Crystal system Pseudo-isometric
Transparency Transparent to opaque
Luster Vitreous
Fracture Conchoidal
Cleavage Poor
Specific Gravity 2.45-2.50
Hardness 5.5 to 6
Optical Character Single Refractive
Refractive index 1.508
Dispersion 0.010
Fluorescence bull blue
Chemical Formula KAlSi2O6
Comments Attacked by acids
Streak White

Leucite (LEW-site), a potassium aluminum silicate with the formula KAlSi2O6, is colorless or grayish. The name is from the Greek leukos meaning "white", because of the color of the crystals. An alternate name is amphigene.

Leucite exhibits strong anomalous double refraction and sometimes a weak birefringence (.001). It is a pseudo cubic material at ordinary temperatures and is isometric above 625°C (tetragonal below 625°). It often appears to have a high degree of dispersion, but this color is caused by interference of light in thin, repeated twinning lamellae.

Small, colorless faceted stones have been cut from the trapezohedral crystals, mainly from volcanic rocks of the Alban Hills area of Italy. Other sources are Germany and the United States.

Leucite is heat resistant and touch; it cuts and polishes well on lucite with cerium oxide. Polishing should be done with a thick slurry, and the lap should be kept wet. Crown angles of 40° to 50° and pavilion angles of 43° are effective.