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Earth lab datasite

Tourmaline
Silicate schorl in granite
silicate
Na (Fe Mn)3 Al6 B3 Si6 O27 OH3 F?
Scale bar = 1 centimetre
cleavage: Very indistinct
crystal system: Trigonal
hardness 7.0 - 7.5
relative density 3.0 - 3.2
Bovey Tracey, Devon
25 K 5