struct&materials

struct&materials - Earth Struct & Materials...

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This page last updated on 07-Jan-2004 EENS 204 Natural Disasters Tulane University Prof. Stephen A. Nelson Earth Structure, Materials, Systems, and Cycles Before we can begin to understand the causes and effects of natural disasters we need to have some understanding of the materials that make up the Earth, the processes that act on these materials, and the energy that controls the processes. We start with the basic building blocks of rocks - Minerals. Minerals The Earth is composed of rocks. Rocks are aggregates of minerals. Minerals are composed of atoms. In order to understand rocks, we must first have an understanding of minerals. We'll start with the definition of a Mineral. A Mineral is z Naturally formed (it forms in nature on its own [some say without the aid of humans]) z Solid (it cannot be a liquid or a gas) z With a definite chemical composition (every time we see the same mineral it has the same chemical composition that can be expressed by a chemical formula). z and a characteristic crystalline structure (atoms are arranged within the mineral in a specific ordered manner). Examples z Glass - can be naturally formed (volcanic glass called obsidian), is a solid, its chemical composition, however, is not always the same, and it does not have a crystalline structure (individual atoms in a glass are arranged randomly similar to the arrangement in a liquid). Thus, glass is not a mineral. z Ice - Is naturally formed, is solid, does have a definite chemical composition that can be expressed by the formula H 2 O, and does have a definite crystalline structure when solid. Thus, ice is a mineral. Liquid water is not since it is not solid and does not have a crystalline structure. z Halite (salt) - Is naturally formed, is solid, does have a definite chemical composition that can be expressed by the formula NaCl, and does have a definite crystalline structure, as shown below. Thus halite is a mineral. 1/7/2004 Page 1 of 15
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Important Minerals in the Earth's Crust The variety of minerals we see depend on the chemical elements available to form them. In the Earth's crust the most abundant elements are as follows: 1. O, Oxygen 45.2% by weight 2. Si, Silicon 27.2% 3. Al, Aluminum 8.0% 4. Fe, Iron 5.8% 5. Ca, Calcium 5.1% 6. Mg, Magnesium 2.8% 6. Na, Sodium 2.3% 7. K, Potassium 1.7% 8. Ti ,Titanium 0.9% 9. H, Hydrogen 0.14% 10. Mn, Manganese 0.1% 11. P, Phosphorous 0.1% Note that Carbon (one of the most abundant elements in life) is not among the top 12. Because of the limited number of elements present in the Earth's crust there are only about 3000 minerals known. Only 20 to 30 of these minerals are common. The most common minerals are those based on Si and O: the Silicates. Silicates are based on SiO
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This note was uploaded on 11/20/2010 for the course LIR 30 taught by Professor Thornley,k during the Spring '08 term at Santa Rosa.

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struct&materials - Earth Struct & Materials...

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