Hydrogrossular
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Hydrogrossular is a calcium aluminium garnet series. The endmembers of the hydrogarnet family depend on the degree of substitution:
grossular: x = 0
hibschite: 0.2 < x < 1.5
katoite: 1.5 < x < 3.
Hydrogrossular is a garnet variety in which a Si⁴⁺... Wikipedia
Crystal habit: Massive
Crystal system: Cubic
Formula (repeating unit): Ca3Al2(SiO4)3−x(OH)4x
Mohs scale hardness: 7–7.5
Optical properties: single refractive, anomalous aggregate reaction
Refractive index: 1.810+0.004; −0.020
Specific gravity: 4.15+0.05; −0.03