from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A rare mineral of volcanic rocks that solidified at a high temperature, with the chemical composition silicon dioxide, SiO2. Tridymite is chemically identical to quartz, but has a different crystal structure. Sometimes contains sodium aluminum silicate, which seems to be expelled when quartz solidifies at lower temperatures.
from the GNU version of the Collaborative International Dictionary of English
- n. Pure silica, like quartz, but crystallizing in hexagonal tables. It is found in trachyte and similar rocks.
from The Century Dictionary and Cyclopedia
- n. A crystallized form of silica, found in minute transparent tabular hexagonal crystals in trachyte and other igneous rocks, usually in twinned groups, and commonly of three crystals. It has a lower specific gravity than quartz (2.2), and is soluble in boiling sodium carbonate.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a mineral form of silica
The name refers to the peculiar habit of crystallizing in groups of three individuals. (Wiktionary)