Sphene

Sphene (titanite)

Sphene — titanite in modern nomenclature — is a calcium titanium silicate named for its distinctive wedge-shaped crystals (Greek sphenos, wedge). Its claim to fame is optical: dispersion higher than diamond's, giving cut stones and even rough crystal faces an exceptional colored fire. Typical colors run yellow-green to brown; gem-grade material is prized despite modest hardness (5–5.5).