Johnbaumite
General
Category	Apatite group
Formula	Ca5(AsO4)3OH
IMA symbol	Jbm[1]
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	[2][3]

Johnbaumite is a calcium arsenate hydroxide mineral. It was first described in 1980, where it appeared in Franklin, Sussex County, New Jersey.^[4] Johnbaumite was discovered at Harstigen mine in Sweden in the 19th century, but it was described as svabite.^[5]

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.

• Hydroxyapatite
• Svabite

• 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.