sanidinite

from The Century Dictionary.

• noun In petrography, phaneric masses occurring like segregations in trachytic and phonolitic volcanic lavas and sometimes ejected as bombs: composed chiefly of orthoclase feldspar with subordinate amounts of other minerals. It has been proposed by Weed and Pirsson (1895) to apply the name sanidinite to syenitic rocks composed almost wholly of orthoclase.