Beryllonite is a rare mineral composed of sodium beryllium phosphate with the chemical formula NaBePO₄. It belongs to the phosphate mineral group and crystallizes in the monoclinic crystal system. First discovered in 1888 in Stoneham, Maine, USA, Beryllonite is named after its beryllium content, which contributes to its chemical uniqueness. This mineral is typically colorless or white, although it can sometimes appear pale yellow or slightly tinted due to impurities. Beryllonite is usually transparent to translucent and exhibits a vitreous (glass-like) luster, giving it a bright and clean appearance. High-quality crystals with good clarity can be faceted, but such gemstones are extremely rare.