epididymite

Century Dictionary and Cyclopedia

1. n. A silicate of beryllium and sodium, HNaBeSi₃O₈, occurring in colorless twinned orthorhombic crystals of tabular habit: found in southern Greenland. It has the same composition as eudidymite, but differs from it in crystallization.

Wiktionary

1. n. mineralogy An orthorhombic-dipyramidal mineral containing beryllium, hydrogen, oxygen, silicon, and sodium.