euclase

from The Century Dictionary.

• noun A very brittle mineral of a pale-green color and high luster, crystallizing in prismatic crystals belonging to the monoclinic system.

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

• noun (Min.) A brittle gem occurring in light green, transparent crystals, affording a brilliant clinodiagonal cleavage. It is a silicate of alumina and glucina.

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

• noun mineralogy A monoclinic beryllium aluminium hydroxide silicate mineral, a product of the decomposition of beryl in pegmatites.