Cordierite
Mg2AI3(ALSi5O18)
Chemical name
Cordierite
Mineral name
Cordierite
Chemical formula
Mg2AI3(ALSi5O18)
Crystal system
orthorhombic
Crystal Class
Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space Group
Cccm
Unit cell
a [Å]:17079
b [Å]:9730
c [Å]:9356
Formula units
Z = 4
Twinning
Common on {110}, {130}, simple, lamellar, cyclical
Mohs hardness
7 - 7,5
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
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