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Rocks & Minerals NOTES Pages 1 - 3 Key Concept #1 What is a mineral? It is a naturally occurring substance which has a inorganic definite chemical composition What would be the opposite of this? man-made organic random composition ESRT Mineral Chart Click Here Are They Minerals??? Pearls N O WHY??? They’re Made by a Clam or Oyster IT’S ORGANIC Is it a Mineral? WOOD? WHY?? IT’S MADE FROM TREES AND ORGANIC ARE THEY MINERALS? DIAMONDS YES!! WHY?? NOT MAN MADE NATURALLY FOUND PURE SUBSTANCE OF UNIFORM COMPOSITION NOT ORGANIC IS IT A MINERAL? STEEL NO!!!! STEEL IS MAN MADE AND ISN’T NATURALLY OCCURING How Many Minerals are There?? T There are thousands of minerals but ONLY TWELVE OF THEM ARE COMMON. QUARTZ - Hardest common mineral Key Concept #2 What causes minerals to have different physical properties? their internal arrangement of atoms atom arrangements Key Concept #2 Give an example of two minerals which have the same chemical composition but different physical properties Click Here What causes the differences btn graphite and diamonds? How Do Minerals Form? Cooling Magma and Lava Mineral Crystals Precipitation of minerals out of Sea water – minerals in magma are dissolved by water and as the water cools the minerals drop out of the water and sink to the bottom Key Concept #4 Minerals have a definite chemical composition. What two elements, by mass, make up the greatest percentage of the Earth’s crust? oxygen silicon Key Concept #4 Minerals have a definite chemical composition. These two elements combine to form MOST MINERALS silicates (SiO4)- any mineral that has silicon and oxygen in them Key Concept #4 Minerals have a definite chemical composition. They combine in a specific structure called a: silicon-oxygen tetrahedra Silicate Factory Key Concept #3 The Main Physical Properties Used to Identify Minerals Color a poor indicator minerals can be multiple colors Ex: Quartz Key Concept #3 The Main Physical Properties Used to Identify Minerals Streak themore powder reliable formthan of a color mineral Pyrite and Gold Pyrite – green black streak Gold They have the same color but the streaks are different. So streak can be more helpful than color because two minerals may share the same color but they can have different color streaks Key Concept #3 The Main Physical Properties Used to Identify Minerals Hardness resistance to being scratched It is NOT the same as breaking! For example: You can break glass easily with steel. However, steel will not scratch glass. Key Concept #3 The Main Physical Properties Used to Identify Minerals Hardness MOH’S SCALE OF HARDNESS Hardness Mineral Hardness Mineral 1 (softest) TALC 6 ORTHOCLASE 2 GYPSUM CALCITE FLUORITE 7 QUARTZ TOPAZ CORUNDUM APATITE 10 (hardest) 3 4 5 8 9 DIAMOND Key Concept #3 The Main Physical Properties Used to Identify Minerals Luster how light reflects off a mineral metallic 1. Looks like a Metal 2. Reflects most light off the surface 3. USUALLY LEAVES A DARK STREAK non-metallic 1. Looks earthy, waxy, greasy or brilliant 2. Light is absorbed or passes through the mineral Key Concept #3 The Main Physical Properties Used to Identify Minerals Cleavage the mineral breaks in a predictable pattern because of its arrangement of atoms Key Concept #3 The Main Physical Properties Used to Identify Minerals Fracture the mineral breaks randomly Magnetism Magnetite – common mineral that is magnetic REACTION TO ACID Reaction to Hydrochloric Acid – determines there is calcium carbonate CaCO3 in the Mineral. DOUBLE REFRACTION AN IMAGE WILL APPEAR TO BE DOUBLED WHEN LOOKING THROUGH A CLEAR CRYSTAL OF CALCITE CRYSTAL SHAPE Shape of the geometric pattern - Not always visible because the crystals do not - always have the space to grow; they bond to each other and individual crystals are not visible. Ex: Quartz individual crystals are hexagonal (6 sided) Density Density = Mass/Volume **** THE BEST WAY TO IDENTIFY A MINERAL BECAUSE THE DENSITY WILL NOT CHANGE WITH THE SAMPLE SIZE AND WILL NOT BE AFFECTED BY SMALL IMPURITIES. EVERY MINERAL WILL HAVE IT’S OWN DENSITY SPECIFIC GRAVITY Comparison of the minerals density to the density of water. ****If a mineral has a specific gravity of 4 then the mineral is 4 times more dense than an equal volume of water.