Alleghanyite is a moderately rare humite mineral with formula Mn5(SiO4)2(OH)2, belonging to the nesosilicates class. In general its occurrences are related with metamorphic (metamorphosed) manganese deposits. The mineral is named after Alleghany County, North Carolina, US.[2]

Alleghanyite
Alleghanyite crystals up to 2 mm in size in a mixed franklinite/calcite/willemite block of 11×6.5×4 cm size. Location: Sterling Mine, Sussex County, New Jersey, US.
General
CategoryNesosilicates
Humite group
Formula
(repeating unit)
Mn5(SiO4)2(OH)2
IMA symbolAlh[1]
Strunz classification9.AF.45
Dana classification52.3.2b.1
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/a
Unit cella = 10.46, b = 4.86
c = 8.3 [Å]; β = 109.133°; Z = 2
Identification
Formula mass492.87 g/mol
ColorBrown, bright pink, grayish pink, white
Crystal habitGranular; anhedral to subhedral crystals in matrix
CleavageNone
FractureConchoidal
TenacityBrittle
Mohs scale hardness5–6
LusterVitreous
DiaphaneityTransparent to translucent
Specific gravity4 (meas.), 4.11 (calc.)
Optical propertiesBiaxial (−)
Refractive indexnα = 1.756
nβ = 1.78
nγ = 1.792
Birefringence0.036
2V angle72° (meas.), 68° (calc.)
Other characteristicsNon-fluorescent
References[2][3]

See also

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References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Alleghanyite. Mindat
  3. ^ Alleghanyite. Webmineral