Thortveitite is a mineral yttrium (Sc,Y)2Si2O7. It is the primary source of scandium. It was named after Olaus Thortveit engineer. It is grayish-green, black or gray in color.
A transparent gem quality example was found in 2004, and reported in "The Journal of Gemmology", 2008 Volume 31.
The mineral is actually a uniform mixture of oxides of silicon, scandium, and yttrium. It isn't a true compound in itself.