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Unformatted text preview: Chapter 1 Minerals and Mineraloids When most people think of minerals, they usually imagine expensive gemstones like diamonds, emeralds and sapphires, or economic minerals like silver, gold and copper. While it is true that each of these substances is a mineral, they are all relatively unimportant as far as the make-up of the Earth is concerned. At last count, there were over 4000 minerals on and in the Earth, but only a handful are considered "valuable" in terms of financial reward (e.g., $$$). Minerals that make you money are considered economic and their value is determined on the basis of aesthetic reasons (e.g., sapphires, emeralds) or technological/industrial applications (e.g., diamonds, copper, sulfur etc.). In reality, the most important minerals are those that are most common because they make up the rocks that comprise the Earth's crust. We live on the Earth's crust. The common minerals are called rock-forming for obvious reasons. One of the most important of the rock-forming minerals is quartz (SiO 2 ). Almost every sand grain on the beaches at Dauphin Island, Gulf Shores and Fort Walton is a fragment of a quartz crystal, a major component in continental- forming rocks like granite. Quartz isn't particularly valuable in financial terms, but where would we be without it? Figure shows several schematics of crystals. From: Ford, W., 1932. Dana's Textbook of Mineralogy. John Wiley and Sons, New York, NY, 851p. Chapter 1: The minerals 2 Now that you have been introduced to the variables that make a mineral valuable, it is probably a good idea to discuss what makes a mineral a mineral. Geologists consider a mineral to be a naturally occurring, inorganic solid that is characterized by a unique chemical composition and a definite crystal structure. This definition excludes a number of man-made substances commonly passed off as minerals including cubic zirconium (an inexpensive diamond substitute), synthetic corundum (red ruby and blue sapphire stones commonly found in high school graduation rings), and industrial diamond (a valuable abrasive). It also excludes a variety of natural substances that are found in and on the Earth. Some of these materials, such as chalcedony (SiO 2 ) and opal (SiO 2 H 2 O) are non-crystalline (i.e., they lack a definite crystal structure much like window glass). Others, such as bauxite (Al 2 O 3 ) and earthy limonite (FeOOH), are characterized by significant variation in chemical composition . Otherwise, they satisfy the definition of a mineral. Geologists call these substances mineraloids. Another naturally occurring substance that is not considered to be a mineral is amber. Amber is fossilized tree sap and is therefore organic....
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This note was uploaded on 02/04/2012 for the course GLY 111 taught by Professor Haywick during the Fall '11 term at S. Alabama.
- Fall '11