Magma is the molten rock in the Earth's interior. It is the ** of all igneous rocks. Since the earth was mostly molten at the time of its origin, magma can be considered the beginning of the rock cycle. Igneous rocks contain information about their origins. By carefully analyzing igneous rocks and interpreting the information they contain, we can infer the processes that occur inside the Earth, and we can understand the volcanic processes that occur on the Earth's surface.
Most magma is primarily a silicate liquid, consisting mainly of silica tetrahedra that has not yet bonded together to become a silicate mineral. The chemical composition of igneous rocks tells us the origin of magma, starting with what type of rock melts within the earth to form magma, and the melting occurs in the depths of the earth. Once magma forms in the Earth's interior, its composition may change. Minerals can grow from magma and separate from it, changing the chemical composition of the remaining liquid. Alternatively, one type of magma can be mixed with another magma of a different composition. With the exception of pure volcanic glass, all igneous rocks contain minerals. These minerals provide detailed information about the chemical composition of the rock and the magma origin, cooling, and solidification conditions. Geologists perform chemical analyses of minerals to determine the temperature and pressure at which they are formed, as well as to determine the dissolved gases and chemical elements present in the magma.
Igneous rocks contain three important pieces of information**: their minerals, their overall chemical composition, and their igneous texture. The names of igneous rocks are based on a specific combination of these characteristics. Igneous rocks also contain isotopic information that can be used to determine absolute age and further characterize the origin of magma. Performing isotope and precise chemical analyses requires special equipment and expertise. Fortunately, with some basic training and practice, anyone can learn to identify the minerals, composition, and texture of igneous rocks; Name the rocks; and explain key information about its origins. The igneous texture of a rock does not depend on how it feels in the hand or whether it is rough or smooth. Igneous texture describes whether a rock contains mineral crystals or is vitreous, the size of the mineral particles, and the porosity (voids) of the rock.
The igneous rock texture tells us how the magma cools and solidifies. Magma can solidify into igneous rocks in several different ways, each of which produces a different texture of igneous rocks. Magma may remain in the Earth's interior, well below the ground, and crystallize into plutonic igneous rocks (also known as intrusive igneous rocks). Alternatively, magma may flow out to the Earth's surface in the form of lava flows. Another way igneous rocks form is when magma erupts into the air and falls to Earth in the form of pyroclastic material, also known as pyroclastic material. Lava flows and volcaniclastic material are volcanic igneous rocks (also known as eruptive igneous rocks).
Pumice is often used as an abrasive. Pumice stone is used to smooth or scrape off dirt around the house. When the pumice stone is placed in a giant washing machine with the newly produced jeans and tumbled, the result is a "stone-washed" jeans. Ground pumice stones are sometimes added to toothpaste as an abrasive to scrub teeth.
Granite can be used in buildings and statues. It's also a popular choice for kitchen countertops. Peridotite is sometimes mined for olivine, a type of peridot used in jewelry.
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