Chemical composition -- Zinc sulfide with iron.
Color-- Yellow to brown, orange, green, black, rarely colorless.
Optics -- R.I. 2.37-2.40. Dispersion 0.156 (extremely high).
Durability -- Hardness 3.5-4. Brittle and with six directions of perfect cleavage. Too fragile for use in jewelry (unfortunately!).
Crystal structure -- Isometric (cubic).
Specific Gravity -- 3.9-4.1.
Sources -- Mexico, Spain, U.S.
Sphalerite makes spectacularly brilliant and colorful gems and is available in large sizes, but its fragility restricts its use to collections.