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Lecture 11

EPSC201 Lecture 11 Notes V2.doc

6 Pages
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Department
Earth & Planetary Sciences
Course Code
EPSC 201
Professor
Anthony Williams- Jones

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EPSC201 - Lecture 11 Notes Minerals are naturally occurring, chemically pure solids. Crystals are made up of minerals. Halite is a mineral that forms a cubic structure crystal. Halite is also common table salt, NaCl. The bonds that link the sodium and chlorine are ionic bonds, which means there was an electron transfer. The electron transfer causes the atoms to form charged substances called ions. Cation = positive ion (Na+) Anion = Negative ion (Cl-) The outer shell of both atoms want to have 8 electrons. Neutral sodium atoms have 9 elec- trons in the outer shell, so sodium gives off a electron, losing a negative charge. This makes sodium have a net 1 positive charge. The chlo- rine gains the one electron, giving it 8 total, and a net -1 charge. Atoms vary in size. The variation in size causes crystals to pack in different ways. Cations and anions want to be next to each other, and repulsed by like ions. Opposites attract, likes repulse. The shape of the crystal is determined by the size of the atoms packing around each other, called coordination. Diamonds are a very hard substance. They can scratch any other material. Diamonds can scratch glass, while copper and iron won’t be able to. They are softer then diamonds. There are no sub- stances on earth that are harder then diamonds. Diamonds don’t scratch, but they can shatter. If you hit a diamond with a hammer, it will shatter into dust. In diamonds, carbon atoms are bonding to other carbon atoms. The atoms are sharing elec- trons. All the atoms have the same elctronic configuration. This is refered to as a cavalent bond. (Sharing electrons between atoms) The Big Hole at Kimberly, South Africa, was the first mine to find diamonds. Diamonds come from deep inside the earth. They form at very high pressures, and high temperatures. These condi- tions are found at 250 km deep. Carbon at shal- lower depths forms graphite. Both diamonds and graphite are pure carbon. Even around 100 km there are diamonds forming. Diamonds are the stable form of carbon at big depths. Graphite is the stable form at shallower depths. Liquid formed at depths move upwards towards the surface. As it moves upwards it plucks off pieces of mantle. Magma helps the mantle move upwards toward the surface. Frag- ments of the solid mantle are brought to the surface by magma, which sometimes contain dia- monds. Kimberlite – fragments of mantle containing diamonds Magma – molten rock below the earths surface Discovery of diamonds in South Africa was made by a 10 year old kid. They were playing mar- bles. In Hope Town, there was a doctor who recognized these marbles as diamonds. This caused a mining rush for diamonds. Mining claims were two meters by two meters, which was very hectic. Seccil John Rhodes – bought all these small claims, and made himself a millionaire. This created the mining industry in S.A. There has been a recent discovery of diamonds in Quebec. There is speculation that there is a planet dominated by carbon. It is about twice the size of earth. The theory is that it is rich in diamonds below the surface. In graphite, the atoms are arranged in a series of planes. The planes contain the same bonds as diamonds, carbon carbon bonds, but only in the plane. A pencil is able to lay down sheet of graphite, because it breaks easily in one direction, along the plane. The planes are held together by Van der Waals forces. Impregnating other materials with graphite allow the material to slide, because the planes slide along each other. This makes the material, found in tennis rackets for example, flexible. Diamonds do not last forever, as suggested by advertising. However, the kinetics along the dia- monds to be stable for around billions of years. So they will be safe in normal conditions for a long time. If a diamond were put in the oven, with oxygen present, it will combust. Carbon + oxygen = carbon dioxide This is the combustion formula. This occurs when you burn wood. If a diamond is heated hot enough, it will combust and form carbon dioxide. Water molecules like to form weak bonds with each other, called Hydrogen Bonds. The water molecule is polar, because the oxygen is extremely electronegative, and the hydrogen is elec- tropositive. The net result is the molecule behaves as a bar magnet
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