Chemical composition -- Calcium titanium silicate.
Color -- Yellow, green, brown, red, black.
Optics-- R.I. 1.84-2.11, biaxial positive, dispersion 0.051 (strong).
Durability -- Hardness 5-5.5. Brittle. Usable in jewelry not subject to intense wear (earrings, pins, etc.).
Crystal structure -- Monoclinic.
Specific Gravity -- 3.45-3.55.
Sources -- Mexico, Sri Lanka (Ceylon), Madagascar, Brazil.
Sphene makes gorgeously brilliant, fiery gems. Clean stones larger than a few carats are extremely rare.