DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Pulaskite igneous rock. Pulaskite is a variety of syenite, 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. The dark mineral grains consist of amphibole silicate minerals.
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