Mineral description : Cordierite

Cordierite from Evje, Norway. Cordierite from Stakholmen.

Mineral class Silicates : Cyclosilicate : Andalusite - Sillimanite - Kyanite group.

Chemical formula Mg₂Al₄Si₅O₁₈

Crystal system Orthorombic.

Habitus Short prismatic crystals, commonly twinned, or massive grainy aggregates.

Cleavage Distinct, fracture conchoidal.

Hardness 7-7.5

Density 2.60-2.66

Color Usually gray, but nuances in brown and blue is also common. Often strongly pleochroic. Transparent to translucent.

Streak Colorless.

Luster Vitreous.

Description

Occurance Formed in igneous and contact metamorphic rocks (for example gneiss).

Associates

Notes Easily mistaken for quartz. Distinguished from quartz by heating in a flame. Cordierite is much easier made to glow than quartz.
Fusible on thin edges in a flame.

Locations A very common mineral in Sweden. It's a component in manySwedish schists, especially in central Sweden.

Falu mine. Up to dm sized yellowish brown to gray concretions in chlorite schist.
Riddarhyttan (esp. Källfallsgruvan). As yellowish brown concretions in schist.
Mellanfjärden, Hälsingland. As big clear crystals in quartzite bedrock.
Hudiksvall. As a black iron rich variety.
Nyköping area. Beautiful bllue concretions.

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Last changed : 1998-03-07

Mineral class	Silicates : Cyclosilicate : Andalusite - Sillimanite - Kyanite group.
Chemical formula	Mg₂Al₄Si₅O₁₈
Crystal system	Orthorombic.
Habitus	Short prismatic crystals, commonly twinned, or massive grainy aggregates.
Cleavage	Distinct, fracture conchoidal.
Hardness	7-7.5
Density	2.60-2.66
Color	Usually gray, but nuances in brown and blue is also common. Often strongly pleochroic. Transparent to translucent.
Streak	Colorless.
Luster	Vitreous.
Description
Occurance	Formed in igneous and contact metamorphic rocks (for example gneiss).
Associates
Notes	Easily mistaken for quartz. Distinguished from quartz by heating in a flame. Cordierite is much easier made to glow than quartz. Fusible on thin edges in a flame.
Locations	A very common mineral in Sweden. It's a component in manySwedish schists, especially in central Sweden. Falu mine. Up to dm sized yellowish brown to gray concretions in chlorite schist. Riddarhyttan (esp. Källfallsgruvan). As yellowish brown concretions in schist. Mellanfjärden, Hälsingland. As big clear crystals in quartzite bedrock. Hudiksvall. As a black iron rich variety. Nyköping area. Beautiful bllue concretions.