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Hodgkinsonite from Franklin Mine, Franklin, New Jersey USA. The translucent and lustrous crystals reach 8 mm and the main crystal here is doubly terminated.
Category Nesosilicate
(repeating unit)
Strunz classification 9.AE.20
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/a
Unit cell a = 11.76, b = 5.31
c = 8.18 [Å]; β = 95.42°, Z = 4
Mohs scale hardness4 12 - 5
Optical properties Biaxial (-)
Refractive index nα = 1.720 nβ = 1.741 nγ = 1.746
Birefringence δ = 0.026
Dispersion r < v moderate

Hodgkinsonite is a rare zinc manganese silicate mineral Zn2MnSiO4(OH)2. It crystallizes in the monoclinic system and typically forms radiating to acicular prismatic crystals with variable color from pink, yellow-red to deep red. Hodgkinsonite was discovered in 1913 by H. H. Hodgkinson, for whom it is named in Franklin, New Jersey, and it is only found in that area.[1]


  1. ^ Mineral Galleries. Accessed August 22, 2008.

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