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

A silicate of alumina and glucina occuring as light green, transparent crystals with a brilliant clinodiagonal cleavage. Named after the Greek word "euklas", in French "euclase", meaning "to break", because it is so brittle.

Euclase is a beryllium aluminium hydroxide silicate mineral (BeAlSiO4(OH)). It crystallizes in the monoclinic crystal system and is typically massive to fibrous as well as in slender prismatic crystals. It is related to beryl (Be3Al2Si6O18) and other beryllium minerals.