Bytownite is a calcium-rich member of the plagioclase feldspar mineral series, with the chemical formula (Ca,Na)(Al,Si)₄O₈. It lies near the anorthite end of the plagioclase series and is considered an important mineral in geological studies. Bytownite crystallizes in the triclinic crystal system and is commonly found in igneous and metamorphic rocks. The mineral typically appears in colors such as white, gray, colorless, or pale yellow. In some cases, it may exhibit a slight iridescence or labradorescence similar to labradorite, although this is less common. Bytownite is usually translucent to opaque and has a vitreous (glass-like) luster when polished.