orig., a rock composed of quartz, hornblende, and feldspar, anciently quarried at syene, in upper egypt, and now called granite.-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.