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| November 2009 |
| Billie Silvey |
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| Metamorphic Extreme heat or pressure operating on sedimentary rock can change it into a metamorphic rock. Examples of these include tin, sulphide, copper, silver, lead, zinc, antimony, mercury, iron and manganese. |
| Rocks and Minerals |
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| The stuff the earth is made of is all one, but it goes through changes from one form to another as shown in the diagram above. Minerals are the solid crystalline substances formed by natural and largely inorganic processes. Rocks are aggregates, or combinations of minerals formed by natural forces acting on those minerals.
There are three major types of rocks, based on the way they are formed. They come into being, are changed into other forms and break down into yet others in a cycle that has continued since the earth began. |
| Igneous Igneous rocks are formed when volcanoes erupt or rock crystallizes from magma or lava. Magma rises because it is less dense than surrounding rocks. Granite, the most common type of igneous rock, covers 85% of the earth’s crust. Rising from deep within the earth, granite is basically gray with black and white grains. The white grains are quartz and the black, micas. Other igneous rocks include obsidian, basalt, and pumice. |
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| Sedimentary At or near the surface of the ground, at lower temperatures and pressures, igneous rock is broken down by weather and transported to rest in layers of sediment particles. There it is converted into rock by cementation or compaction. Examples of sedimentary rock include sandstone, limestone, shale and chalk, slate, marble and quartzite. |
| When metamorphic rock melts, it rises as magma and the process begins again. |
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