berilli

Berilli is a term encountered in a few contexts, most commonly as a plural or variant form referring to members of the beryl mineral group and occasionally as a surname or toponyms. The beryl group comprises cyclosilicate minerals with the basic chemical composition Be3Al2Si6O18 and a hexagonal crystal system.

Beryl occurs in a range of colors and gem varieties determined by trace-element impurities: emerald (green, chromium or vanadium), aquamarine (blue to cyan, iron), morganite (pink, manganese), heliodor (yellow), and goshenite (colorless). Beryl crystals are typically prismatic and can reach significant sizes. The mineral has a Mohs hardness of about 7.5–8, making gem-quality specimens suitable for cutting and jewelry. Beyond gemology, beryl is an important ore of the element beryllium, which has specialized industrial uses in aerospace, electronics, and nuclear applications.

The name beryl derives from ancient Greek beryllos, historically used for precious blue-green stones. When used as "berilli" in language or cataloguing, it usually denotes multiple beryl specimens or varieties. Proper handling of beryl-bearing materials during mining and processing is important because beryllium compounds can be hazardous if inhaled as dust or fumes; intact gems and specimens generally pose little risk in normal use.