Syenite igneous rock. Syenite is an igneous rock that forms when volcanic magma solidifies under pressure in the Earth's crust. It is coarse- grained, and similar in composition to granite except that it contains little or no quartz. It is composed of feldspar, mica and pyroxene minerals. Hornblende, a silicate mineral, is responsible for the dark grains in this sample. Syenite is relatively uncommon, found mainly in a few areas of the United States and Germany. This sample measures 120 millimetres across.
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