Ca2Al2Si2O8

Ca2Al2Si2O8 is the chemical formula for gehlenite, a mineral belonging to the melilite group. Gehlenite is a silicate mineral that contains calcium, aluminum, and silicon. It typically forms in high-temperature metamorphic environments, particularly in contact metamorphosed limestones and dolomites. It can also be found in some volcanic rocks and meteorites. Gehlenite crystallizes in the tetragonal crystal system and commonly occurs as small, euhedral to subhedral prismatic crystals. Its color can range from colorless to white, yellow, or brown, and it often has a vitreous luster. The hardness of gehlenite is typically between 5.5 and 6 on the Mohs scale.

Gehlenite is a solid solution endmember within the melilite series, with other common members including åkermanite (Ca2MgSi2O8) and hardystonite (Ca2ZnSi2O8). The composition can vary, with substitutions possible for calcium, aluminum, and silicon, leading to intermediate melilite compositions. Due to its formation in specialized geological conditions, gehlenite is not an extremely common mineral, but it is significant for understanding high-temperature mineral paragenesis and the petrology of specific metamorphic and igneous settings. Its presence can indicate the degree of metamorphism and the availability of certain chemical elements in the parent rock.