CHIASTOLITE

Hollow-spar. A mineral found imbedded in clay-slate: it occurs in the slate of Cumber land, and of Antrim in Ireland: in rhomboidal prisms, exteriorly greyish-white, and interiorly black. Some of the sections of the crystals have the form of an X, hence the term from;c'«l'»'i to mark with that letter. [s. 1374]