Geologists classify rocks according to the processes by which they were formed. Igneous, metamorphic and sedimentary rocks have unique histories, and each category is further subdivided into more specific classes that place a rock firmly in the overall geological classification scheme.Know More
Igneous rocks are those that formed in the undercrust and later extruded to the surface. Some igneous rocks flow to the surface as molten lava, while others erupt in less viscid masses called tephra. Other igneous rocks, called plutons, rise near the surface strata but stop and gradually cool before they are exposed by erosion. Obsidian is an example of an igneous rock that emerges as lava and cools, and granite is typically formed as a pluton under the crust.
Sedimentary rock is formed after rocks of other types erode away from their beds and are transported to a common dump site. The character of sedimentary rocks is largely determined by the grains that go into it. Sandstone is formed by large, angular grains that have been compacted over time, while mudstone is usually more finely grained and forms from silt deposits.
Metamorphic rock, such as marble, usually begins as a sedimentary deposit, but its minerals undergo transformation as heat and pressure force the crystals to reform inside the rock.Learn more about Geology
Rocks are important because geologists use evidence from them to learn about what the Earth was like in the past. They allow scientists to build a historical record of the planet to learn what events occurred before people lived.Full Answer >
Copper is obtained through mining processes from copper-bearing ores such as bornite, cuprite, covellite, tenorite, chalcocite and malachite. Much of the copper mined today comes from copper ore rich deposits in countries like Canada, the United States, Zaire, Chile, Peru and Zambia. The extraction and refining of copper date back to ancient times and have been in use by humans for the last 11,000 years.Full Answer >
Buried rock fragments may be further subjected to processes of weathering that cause them to break down into smaller particles or soil, or they may become new rocks through the sedimentary process. The sedimentary process requires time and pressure to create new rocks from rock fragments and sediment.Full Answer >
Geologists classify crystals into six groups based on the number of axes and the angles of the facets, or faces, on a specimen. The science of crystallography labels the six categories as isometric, tetragonal, orthorhombic, monoclinic, triclinic and hexagonal.Full Answer >