Types of Rocks
Rocks are all around us. They make up the crust of the Earth and are found on the surface of the Earth.
Rocks can be classified according to how they are formed.
Igneous rocks are formed from rock that has melted and becomes a liquid rock that cools.
Sedimentary rocks form from deposits that build up over time.
Metamorphic rocks form from other rocks when exposed to heat and pressure.
Igneous rocks form when heat from inside the earth melt rock. This molten rock can cool inside the earth or on the earth's surface.
Intrusive igneous rocks cool inside the earth and generally have medium to large crystals.
Extrusive igneous rocks cool on the earths surface and usually have smaller crystals.
Let's review a couple of common igneous rocks.
Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth's surface or under the ocean. The particles that form a sedimentary rock are called sediment and may be composed of minerals or organic matter.
Sedimentary rocks can be subdivided into four groups based on the processes responsible for their formation: clastic sedimentary rocks which form from fragments of pre-existing rocks
Chemical sedimentary rocks form by precipitation of minerals from water. Precipitation is when dissolved materials come out of the water, and organic sedimentary rocks such as coal, and some limestones, which form from the accumulation of plant or animal debris.
Clastic sedimentary rocks are subdivided according to the dominant particle size.
These particle sizes are ranked from smallest to largest
Clay is the smallest then silt Sand Gravel pebble Boulder
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and silt-sized particles of other minerals, especially quartz and calcite.
Shale is very fine grained
Sandstone is a clastic sedimentary rock composed of sand-sized grains of mineral, rock, or organic material. It also contains a cementing material that binds the sand grains together Sandstone is one of the most common types of sedimentary rock and is found in sedimentary basins throughout the world.
A conglomerate rock is a coarse-grained clastic sedimentary rock that is composed of pebbles, cobbles, and boulders. The space between the clasts is generally filled with smaller particles and calcite or quartz cement that binds the rock together
Limestone is an organic sedimentary rock that is often composed of the skeletal fragments of marine organisms such as coral. About 10% of sedimentary rocks are limestones.
Metamorphic rocks are formed from other rocks that are exposed to heat and pressure. Metamorphic rocks do not melt but the heat and pressure change igneous,sedimentary and even other metamorphic rocks into a new type of rock.
Foliated metamorphic rocks have their crystal in stripes.
0 comments:
Post a Comment