Titanite is typically found in calcium-rich metamorphic rocks and scattered in some granites. Its chemical formula often includes other elements (Nb, Cr, F, Na, Fe, Mn, Sn, V or Yt). Titanite has long been known as sphene. That name is now deprecated by the mineralogical authorities, but you may still hear it used by mineral and gem dealers, collectors, and geological old-timers.
Titanite is CaTiSiO5, a yellow or brown mineral that forms characteristic wedge or lozenge-shaped crystals. (more below)
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