thaumasite

from The Century Dictionary.

• noun A mineral occurring in massive forms of a dull-white color, consisting of the silicate, carbonate, and sulphate of calcium with water. The name has reference to its unusual composition.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mineralogy A hexagonal-dipyramidal mineral containing calcium, carbon, hydrogen, oxygen, silicon, and sulfur.