Gneiss
Rock
About it
Coarse, banded rock with light layers of quartz and feldspar alternating with dark layers of mica or hornblende, formed at high temperature. The Acasta Gneiss of the Northwest Territories, about 4 billion years old, is among the oldest rocks known.
- Type
- Rock (metamorphic)
- Group
- Metamorphic (foliated)
- Specific gravity
- 2.6–3
- Colours
- grey, pink, white, black, banded
- Transparency
- opaque
- Cleavage and fracture
- breaks roughly along the banding
Typical values: real specimens vary. For more, see mindat.org.