Keilhauite (also known as yttrotitanite) is a variety of the mineral titanite of a brownish black color, related to titanite in form. It consists chiefly of silicon dioxide, titanium dioxide, calcium oxide, and yttrium oxide.
Keilhauite has a chemical formula of (CaTi,Al2,Fe23+,Y23+)SiO5. It differs from titanite only in that calcium is substituted by up to 12 percent (Y,Ce)2O3.
References
Keilhauite Wikipedia(Text) CC BY-SA