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Formula: CaAl3(PO4)(PO3OH)(OH)6
Hydrated phosphate containing hydroxyl, plumbogummite group,
alunite supergroup
Crystal System: Trigonal
Specific gravity: 2.78 to 3.04 measured, 3.00 calculated
Hardness: 5
Streak: White
Colour: Yellow, white, grey; colourless in transmitted light.
Solubility: Soluble with difficulty in acids.
Common impurities: Sr and Ba substituting for Ca and Fe3+ for Al (Dana).
Environments:
Pegmatites
Sedimentary environments
Hydrothermal environments
Crandallite is a secondary mineral that occurs in iron-rich, silica-poor
phosphate deposits and
as an alteration product in pegmatites
(Dana). It may be found as a pseudomorph after
gordonite
(Dana).
Localities
In the phosphate deposits of South Australia crandallite is found as a replacement of other phosphate
minerals, notably wavellite, also
apatite,
fluellite and minyulite
(AJM 17.1.14).
Crandallite from South Australia - Image
At the Milgun Variscite Mine, Milgun Station, Meekatharra Shire, Western Australia,
crandallite is a common alteration product of variscite; it
crystallised late in the paragenetic sequence, and occurs as inclusions in
hydroxylapatite. The
variscite deposits are hosted by marine sedimentary rocks
(AJM 20.2.24).
At the Central Florida Phosphate Mining District, Polk county, Florida, USA, crandallite is associated with
clay, millisite
and wavellite (Dana).
Crandallite from the Central Florida Phosphate
Mining District - Image
At the type locality, the Brooklyn Mine, Silver City, Tintic Mining District, Juab County, Utah, USA,
crandallite occurs in a matrix of quartz -
baryte where it fills cavities, either fully or partially. The cavities
range in size from a few millimeters to 6 cm in diameter. The vein material also contains
pyrite, enargite,
galena and sphalerite.
Tenorite crusts up to half a millimeter thick covered the
crandallite in a few specimens.
Crandallite is white to pale grey, sometimes with shades of yellow and brown. So far (published March-April
2024), crandallite in the Tintic district has been seen only from the Brooklyn mine, although closely related
minerals such as arsenocrandallite,
arsenogoyazite and
svanbergite have been found at other mines, so it is quite likely that
crandallite may occur at these other mines as well
(MinRec 55.2.197-198).
At Fairfield, Sunshine Mining District, Utah County, Utah, USA, crandallite is associated with
millisite,
wardite,
variscite,
gordonite,
englishite,
montgomeryite,
overite,
kolbeckite and
apatite
(Dana).
Crandallite from Fairfield - Image
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