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Chapmanite

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Chapmanite
Yellow-green earthy massive chapmanite
General
CategoryPhyllosilicate
Formula
(repeating unit)
Fe2Sb(SiO4)2(OH)
Strunz classification9.ED.25
Crystal systemMonoclinic
Crystal classDomatic (m)
(same H-M symbol)
Space groupCm
Identification
ColorYellow, green, olive green
Crystal habitEarthy massive; granular
CleavagePoor
FractureConchoidal to irregular
Mohs scale hardness2.5
LusterNonmetallic, dull to adamantine
StreakYellowish green
Specific gravity3.69-3.75
Refractive indexnα=1.850 nβ=1.950 nγ=1.960
PleochroismNone

Chapmanite is a rare silicate mineral belonging to the nesosilicate group, discovered in 1924, and named in honour of the late Edward John Chapman (1821–1904), a geology professor at the University of Toronto. Chemically, it is an iron antimony silicate, closely related to bismutoferrite, and may contain aluminium impurities. It is closely associated with silver mines, most notably the Keeley mine in Ontario, Canada, found in quartz veinlets containing graphite in gneiss. It takes the form of a powdery, yellow-green, semitransparent solid, and leaves a streak of the same color. Early German texts have referred to the mineral as antimon-hypochlorite.

It was recently rediscovered in the southern hemisphere at the abandoned Argent lead mine in Bushveld series rocks of South Africa.

References