Its name comes, according to Pliny, from Obsidius who brought it from Ethiopia, which would have led the Romans to call it “obsidius lapis”.
From the seventeenth century we find the names of hyalopsite, mountain mahogany, Iceland black agate, mirror of the Incas, gallinaceous stone …
It was first classified among the rocks and among the “hard stones” by Brongniart.
Haüy, who acknowledged his origin, called it “glassy lava obsidian”.
Overall, this is a volcanic glass, composed of tectosilicates, which is formed by rapid cooling of a magma in which the dispersed atoms in the melt, did not have the time to order in the crystal system: it is the vitrified form of rhyolite.
We find several varieties:
snowflakes obsidian, like snowflakes, in flowers, whose interior is dotted with gray spots, which comes mainly from Mexico and the United States,
gold or silver obsidian, which has stains of that color,
the celestial eye obsidian with iridescent concentric purple-gray or pale green zones,
the apache tears, which are only small “drops” of volcanic glass 1 to 2 mm in diameter and 3 to 5 cm long.
Some books indicate a “flowering obsidian” which comes from Oregon, rust-colored or bronze spotted with black or silver, more or less iridescent .
The rainbow obsidians having all the colors of the rainbow, due to the needles of hedenbergite and come from Mexico.