Inferring Rock Formation Through Texture and Mineral Composition

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Answer:

Sedimentary Rocks:

For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock. This type of rocks are better known as sedimentary rocks. Some examples include the following:

1. Sandstone rocks are sedimentary rocks made from small grains of the minerals quartz and feldspar. They often form in layers as seen in this picture.
2. Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of evaporated seas and lakes and from sea animal shells.
3. Shale rock is a type of sedimentary rock formed from clay that is compacted together by pressure.
4. Conglomerate rocks are sedimentary rocks. They are made up of large sediments like sand and pebbles. The sediment is so large that pressure alone cannot hold the rock together; it is also cemented together with dissolved minerals.
5. Gypsum rocks are sedimentary rocks made up of sulfate mineral and formed as the result of evaporating sea water in massive prehistoric basins.
There are three types of sediment:

• Clastic
• Chemical
• Biochemical

Most sediments are produced when rocks or minerals interact with the hydrosphere (and biosphere) near Earth's surface. Sediments generally are moved through the Earth system and eventually settle under the force of gravity. Influenced by grain size, mineralogy, or grain orientation, sediments form layers or strata, which tend to form in horizontal "beds".

Clastic Sediments

Clastic sediments are composed of fragments or grains (or clasts) of other rocks and minerals. We classify clastic sediments based on their grain size:

Information in the Clasts:

The history of the clasts that eventually lithify into a sedimentary rock is reflected in grain size, degree of sorting, and mineral composition.Grain Size reflects the amount of bumping and grinding that has occurred. For example, the ...