from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A yellowish to black mineral, Fe2SiO4, of the olivine group.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Yellow, olive green, brown or black mineral with orthorhombic crystals of the olivine group, Fe2SiO4.
from the GNU version of the Collaborative International Dictionary of English
- n. A black, greenish, or brownish mineral of the chrysolite group. It is a silicate of iron.
from The Century Dictionary and Cyclopedia
- n. A black, greenish, or brownish, sometimes iridescent, mineral, consisting mainly of silicate of iron and belonging to the chrysolite group.
All of the brightly colored crystals are of the same mineral (an iron silicate called fayalite) but display different colors because the lattices of each crystal are at different angles to the plane of the section.
The black network within the fayalite crystals is of a second mineral, an iron-aluminum spinel called hercynite, that crystallized at the same time as the fayalite, giving rise to complex intergrowths of the two minerals.