Or phenakite, beryllium silicate, (Be2SiO4). an orthosilicate
mineral found in pegmatities and high-temperature
veins. It has hexagonal system rhombohedral crystals, and is either colorless
or glassy white, yellow, red or brown in color. It is sometimes used as
a gem. Hardness 7.5–8; relative density 3.
AND PLANETARY SCIENCE