ludlamite

from The Century Dictionary.

• noun A hydrous phosphate of iron, occurring in bright-green monoclinic crystals. It is found near Truro in Cornwall, and is associated with vivianite in cavities in pyrite.

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

• noun (Min.) A mineral occurring in small, green, transparent, monoclinic crystals. It is a hydrous phosphate of iron.

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

• noun mineralogy A monoclinic-prismatic mineral containing hydrogen, iron, magnesium, manganese, oxygen, and phosphorus.