CHABAZITE, a mineral species belonging to the group of zeolites. It occurs as white to flesh-red crystals which vary from transparent to translucent and have a vitreous lustre. The crystals are rhom bohedral, and the predominating form is often a rhombohedron with interfacial angles of 85° 14'; they therefore closely resemble cubes in appearance, and the mineral was in fact early (in 1772) de scribed as a cubic zeolite. A characteristic feature is the twinning, the crystals being in many cases interpenetration twins with the corners of small crystals in twinned position projecting from the faces of the main crystal. A flat lenticular form of crystal is also common, this variety being known as phacolite (from cbaK6s, a lentil).
The hardness is 42, and the specific gravity 2.08-2.16.
Chemically, chabazite is a complex hydrated calcium and so dium silicate. The composition is, however, variable, and is best expressed as an isomorphous mixture of the molecules (Ca,Na2) and which are analogous to the felspars. Most analyses correspond with a formula midway between these extremes, namely Chabazite occurs with other zeolites in the amygda loidal cavities of basaltic rocks; occasionally it has been found in gneisses and schists.
Gmelinite is another species of zeolite which may be mentioned here, since it is closely related to chabazite. It forms large flesh red crystals usually of hexagonal habit, and was early known as soda-chabazite, it having the composition of chabazite, but with sodium predominating over calcium (Na2.Ca) (L. J. S.)