Question: What are the 3 main kinds of rocks? The 3 kinds of rocks are igneous, sedimentary, and metamorphic. Igneous rocks are either glassy, fine grained, coarse grained, or porphyritic. Volcanic rocks sometimes have holes in them from escaping gases (called vesicles). Sometimes the holes are filled with minerals, and then the rock is amygdaloidal. Rocks that have vesicles are usually fine grained like basalt. Volcanic rocks are fine grained, glassy, or porphyritic. Glassy texture is easy. …showed first 75 words of 2380 total…

…showed last 75 words of 2380 total…This is what controls cleavage in a mineral. Some minerals fracture. This is breakage along directions that are not controlled directly by the atomic arrangement. A good example of a mineral that has fracture but not cleavage is quartz. Quartz consists of silicon and oxygen arranged in a three dimensional array where there are no preferred directions of breakage. Therefore, the mineral breaks in a rough, irregular, uneven, or conchoidal fashion. This is called fracture.