110.84° β = 115.12°, γ = 67.51°; Z = 1 |
| Identification | |
| Color | Very pale blue, pale green, to blue-green |
| Crystal habit | Interlocked crystals in felted and matted aggregates forming botryoidal, spherulitic masses; radiating, prismatic groups |
| Cleavage | Perfect {001}, {010} good |
| Fracture | Hackly to splintery |
| Tenacity | Brittle |
| Mohs scale hardness | 5 to 5.5 |
| Luster | Porcelaneous to subvitreous |
| Streak | White to greenish white |
| Diaphaneity | Transparent in thin flakes |
| Specific gravity | 2.84 |
| Optical properties | Biaxial (+) |
| Refractive index | ~1.63 |
| References | [2][3][4] |
Aheylite is a rare phosphate mineral with formula (Fe2+Zn)Al6[(OH)4|(PO4)2]2·4(H2O). It occurs as pale blue to pale green triclinic crystal masses.[2] Aheylite was made the newest member of the turquoise group in 1984 by International Mineralogical Association Commission on New Minerals and Mineral Names.
The turquoise group has a basic formula of A0–1B6(PO4)4−x(PO3OH)x(OH)8·4H2O. This group contains five other minerals. In addition to aheylite: planerite, turquoise, faustite, chalcosiderite, and an unnamed Fe2+-Fe3+ analogue. Aheylite is distinguished in this group by having Fe2+ dominant in the A-site. The ideal aheylite has a formula of Fe2+Al6(PO4)4(OH)8·4H2O. Its color is pale blue or green. With turquoise family the blue color is said to come from the octahedral coordination of Cu2+ in the absence of Fe3+.[5]
Name and discovery
It was first described for an occurrence in the Huanuni mine, Huanuni, Oruro Department, Bolivia, and named for Allen V. Heyl (1918–2008), an economic geologist for the United States Geological Survey.[3] It was eventually described by Eugene Foord and Joseph Taggart in 1998.[5]