wavellite

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A colorless to greenish yellow or black mineral, Al₃(PO₄)2(OH)₃·5H₂O, having finely acicular, radiating crystals and sometimes mined for the extraction of phosphorous.

from The Century Dictionary.

• noun A hydrous phosphate of aluminium, commonly found in radiated hemispherical or globular crystalline concretions from a very small size to 1 inch in diameter, and of a white to yellow-green or brown color. See cut under radiate.

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

• noun (Min.) A hydrous phosphate of alumina, occurring usually in hemispherical radiated forms varying in color from white to yellow, green, or black.

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

• noun mineralogy A hydrated aluminium phosphate, Al3(PO4)2(OH,F)3·5H2O, sometimed mined as a source of phosphorus.