Brushite

Brushite is a phosphate mineral with the chemical formula CaHPO₄·2H₂O. Crystals of the pure compound belong to the monoclinic space group C2/c and are colorless.[1][4] It is the phosphate analogue of the arsenate pharmacolite.

Brushite
Brushite (white) on montmorillonite
General
Category	Phosphate mineral
Formula (repeating unit)	CaHPO4·2H2O
Strunz classification	8.CJ.50
Crystal system	Monoclinic
Space group	Ia (no. 9)
Unit cell	a = 6.265 Å, b = 15.19 Å, c = 5.814 Å; β = 116.47°; Z = 4
Identification
Color	Colorless to pale or ivory-yellow
Crystal habit	Prismatic to tabular acicular crystals; typically powdery or earthy
Cleavage	Perfect on {010} and {001}
Tenacity	Brittle
Mohs scale hardness	2.5
Luster	Vitreous, pearly on cleavages
Diaphaneity	Transparent to translucent
Specific gravity	2.328
Optical properties	Biaxial (+)
Refractive index	nα = 1.539 – 1.540 nβ = 1.544 – 1.546 nγ = 1.551 – 1.552
Birefringence	δ = 0.012
2V angle	Measured: 59 to 87°
Solubility	Readily in HCl
Other characteristics	Piezoelectric
References	[1][2][3][4][5]

Discovery and occurrence

Brushite was first described in 1865 for an occurrence on Aves Island, Nueva Esparta, Venezuela, and named for the American mineralogist George Jarvis Brush (1831–1912).[3] It is believed to be a precursor of apatite and is found in guano-rich caves, formed by the interaction of guano with calcite and clay at a low pH. It occurs in phosphorite deposits and forms encrustations on old bones. It may result from runoff of fields which have received heavy fertilizer applications.[3] Associated minerals include tanarakite, ardealite, hydroxylapatite, variscite and gypsum.[1]

Brushite is the original precipitating material in calcium phosphate kidney stones.[6] It is also one of the minerals present in dental calculi.

References

1. Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2000). "Brushite". Handbook of Mineralogy (PDF). IV (Arsenates, Phosphates, Vanadates). Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209732. Archived from the original (PDF) on 2016-03-04.
2. Brushite. Mineralienatlas]
3. Brushite. Mindat.org
4. Brishite. Webmineral
5. Schofield, P. F.; Knight, K. S.; Houwen, J. A. M. van der; Valsami-Jones, E. (December 2004). "The role of hydrogen bonding in the thermal expansion and dehydration of brushite, di-calcium phosphate dihydrate". Physics and Chemistry of Minerals. 31 (9): 606–624. doi:10.1007/s00269-004-0419-6.
6. "Brushite". Virtual Museum of Molecules and Minerals. Retrieved 22 December 2017.