Chiastolite
Variety Al2SiO5
Also called Cross stone
About it
Andalusite crystals with dark carbon inclusions that form a cross or X when cut across. Found in slate and schist; Lancaster, Massachusetts, and Bimbowrie, South Australia, are classic, and China supplies polished slices.
- Type
- Variety
- Group
- Andalusite variety
- Formula
- Al2SiO5
- Hardness (Mohs)
- 6.5–7.5
- Specific gravity
- 3.1–3.2
- Streak
- white
- Lustre
- vitreous (glassy), dull
- Crystal system
- Orthorhombic
- Colours
- grey, brown, pinkish brown, with a dark cross
- Transparency
- opaque
- Cleavage and fracture
- good prismatic; uneven fracture
Typical values: real specimens vary. For more, see mindat.org.