Plagioclase
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Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the... Wikipedia
Hardness: 6 to 6.5
Category: Feldspar mineral group, tectosilicate
Color: White, gray, or bluish white
Crystal class: Pinacoidal (1); (same H-M symbol)
Crystal system: Triclinic
Diaphaneity: Transparent to translucent
Formula (repeating unit): NaAlSi3O8 – CaAl2Si2O8