Rocks are classified into 3 different groups. Those groups are:
1. Igneous.
These rocks form from volcanic magma. The lava cools and solidifies, and these rocks begin to form. The lava can either come from an erupting volcano, or can remain underground.
Here are some examples:
This is granite. Granite is made mostly of quartz, hornblende, and feldspar. Depending on what it is made of, granite can be pink or gray or a combination of the two. It forms through the crystallization of magma under the earth's crust. It is the most common igneous rock found on the earth's surface.
This is diorite. Diorite is usually made up of white feldspar & hornblende. It is very hard and is usually dark gray or black as well as white or a combination of these colors.
2. Metamorphic.
These rocks are sedimentary or igneous rocks that have undergone some sort of change, whether that change be due to heat or pressure or some other force. They are formed under the earth's crust.
Here are some examples:
This is coal. Coal is made from organic carbon, meaning it is made from the remains of plants. It is usually a black or brown/black color. It is the most abundant fossil fuel in the US. It takes millions of years to form, as the energy from the dead plants put off heat and pressure from being underwater cause the rock to form.
This is gneiss. Gneiss is is essentially smashed diorite. Diorite being made of grey hornblende and white feldspar, causes the lines and layers of the 2 different colors. Other minerals can mix in as well.
3. Sedimentary.
These rocks are usually a build up of small pieces of other broken rocks, dirt, pebbles, or other material. They are formed on the earth's surface.
Here are some examples:
This is limestone. Limestone is mostly made from calcite, but with many other minerals and sands mixed in as well. It is formed from shells and other debris. Limestone is almost always found near water, and is especially prevalent in reefs. It is also a reliable building material.
This is coquina. Coquina is made of millions of clam-like seashells and other shells and fossils. It was originally formed along the eastern coastline of Florida.
Here's an alternative model for gneiss formation which suggests that gneiss is an authigenic rock formed in an aqueous setting in microgravity. The microgravity explains the large, precipitated mineral-grain size and the aqueous setting explains the sedimentary layering.
ReplyDeleteThe sharp isoclinal folding of comet rock occurs when differentiated Outer Oort Cloud (OOC) comet cores shrink during diagenesis, causing 'circumferential folding' which is not found in terrestrial sedimentary rock. Heat and temperature of metamorphism only converts hydrous minerals to their anhydrous counterparts but has no effect on the layering or folding (except in the case of massive granite and massive gneiss which has melted and is therefore plutonic).
Mantled gneiss domes are comet cores formed from authigenic rock (formed by precipitation of mineral grains) such as gneiss and quartzite and hydrothermal rock like schist and dolomite formed from hydrothermal fluids expelled during diagenesis of the underlying gneiss.
Core collapse of comet clusters create larger compound comets from comet mergers of multiple gneiss-dome comet cores, and smaller-grained authigenic shale forms in the higher gravity of the larger compound comet cores. The Appalachian province 'platform' is an example of a compound comet core from the OOC.
The Black Hills is a granite-greenstone compound-comet core from the Inner Oort Cloud which is a second comet reservoir which is volatile-enriched.