Chemical formula Na2Mg3Al2Si8O22(OH)2
Class Inosilicate
Double chains of linked tetrahedra
Crystal system Monoclinic
Habit Acicular
Color Blue
Hardness 6-6.5
Specific gravity 3.1 to 3.2
Cleavage/fracture Two perfect prismatic {110}/
Luster Vitreous
Transparency Transparent to translucent
Streak White to very light blue
δ 0.01 – 0.02
PPL Colorless to blue or violet
Often strongly pleochroic
XPL Up to 2nd order interference colors
Interference color may be masked by mineral color
after Perkins, 333

Glaucophane in Hand Sample

Glaucophane in Turkish blueschist
Glaucophane in Greek blueschist (the two samples on the left)
Fine-grained blueschist
Medium-grained blueschist
Garnet-studded retrograde blueschist after eclogite

Glaucophane in Thin Section

Glaucophane in blueschist, plane polars

Glaucophane in blueschist, crossed polars

Further Reading

Glaucophane at
Glaucophane at