The Collaborative International Dictionary of English v.0.48:

Syenite \Sy"e*nite\, n. [L. Syenites (sc. lapis), from Syene,
   Gr. ?.] (Min.)
   (a) Orig., a rock composed of quartz, hornblende, and
       feldspar, anciently quarried at Syene, in Upper Egypt,
       and now called granite.
   (b) A granular, crystalline, ingeous rock composed of
       orthoclase and hornblende, the latter often replaced or
       accompanied by pyroxene or mica. Syenite sometimes
       contains nephelite (elaeolite) or leucite, and is then
       called nephelite (elaeolite) syenite or leucite
       syenite.
       [1913 Webster]