Chapter+10

Click here for the chapter Powerpoint: [|Chapter 10-Core.ppt] //**Quartz, Malachite, Fluorite, Amethyst, Crysacola **//

Click here for the **Dynamic Earth** link. It's an **excellent** interactive site: []

**Minerals – The Building Blocks of the Earth's Crust**

If you were planning to bake a pie, what ingredients would you use for the crust? The ingredients used to make the Earth’s crust are complex. The basic ingredients are known as elements. There are 92 known elements that exist in the Earth’s crust. These elements combine with one another in a number of natural ways, creating molecules known as minerals. There are around 3,700 known minerals found in the Earth’s crust, we dozens of new minerals being discovered each and ever year.

These minerals combine to form crystals in regular and distinct patterns. Sometimes the crystals are obvious to the un-aided eye. In other occasions, it is necessary to use a microscope to observe the crystals.

**Igneous Rocks**

All rocks on Earth were initially igneous in nature. Igneous rocks form as liquid magma cools, forming crystal structured rocks. There are many different types of igneous rocks. Igneous rocks that form deep within the Earth’s crust were temperatures are very high, might take thousands of years to cool down. This causes the crystals to be much larger, such as in the case of granite. Igneous rocks formed on the surface cool down in just a matter of a few hours. The crystals in these rocks can be microscopically small. Thus, scientists divide igneous rocks into two different categories. Those which cooled below the surface, and those that cooled on the surface. Those which began their lives below the surface are called intrusive rocks, while those which cooled on the surface are referred to as extrusive rocks. ​**Sedimentary Rocks**

Over the course of millions of years, the igneous rocks are weathered down by forces of wind and water. Fine particles of dirt begin to cover the landscape. Often, these small rock particles end up being suspended in water, and find their way to the bottom of lakes, streams, and the ocean.

Slowly, the layer of sediment on the bottom of lakes, and especially on the bottom of the ocean grows deeper and deeper, reaching depths of thousands of feet. The weight of all the sediment becomes immense, pushing down on lower layers of sediment with tremendous force. In addition, a number of minerals, which act like cement, bond the sediment together, causing it to form sedimentary rock.



**Metamorphic Rocks**

Metamorphic rocks form deep within the Earth, when heat and pressure are applied to either igneous rocks, or sedimentary rocks. This heat, and pressure in essence cooks the rocks, changing their structure substantially. The rocks are partially melted, and the chemicals within them are rearranged, so that the final rock is very different than the original rock. The final state of a metamorphic rock depends on the amount of pressure the rock was subjected to, the amount of heat the rock was subjected to, and the amount of time the rock was subjected to pressure and heat. One very common metamorphic rock, is marble. Marble is formed when heat and pressure are applied to limestone for many thousands of years.