phillipsite

from The Century Dictionary.

• noun In mineralogy, a hydrous silicate of aluminium, calcium, and potassium, commonly found in cruciform twin crystals.

from the GNU version of the Collaborative International Dictionary of English.

• noun A hydrous silicate of aluminia, lime, and soda, a zeolitic mineral commonly occurring in complex twin crystals, often cruciform in shape; -- called also christianite.

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

• noun mineralogy A mineral of the zeolite group, a hydrated potassium, calcium and aluminium silicate with monoclinic crystals.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a group of white or reddish crystalline minerals of the zeolite family consisting of a hydrous silicate of calcium and potassium and aluminum