Image: <bdi><a href="https://www.wikidata.org/wiki/Q56247090" class="extiw" title="d:Q56247090"><span title="mineral collector and dealer">Robert M. Lavinsky</span></a></bdi> (CC BY-SA 3.0)

orthorhombiccommonSilicates

Andalusite

Al2SiO5

This specimen is a chiastolite variety of andalusite, characterized by its brownish-grey color and a distinctive black cross pattern formed by carbonaceous inclusions within the prismatic crystal.

Andalusite Physical Properties

Mohs Hardness

6.5

Crystal System

orthorhombic

Luster

vitreous

Streak Color

white

Cleavage

good on {110}

Fracture

uneven

Specific Gravity

3.15

Colors

white, gray, pink, red, brown, yellow, green, black

Transparency

transparent to opaque

Type Locality

Tyrol, Austria

Mineral Group

Silicates

Uses

refractory material, gemstone, collector

Associated Minerals

quartz, muscovite, biotite, cordierite, kyanite, sillimanite, staurolite, garnet

Rarity

common

Geological Context

Andalusite is a common metamorphic mineral, typically forming in medium-grade regional metamorphism of pelitic rocks (shales and mudstones). It is one of three polymorphs of Al₂SiO₅, stable at lower temperatures and pressures.

Back to Collection

Related Specimens

Peridot

Tremolite

Glaucophane

Tiger's Eye

Jasper

Unakite