Lab 1 Minerals - Earth Sciences 1081b Lab 1: Minerals...

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1 Earth Sciences 1081b Lab 1: Minerals (Background Pages for Lab) Note: You are not required to print this background section of the lab. However, make sure you do download and print out the hand-in sheets at the end of the document before coming to your lab so that you can complete the assignment. OVERVIEW Minerals are the basic ingredients from which rocks are made; rocks, in turn, form the solid materials that make up the crust of the Earth as well as the mantle that underlies the crust. The chemistry of minerals reflects the pressure-temperature conditions under which they form and thus provide clues to the origin of rocks. Some minerals (and the rocks in which they are contained) are of economic importance for their beauty (e.g., opals, diamonds, onyx), industrial use (e.g., coal, mica, garnet), or metal content (e.g. chalcopyrite, hematite, bauxite). These rocks and minerals are used as resources in our material society. In this lab, we will study a few minerals and rocks, learn the properties by which they may be readily identified, learn the particular uses of these materials. Oxygen 48% Silicon 26% Hydrogen 1% Potassium 2% Magnesium 2% Others 2% Sodium 3% Calcium 3% Iron 5% Aluminium 8% Figure 1: Elements present in the Earth’s crust. The two most common elements are silicon and oxygen. It is not surprising then that the most common minerals that are found on earth are “silicate” minerals that contain both silicon and oxygen as their basic building blocks. MINERALS Every mineral has either a fixed chemical composition or a composition that varies only within fixed (and known) limits. Furthermore, every mineral has a definite crystal structure. These properties may or may not be particularly useful in identifying minerals. Most often, we use obvious physical properties to identify the common minerals. Some of the more useful physical properties for this purpose are listed below.
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2 Hardness By definition, the hardness of a mineral is its resistance to abrasion (which is actually a measure of its strength of chemical bonding). The approximate hardness of a mineral may be determined by testing it against common objects: glass, knife, copper penny, fingernail, etc. In the 19th century a German mineralogist by the name of Frederick Mohs assigned arbitrary numbers, from 1 to 10, to ten well-known minerals of different hardness. Mohs Scale of Hardness is one of the most useful tools by which we identify minerals (bear in mind that the scale is arbitrary, with no fixed interval between numbers). You can test the hardness of a mineral by scratching it with another mineral (or common material/object/tool) with a known hardness value. For example, if a mineral can not be scratched by a penny (hardness = 3) but can be scratched by a knife (hardness = 5) that mineral must have a hardness between those two values (as would be the case of fluorite, with the hardness of 4). The basic scale (with standard minerals and additional materials/tools of known hardness that can be used for testing). Note also
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Lab 1 Minerals - Earth Sciences 1081b Lab 1: Minerals...

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