Tonalite is a type of intrusive igneous rock that is primarily composed of quartz, plagioclase feldspar, and biotite or hornblende. It is similar in composition to granite but contains less potassium feldspar and more plagioclase. Tonalite typically has a light to medium gray color and a coarse-grained texture, making it easy to identify. This rock forms from the slow cooling of magma beneath the Earth's surface, allowing large crystals to develop. Tonalite is often found in mountain ranges and is associated with subduction zones, where one tectonic plate moves under another. It plays a significant role in understanding the geological history of an area.