This image is of an igneous rock, specifically an igneous intrusive rock called granite The rock was sliced very thin, mounted on a slide and viewed in a polarizing light microscope. In a photomicrograph, different minerals have different colors and shapes. The gray and black striped crystals are plagioclase, the blobby gray ones are quartz and the colored segmented ones are mica. Geologists like to use photomicrographs because the minerals are more identifiable. The textures are also easier to recognize, which gives the scientists clues about the rock’s formation. All this makes a rock easier to identify.
Thomas Bresson. commons.wikimedia.org/wiki/File:Thomas_Bresson_-_Granite_vu_au_microscope_%28by%29.jpg. CC BY 2.0.