Ca2Al2Si4O12

Ca2Al2Si4O12 is a calcium aluminum silicate for which the empirical formula describes a composition containing calcium, aluminum, silicon, and oxygen in a 2:2:4:12 ratio. In mineralogical practice, the formula can be viewed as two formula units of CaAlSi2O6, aligning with pyroxene-like silicate structures where Si and Al occupy tetrahedral sites and calcium balances the framework charge.

Composition and structure: Si and Al occupy tetrahedral sites in a silicate framework, forming (Si,Al)O4 tetrahedra linked through shared oxygen atoms to produce a three-dimensional network. Calcium cations reside in interstitial sites within the lattice. The Si:Al ratio of 2:1 is typical for aluminous silicates, and the overall oxide composition would be balanced by the calcium cations.

Occurrence and significance: This exact composition is not widely recognized as a mineral by the International Mineralogical Association and there are no well-documented natural specimens. The formula is more commonly encountered in theoretical discussions of aluminous silicate chemistry, and it may arise in synthetic materials such as ceramics or glass-ceramics under controlled conditions. In such contexts, Ca2Al2Si4O12 can be viewed as a doubled or semi-endmember of a Ca-Al-Si-O system related to diopside-like and anorthite-like phases.

See also: Aluminosilicate, Pyroxene group, Anorthite, Diopside.