English: Igneous rocks form by the cooling and crystallization of hot, molten rock (magma and lava). If this happens at or near the land surface, or on the seafloor, they are extrusive igneous rocks. If this happens deep underground, they are intrusive igneous rocks. Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy.

Syenite is an intrusive igneous rock. It is similar to granite and gabbro in that is has phaneritic texture, with all or almost all crystals between 1 millimeter and 1 centimeter in size each. Phaneritic texture forms as a result of relatively slow cooling of magma deep underground.

Syenite has a chemical composition between that of granite's felsic chemistry and gabbro's mafic chemistry. Syenite is an example of an intermediate igneous rock, which has 52 to 65% silica (= SiO2 chemistry) (intermediate has also been defined as 55 to 65% silica). Intermediate igneous rocks are sometimes light-colored, sometimes dark-colored, and sometimes have medium colors.

The mineral content of syenite is dominated by feldspar with little to no quartz. Syenite is defined as alkali feldspar-rich, with little to no plagioclase feldspar. The minor plagioclase feldspar component is often intergrown with the alkali feldspar to form perthite.

Geologic context: unrecorded

Locality: Golden Cycle Mine, near the town of Victor, Cripple Creek Mining District, southern Teller County, central Colorado, USA