What are coarse-grained igneous rocks?

Matthew Nyman, TERC. Is the rock generally light colored with dark crystals spread throughout? If yes, your sample is probably granite. Granite usually takes on the color of the feldspar crystals in it. Matthew Nyman, TERC. Is your rock dark colored? If yes, your sample is probably gabbro. read more

If yes, your sample is probably diorite. If you have identified your sample, return to the beginning of the rock identification key, select another rock sample, and begin the process over again. read more

Coarse-grained textures generally indicate magmas that slowly cooled deep underground. Slow cooling gives crystals enough time to grow to easily seen sizes (i.e., larger than 1 mm). The first-formed crystals tend to have regular shapes because they grow freely into the surrounding liquid. read more

Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet, surrounded by pre-existing rock (called country rock); the magma cools slowly and, as a result, these rocks are coarse-grained. read more

Coarse-grained igneous rocks (igneous tocks with large crystals) are usually formed at some depth beneath the surface. At depth, the difference in temperature between the molten rock material and its surroundings is relatively small, so this let's the molten material cool more slowly. read more