Cordierite

Cordierite

Mg2AI3(ALSi5O18)

Crystal system

orthorhombic

Crystal Class

Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)

Space Group

Cccm

Unit cell

Formula units

Z = 4

Twinning

Common on {110}, {130}, simple, lamellar, cyclical

Mohs hardness

7 - 7,5

Density [g/cm3]

2.6 - 2.66

Cleavage

Fair on {100}, poor on {001} and {010}

Fracture / Tenacity

Subconchoidal, brittle

Color

Blue, smoky blue, bluish violet; greenish, yellowish brown, gray; colorless to very pale blue in thin section in transmitted light

Streak

White

Transparency

Transparent to translucent

Luster

Greasy or vitreous

Refractive Index

nα = 1.527 - 1.560 nβ = 1.532 - 1.574 nΥ = 1.538 - 1.578 Indices increase with Fe content.

Pleochroism δ

X = pale yellow, green; Y = violet, blue-violet; Z = pale blue