Others teach and work on research projects in colleges and universities. Geologists usually specialize in one or a combination of three general areas - Earth materials, Earth processes, and Earth history. Economic geologists locate Earth materials such as mineral and solid fuels. Petroleum geologists locate oil and gas deposits below the Earth's surface. Some petroleum geologists work on specific drilling prospects, while others develop petroleum-related geologic information for entire regions.
Marine geologists collect data during scientific ocean cruises.
They study formation of ocean basins, pollution, earthquake activity, and petroleum and economic mineral potential. Engineering geologists determine suitable sites for the construction of roads, airfields, tunnels, dams, and other structures. They decide, for example, whether underground rocks will bear the weight of a building or whether a proposed structure may be safe in an earthquake-prone area. Mineralogists analyze and classify minerals and precious stones according to composition and structure. Geochemists study the chemical composition and changes in minerals and rocks to understand the distribution and migration of elements in Earth's crust.