Johnbaumite

Johnbaumite
General
Category	Apatite group
Formula	Ca5(AsO4)3OH
IMA symbol	Jbm
Strunz classification	08.BN.05
Dana classification	41.08.03.03
Crystal system	Hexagonal
Crystal class	Dipyramidal (8/m)
Space group	P63/m
Identification
Colour	Greyish white to colourless
Crystal habit	Anhedral grains, granular minerals without the expression of crystal shapes and massive, uniformly indistinguishable crystals forming large masses.
Cleavage	Distinct {1010}
Fracture	Irregular/Uneven
Tenacity	Brittle
Mohs scale hardness	≈ 4.5
Luster	Adamantine to greasy on fracture surfaces, vitreous on cleavage surfaces
Streak	White
Diaphaneity	Transparent
Density	3.65 – 3.73 g/cm3
Optical properties	Uniaxial (−)
Refractive index	nω = 1.687 nε = 1.684
Birefringence	0.003
Pleochroism	Non-pleochroic
Extinction	Parallel
References

Johnbaumite is a calcium arsenate hydroxide mineral. It was first described in 1980, where it appeared in Franklin, Sussex County, New Jersey. Johnbaumite was discovered at Harstigen mine in Sweden in the 19th century, but it was described as svabite.

Etymology

It is named after geologist John Leach Baum (March 15, 1916 – October 16, 2011), who found the original specimen in 1944. He was a significant contributor to the geology and mineralogy of the Franklin deposit, and the Curator Emeritus at the Franklin Mineral Museum.

See also

• Hydroxyapatite
• Svabite

References

Further reading

• Biagioni C, Bosi F, Hålenius U, Pasero M (2017) The crystal structure of turneaureite, Ca5(AsO4)3Cl, the arsenate analog of chlorapatite, and its relationships with the arsenate apatites johnbaumite and svabite, American Mineralogist, 102, 1981–1986
• Lee Y J, Stephens P W, Tang Y, Li W, Phillips B L, Parise J B, Reeder R J (2009) Arsenate substitution in hydroxylapatite: Structural characterization of the Ca5(PxAs1-xO4)3OH solid solution, American Mineralogist, 94, 666–675
• Zheng Y, Gao T, Gong Y, Ma S, Yang M, Chen P (2015) Electronic, vibrational and thermodynamic properties of Ca10(AsO4)6(OH)2: first principles study, The European Physical Journal of Applied Physics, 72, 1–7
• Anthony J W, Bideaux R A, Bladh K W, and Nichols M C (1990) Handbook of Mineralogy, Mineral Data Publishing, Tucson Arizona, USA, by permission of the Mineralogical Society of America.