Scapolite Group (Meionite and Marialite) - meionite: (Ca,Na)₄(Si,Al)₁₂O₂₄(CO₃,SO₄,Cl)

Habit: Bluish, brown, orange brown, colorless, violet, greenish or white. Crystals prismatic, typically with flat pyramidal terminations and striated; also granular or massive. Vitreous, resinous or pearly luster; transparent to opaque. White streak.

Environment: Found in regional and contact metamorphic rocks, skarns, pegmatites, altered mafic igneous rocks and volcanic ejecta.

Etymology: Named in 1800 from the Greek skapos, meaning "rod," and lithos, meaning "stone." The scapolite group is made up of two end members, meionite and marialite.

Scapolite was originally thought to be a single mineral, a calcium aluminosilicate, and the term is still used to describe its gemstone varieties. Now the group is defined as a series of closely related tetragonal aluminum silicates from calcium-bearing meionite to sodium-bearing marialite. Pure end members of this series do not form in nature. Several mineral names in this group, such as wernerite and mizonite, are no longer used.