The Collaborative International Dictionary
glassy feldspar
Sanidine \San"i*dine\, n. [Gr. ?. ?, a board. So called in allusion to the tabular crystals.] (Min.) A variety of orthoclase feldspar common in certain eruptive rocks, as trachyte; -- called also glassy feldspar.
Wiktionary
glassy feldspar
n. (context mineralogy English) sanidine