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_06_Minerals - GEL 1 Lecture 6 Minerals Building Blocks of...

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1 GEL 1: Lecture 6 : Minerals: Building Blocks of Earth (Ch. 5) About 4000 minerals have been identified on Earth. Some minerals take the form of beautiful gems like sapphires . Sapphire is the gem name for the mineral corundum , a very hard mineral composed of Al 2 O 3 , with minor impurities of cobalt, iron or titanium that impart the variable colors. (Rubies are the same mineral with the red colors imparted by traces of chromium.) - a gem is a cut-and-polished stone that has intrinsic value and possesses the necessary beauty for use in jewelry. So gems form a particular sub-group of minerals. Some minerals have value as ores of precious metals - e.g., galena is the primary ore mineral of lead (Pb); vanadinite is the ore mineral for the element vanadium; cinnabar is the ore mineral for mercury (Hg); chromite provides chromium; native gold - an ore mineral is any mineral that has economic value and that can be extracted from the ground at a reasonable profit. And some minerals simply form rocks – there are only about 30 common rock-forming minerals Elements build minerals . . . Elements (each composed of one specific type of atom) build into minerals (specific combinations of elements), which in turn build into rocks (aggregates of minerals). Iron (Fe) and oxygen (O) are the two most abundant elements within the entire Earth, with lots of silicon (Si) and magnesium (Mg) Silicon and Oxygen are the two most abundant elements within Earth's crust - Si and O combine to make SiO 2 -based minerals called silicate minerals with smaller amounts of other elements mixed in such as iron, calcium, magnesium, aluminum, sodium, or potassium - most common rocks are silicates , since most mineral are silicates What is a mineral? naturally occurring - not synthetic inorganic solid – [organic molecules consist of C bounded to H w/ variable amounts of O, N and other elements] – also, minerals can’t be liquids or gases definable chemical composition - each mineral is unique, chemically orderly arrangement of atoms (i.e., crystal structure) - each atom and molecule has a predictable position
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2 Crystals . . . A crystal is a single, coherent sample of a mineral that has smooth, flat faces (crystal faces). Crystal form (aka crystal habit ) is the outward appearance of a mineral based on its internal arrangement of atoms - the regular, geometrical arrangement of atoms is called a crystal lattice some examples: - galena (PbS, or lead sulfide), the ore mineral for lead (Pb), is cubic in crystal habit because the Pb atoms and the S atoms fit together in a regular geometric arrangement that produces a cube - halite , common table salt, is a mineral composed of sodium (Na) and chlorine (Cl). The atoms stack in the most energy-efficient arrangement possible, building a cubic form. The large Cl atoms fit together tightly, but leave spaces big enough for smaller Na atoms to fill.
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