Figure 1. A specimen of andalusite from Tyrol, Austria.
Figure 2. Chiastolite.
Andalusite is usually pink but white, gray, yellow, green, and violet varieties also occur frequently. It crystallizes in the orthorhombic system. Hardness: 7.5.
Chiastolite is a variety of andalusite, aluminium silicate (Al2OSiO4), found in metamorphic rocks (Figure 2). It has elongated prismatic crystals, which in cross-section show a black cross on a gray ground. Hardness 7.5; relative density 3.1–3.2.