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Formula: Ca(PO3OH).2H2O
Hydrated acid phosphate
Crystal System: Monoclinic
Specific gravity: 2.30 to 2.33 measured, 2.32 calculated
Hardness: 2½
Streak: White
Colour: Colourless, light yellow; colourless in transmitted light
Solubility: Readily soluble in hydrochloric acid
Environments
Brushite is one of the most common cave minerals, in guano deposits, and in
phosphorite, formed at low pH (acid) by reaction of phosphate-rich solutions with
calcite and clay (HOM). It also occurs as
incrustations on ancient bones and crypts. It may form due to run-off from heavily fertilized fields (Mindat). Associated minerals
include taranakite, ardealite,
hydroxylapatite, variscite and
gypsum
(HOM).
Brushite loses all water by 100oC forming monetite
(Dana).
Localities
In the Apulian caves, southern Italy, brushite is associated with hydroxylapatite
and taranakite. The minerals were probably formed by interaction between phosphatic solutions
derived from bat guano and calcite and clay minerals
from the substratum. However, the data also suggest precipitation from solution for brushite and
hydroxylapatite
(AM 76.1722-1727).
The type locality is Aves Island, Nueva Esparta, Venezuela, where brushite has been found in a cave guano deposit, in druses in
phosphate rock. Brushite is rather widespread in very small amoiunts in phosphate rock deposits. It typically occurs as drusy
crystals in crevices in massive apatite and is a late-formed, low-temperature product.
Monetite forms at higher temperatures. Brushite has been observed altered to
carbonate-hydroxylapatite and to whitlockite
(AM 28.218, Mindat).
At Pig Hole Cave, Giles county, Virginia, USA, brushite occurs as nodular masses of platy crystals in the lower part of a bat
guano and hair deposit. The temperature of the air within the cave has been found to range from 8oC to 10oC.
The cave is inhabited by a few bats and possibly small mammals or maybe owls. The cave is in a
cherty limestone. A few
quartz crystals are found in some passageways, and cobbles and boulders of
sandstone and quartzite plus silt and
clay also occur within the cave. Clusters of transparent
selenite crystals occur in the clay in a few places.
The material of the bottom layer of the deposit, about a foot deep, is distinctly different from that above, and it is here that the
brushite occurs. The layer contains masses of black carbonaceous material, brushite and
taranakite. The brushite occurs as nodular masses of minute crystals sporadically
throughout this lower zone.
(AM 41:616).
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