Johnbaumite

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

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]

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