7.2: Igneous Rocks

Igneous Rocks

Igneous rocks are the only rocks that form from a liquid (or molten) state. All igneous rocks start out as molten material (magma Links to an external site. or lava Links to an external site.), which must harden to form a rock. Igneous rocks differ from one another primarily due to: 1) the composition of the molten material from which the rock is derived, and 2) the cooling process of the molten material that formed the rock. These two parameters define the classification of igneous rocks, which are simplified into the two terms: composition and texture. Igneous rock composition refers to what is in the rock (the chemical composition or the minerals that are present), and the word texture refers to the features that we see in the rock, such as the mineral sizes or the presence of glass, fragmented material, or vesicles (holes) in the igneous rock.

A person who studies igneous rocks is referred to as an igneous petrologist. A petrologist is a geoscientist that studies rocks and the conditions under which they form. An igneous petrologist is a geoscientist who specializes in igneous rocks and their conditions of formation. Like many other geoscientists, working with other disciplines is common, with a heavy influence from both math and technology. Many are employed by universities where they teach and/or do research, and at state and federal agencies, including geological surveys, like the California Geological Survey Links to an external site. or United States Geological Survey (USGS) Links to an external site.. Additional career pathways are available in the private sector including mining and natural resource extraction. Many of these career options require a college degree and postgraduate work. If you are interested, talk to your geology instructor for advice. We recommend completing as many math and science courses as possible (chemistry is incredibly important for mineralogy). Also, visit National Parks Links to an external site., CA State Parks Links to an external site., museums, gem & mineral shows, or join a local rock and mineral club. Typically, natural history museums will have wonderful displays of rocks, including those from your local region. Here in California, there are a number of large collections, including the San Diego Natural History Museum Links to an external site., Natural History Museum of Los Angeles County Links to an external site., Santa Barbara Museum of Natural History Links to an external site., and Kimball Natural History Museum Links to an external site.. Many colleges and universities also have their own collections/museums.