IGNEOUS ROCKS
Igneous rocks are formed when magma cools and crystallizes. They can be either extrusive, forming on the Earth’s surface from lava, or intrusive, forming within the Earth’s crust. The rate of cooling determines the size of the crystals in the rock, with quick cooling resulting in small crystals and slow cooling resulting in large crystals.
Examples include rhyolite and granite.
Rhyolite is a type of extrusive igneous rock that forms when silica-rich magma extrudes from a volcano and cools quickly on the surface. It’s usually pink or gray, with very small, hard-to-see grains. It’s the volcanic equivalent of granite.
Granite is a common, coarse-grained, intrusive igneous rock formed from slowly cooled magma. Its strength and durability, due to tightly interlocked mineral grains, make it ideal for construction and ornamental purposes.
SEDIMENTARY ROCKS
Sedimentary rocks form at or near Earth’s surface from accumulated sediment or by precipitation of minerals. They can be detrital, formed from eroded rock fragments, or chemical, formed from mineral precipitation. Key processes include erosion, weathering, dissolution, precipitation, and lithification.
Example include Sandstone and Limestone
Sandstone is a sedimentary rock made of sand-sized silicate grains. It forms from accumulated sand delivered by rivers, waves, or wind. It can also contain a cementing material that binds the sand grains together. Sandstone can serve as a reservoir for groundwater, oil, and natural gas. Its color varies due to mineral impurities.
Limestone is a sedimentary rock mainly composed of calcium carbonate. It forms when these minerals precipitate from water. It can contain other elements like clay, iron carbonate, feldspar, pyrite, and quartz. Limestone often contains fossils and is widely used in construction. It also produces lime when burned.
METAMORPHIC ROCKS
Metamorphic rocks are formed from existing rocks that undergo transformation due to high heat, pressure, or exposure to mineral-rich fluids. This usually occurs deep within the Earth’s crust or at tectonic plate boundaries. The original rock changes in mineralogy and structure, creating a new type of rock.
Examples include granite transforming into gneiss and Phyllite
Gneiss is a type of metamorphic rock formed from igneous or sedimentary rocks under high temperature and pressure. It’s characterized by a banded structure and consists mainly of feldspar, quartz, and mica. The banding is due to the segregation of different types and sizes of mineral grains. Gneiss forms at higher temperatures and pressures than schist.
Phyllite is a foliated metamorphic rock that evolves from slate. It’s composed mainly of quartz, sericite mica, and chlorite. Its defining feature is its reflective sheen due to fine-grained mica flakes aligned in parallel. It’s typically black to gray or light greenish-gray in color.
No comments:
Post a Comment