Cuspidine

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Cuspidine
General
CategorySorosilicate
Formula
(repeating unit)
Ca4(Si2O7)(F,OH)2
Strunz classification9.BE.17
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Unit cella = 10.93 Å, b = 10.57 Å,
c = 7.57 Å; β = 110.11°; Z=4
Identification
ColorColorless, tan, light brown, pale red
Crystal habitMinute spearhead-shaped crystals, acicular, granular
TwinningSimple, lamellar, polysynthetic on {100}
CleavageGood on {001} imperfect on {110}
FractureUneven
TenacityBrittle
Mohs scale hardness5-6
LusterVitreous
DiaphaneityTransparent to translucent
Specific gravity2.85-2.96
Optical propertiesBiaxial (+)
Refractive indexnα = 1.586 - 1.594 nβ = 1.589 - 1.596 nγ = 1.598 - 1.606
Birefringenceδ = 0.012
2V angleMeasured: 59° to 71°
References[1][2][3]

Cuspidine is a fluorine bearing calcium silicate mineral (sorosilicate) with formula: Ca4(Si2O7)(F,OH)2.[1] Cuspidine crystallizes in the monoclinic crystal system and occurs as acicular to spear shaped pale red to light brown crystals. It is a member of the wöhlerite group.

Cuspidine was first described in 1876 for an occurrence in Monte Somma, Italy.[1][3] The name is from the Greek cuspis for spear from its characteristic crystal form.[1] Cuspidine occurs as crystals in tuff from Monte Somma. In the Franklin, New Jersey mine area it occurs in contact metamorphosed limestone. In Dupezeh Mountain, Iraq, it occurs in melilite bearing skarn. Associated minerals include augite, hornblende, diopside, grossular, biotite, phlogopite, monticellite, wollastonite, calcite, spinel, magnetite and perovskite.[3]

References[edit]