Merriam-Webster Collegiate Dictionary - beryl

 noun  Etymology: Middle English, from Middle French beril, from Latin ~lus, from Greek beryllos, back-formation from beryllion ~, of Indo-Aryan origin; akin to Prakrit verulia, veluriya ~  Date: 13th century a mineral consisting of a silicate of ~lium and aluminum of great hardness that occurs in colorless hexagonal prisms when pure and in various colors (as green, blue, yellow, or pink) when not pure, that is valued as a source of gems, and that is the principal source of ~lium