Scapolite is a name used for a group of aluminosilicate minerals that includes meionite, marialite, and silvialite. Meionite and marialite are end members of a solid solution series. Silvialite is a mineral that is very similar to meionite.

These minerals have very similar compositions, crystal structures, and physical properties. They cannot be easily distinguished from one another in the field or during hand specimen examination in a laboratory. The name “scapolite” is a term used for convenient communication. These minerals are found in small quantities in some metamorphic and igneous rocks. Their compositions are compared in the table below.

Mineral	Chemical Composition
Meionite	Ca4(Al2Si2O8)3(CO3,SO4)
Marialite	Na4(AlSi3O8)3Cl
Silvialite	(Ca,Na)4(Al2Si2O8)3(CO3,SO4)

Cat’s-eye scapolite: Some scapolite has an internal silk that causes it to form a cat’s-eye or a chatoyance. The stone on the left is a 10 x 7 millimeter oval with a very coarse silk. The silk can be seen in the stone as linear bands of black inclusions that cross the stone from left to right. The cat’s-eye forms at right angles to the silk. In the stone on the right, the silk has just the right spacing to serve as a diffraction grating and produce a beautiful display of iridescent color. Both gems were cut from material produced in India.