Jump to content

Aheylite

From Wikipedia, the free encyclopedia
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
CategoryPhosphate minerals
Formula
(repeating unit)
(Fe2+,Zn)Al6(OH)8(PO4)4·4(H2O)
IMA symbolAhe[1]
Strunz classification8.DD.15
Crystal systemTriclinic
Unknown space group
Unit cella = 7.885, b = 10.199
c = 7.672 [Å]; α = 110.84°
β = 115.12°, γ = 67.51°; Z = 1
Identification
ColorVery pale blue, pale green, to blue-green
Crystal habitInterlocked crystals in felted and matted aggregates forming botryoidal, spherulitic masses; radiating, prismatic groups
CleavagePerfect {001}, {010} good
FractureHackly to splintery
TenacityBrittle
Mohs scale hardness5 to 5.5
LusterPorcelaneous to subvitreous
StreakWhite to greenish white
DiaphaneityTransparent in thin flakes
Specific gravity2.84
Optical propertiesBiaxial (+)
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.

Composition

[edit]

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

[edit]

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 discovered by Eugene Foord and Joseph Taggart.[5]

Occurrence

[edit]

In addition to the type locality in Bolivia it has been reported from the Bali Lo prospect in the Capricorn Range, Western Australia[2] and the Les Montmins Mine, Auvergne, France.[3] It is a turquoise group mineral and occurs as a late hydrothermal phase in a tin deposit associated with variscite, vivianite, wavellite, cassiterite, sphalerite, pyrite and quartz in the type locality.[2][4]

Physical properties

[edit]

It is found as an isolated mass of hemispheres and spheres clumped together. It has a vitreous to dull luster. It has a hackly to splintery fracture and it has a brittle tenacity. The hardness is about 5–5.5, and the specific gravity is 2.84. As far as optical properties, it had thin flakes; ipale blue, green to blue-green color; it streaks white, and has a subvitreous luster.[5]

References

[edit]
  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d Aheylite. Handbook of Mineralogy
  3. ^ a b c Aheylite. Mindat.org
  4. ^ a b Aheylite. Webmineral
  5. ^ a b c Eugene E. Foord and Joseph E. Taggart, Jr., A reexamination of the turquoise group: the mineral aheylite, plane rite (redefined), turquoise and coeruleolactite, Mineralogical Magazine, February 1998, Vol. 62(1), pp. 93–111