Min. [ad. Ger. tridymit (vom Rath, 1866), f. Gr. τρίδυμος threefold, f. τρι-, TRI- + -δυμ-ος, as in δίδυμος twin; named in allusion to its compound forms consisting of three individual crystals.] A crystallized form of silica, occurring in small hexagonal tables, found in trachyte and other igneous rocks.
1868. Dana, Min. (ed. 5), 805. Tridymite occurs in small hexagonal tables, colorless and transparent, which are usually compound, and mostly of three individuals.
1888. Rutley, Rock-Forming Min., 130. Tridymite is essentially a volcanic mineral.
