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Formula: ☐(NaCa)(Mg4Al)Si8O22(OH)2
Inosilicate (chain silicate), winchite group, amphibole mineral
Specific gravity: 2.97 to 3.175 measured, 3/02 calculated
Hardness: 5 to 6
Streak: Pale blue-grey
Colour: Cobalt-blue to violet-blue, lavender-grey, grey, colourless
Common impurities: Ti,Mn,Na,K
Environments
Winchite occurs in schists with low-grade metamorphosed
manganese deposits; in metamorphically-altered
basalts of the
blueschist facies and
amphibolite-eclogite
facies; and in manganiferous cherts that have undergone
blueschist facies metamorphism
(HOM).
Localities
The type locality was stated as the Kajlidongri mine, Madhya Pradesh, India, but an extensive search for winchite
by microprobe anlyses of violet amphiboles obtained from there failed to
identify any sodic calcic amphiboles and none is near to the end-member
composition of winchite. It is suggested, but not conclusively proved, that the original analysis of
winchite was in error
(AM 66.625-631).
At Ward Creek [1], Cazadero, Coast Range, Sonoma county, California, USA, winchite is associated with
actinolite, glaucophane,
albite and quartz
(HOM).
At El Valle del Espiritu Santo, Margarita Island, Nueva Esparta, Venezuela, winchite is associated with
omphacite, garnet,
rutile, quartz,
actinolite, epidote,
albite, titanite and
apatite
(HOM).
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