Tachylite

Tachylit ( gr = ταχύς quickly and λίθος = stone ) is a black -green to black volcanic glass with basaltic chemistry. It was first described by A. Breithaupt in 1826. Tachylite caused by the rapid cooling of basaltic lavas, for example, by contact with seawater, creating a formation of crystals is prevented. Like all volcanic glasses are Tachylite unstable; over long geological periods they absorb water and are thus palagonitisiert.