be3Al2Si6O18

Be3Al2Si6O18 is the chemical formula for beryl, a silicate mineral that belongs to the cyclosilicate group. The formula reflects a framework built around rings of SiO4 tetrahedra (Si6O18) with aluminum and beryllium occupying interstitial sites. Beryl crystals are typically hexagonal and can form prismatic, tabular, or massive habits.

Beryl crystallizes in the hexagonal system and commonly forms transparent to translucent crystals with a vitreous luster. It has a hardness of about 7.5 to 8 on the Mohs scale and a relatively low to moderate specific gravity, typically ranging from 2.63 to 2.87 g/cm3. The mineral shows poor cleavage and a conchoidal to uneven fracture. Its refractive indices are in the roughly 1.57 to 1.60 range, with a small birefringence, making it distinctly doubly refractive.

Color varieties of beryl arise from trace impurities. The emerald variety is green due to chromium and sometimes vanadium; aquamarine is blue from iron; morganite is pink from manganese; goshenite is colorless. These colorations can be enhanced or altered by heat treatment or irradiation in some stones.

Geologically, beryl forms in granitic pegmatites and, less commonly, in metamorphic rocks and hydrothermal environments. It is an important source of beryllium, a metal used in aerospace, electronics, and specialized alloys. Beryl gemstones are widely valued in jewelry, with emerald and aquamarine among the most prized varieties. Handling of beryl-containing dust requires caution due to beryllium’s health hazards when inhaled.