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Exam 3 Additional Notes

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Ohio State University
Earth Sciences

 Where do gems come from? o Rocks: a combo of 2 or more minerals; igneous, metamorphic, sedimentary o Organisms: pearls, amber (trees), coral, shells, bones of animals, sap of trees o Synthetic: make in the lab crystals that are virtually flawless  Basic Layers of Planet Earth o Outer layer (crust of both land and ocean) o Mantle: think molten material, very viscous o Inner core: ion and nickel, solid o Outer core: more liquid, more fluidized material  The Rock Cycle o Dynamic transition through time of 3 rocks o The origin of: materials, rocks o Ultimately gems  Gems forming in igneous environments (two types) o Some gems crystallize from magma and lava o Magma and lava: what’s the difference  Molten rock material and hot, watery fluids rich in dissolved gasses  Magma = under earth’s surface  Lava = magma that has hit the surface o Extrusive environments and rocks  Lava erupting at earth’s surface  Forms crystals in fluid and gas filled cavities (bubbles) • geodes  Cools quickly at Earth’s surface • Makes small crystals  Not a significant source of gems  MOST IMPORTANT ROLE FOR EXTRUSIVE ROCKS • Brings up to the surface gems that have already formed deeper in the mantle  Igneous rocks  Come up from volcanoes  Forms a bubble  Crystals grow inside the environment • Quartz, topaz, amethyst, agate  Most important role • Bring up crystals from depth • Once in the earth’s surface they are exposed to the elements • Weathering releases crystals • Peridot, moonstone, diamond (180-200km) o Gems forming in the mantle  Require high pressure and high temperature  Mantle minerals may be brought to the surface by tectonic activity and volcanism  Weathered and released by humans o Intrusive environments and rocks  Solidified magma near earth’s surface  Material has not been extruded by a volcano  Have long time to cool • Make large crystals  Plutons are igneous intrusions near earth’s surface • Pegmatites: the small fingers (intrusions) of a pluton • Often make it all the way to the earth’s surface • Find the best gems • Or can be exposed when surrounded country rock is eroded away  Pegmatites and gems • Extremely important source of gems • Emeralds, rubies, felspar • End phase of magma crystallization • Rare materials that are harder to bond with others, finally have to crystallize  push from pluton to pegmatite and wait until the end to crystallize o Most of gems in market lithium, beryllium and boron • Highly mobile fluid due to leftover water content o Very dynamic  water makes them liquidy  Nature’s Jewel Box • Large • Can be virtually flawless o Cool very slowly, makes cracks rare, sometimes have bubbles • Perfect as gems • Boron makes reds and greens in tourmaline • Boron and lithium make watermelon tourmaline • Beryllium rich o Beryl: emerald, aquamarine, morganite  Metamorphic Rocks o Form in metamorphic environments o Plate tectonics create metamorphic environments where rocks deform under high pressures and temperatures  Subduction zones • Cali • Plates collide and one plate dives or subducts under another  Mountain building zones (collision zones) • Plates collide and bothe plates buckle up forming mountains • Himalaya o Two types of metamorphic rocks  Regional metamorphism • Affects large areas further away from the heat and pressure action zone • Large volumes of rocks are changed in response to pressure (high) • Garnet (octahedral) and spinel, ruby (cubic) • Some heat + some pressure = regional  Contact metamorphism • Where the heat and pressure are most intense • The plates are closely colliding, where the plates are hitting • Rock melt and forms new crystals • Lapis lazuli, emeralds, diopside • Lots of heat + lots of pressure = contact Gemstone Deposits  Tourmalilne, aquamarine, topaz, garnet and apatite come from granitic pegmatite deposits, while rubies, emeralds and sapphires come from metamorphic and hydrothermal deposits the tend to be regional and cover a large are  How are gems found o Mining o Sifting though alluvial deposits o Collecting shells  Amber o Collecting from sedimentary deposits o Alluvial deposit  Washed up or carried out by water  Sedimentary deposits (2 types) o Results from mechanical or chemical weather of previous rk o Mechanical  Exposed to the elements, wind,  Disaggregation  Transport  Deposition  Known as placer deposits • Reserved for sedimentary deposits with economic impacts • Alluvial deposits that contain significant amounts of metals and gems • High density = heavy • Chemical resistance to weathering • High mechanical durability = hard • Gold, platinum, diamond, garnet, ruby, sapphire, zircons  Alluvial deposits • Rock wethered at surface • Crystals are released as grains • Mineral grains o Break into small particles o Become dissolved o Transformed to clay • Minerals that survive chemically unchanged are washed into streams • Concentrated in stream bed and along beaches • How we find nuggets  nuggets • **released by weather  Ceylon Gem Gravels • Sri Lanka • Gems collected for hundreds of years • Become concentrated in alluvial deposits • Gems weather from igneous and metamorphic rocks o Chemical  Material reacts with the water and dissolves  Dissolution of original material  Cooling or evaporation (salt)  Precipitation of new minerals  Agate (most common)  geodes  Opal  chemical sedimentary o Hydrothermal deposits  Water originates from magma bodies (igneous related), minerals that contain water in their crystal structures, or heated rain water  Under high pressure, high temps, breaks the rock, shoots upward, carries a lot of elements  Veins are fluids  Veins of minerals fill cracks  Beryl, quartz, gold  Gems crystallize from hot water solutions when the solutions encounter open spaces in rocks o Primary vs. secondary gem deposits  Primary: gems in their original rock (pegmatite)  “host” = parent rock  Secondary: gems are relocated (transported by water, wind, or ice) • Require: o Enough energy to pick up and transport particles of rock o Gems to be resistant enough to survive physical and chemical attack, so they can become concentrated in sedimentary environments o Heavier DIAMONDS  Characteristics o Green and red from radiation o Yellow, brown  nitrogen o Blue  boron o Hardness  10 o Composition  carbon o Formation of diamonds  Kimberlites o Until recently, southern African countries accounted for 98% of diamond production o American diamonds  Occasionally found in alluvial gravels • From glaciers or from Canada  Some are found in kimberlite  How rare are diamonds o In kimberlite: about 5 parts per million o Only ~20% of diamonds are gem quality o Non-gem quality diamonds are used for industrial purposes o They are rare, but there is more rare stuff out there  The four c’s of diamonds o Cut  If not cut properly, lose brilliance o Color  The less color, the more sought after/valuable o Clarity  Has to due with imperfections in the stone  Bubbles or cracks within the stone  Flawless  no inclusions or blemishes, most valuable but hard to find o Carat  .2g  a weight measure  use for the size of a stone FAMOUS DIAMONDS  Cullinan Diamond o About the size of a grapefruit CONFLICT DIAMONDS  Blood diamonds o Trade money used to fuel war o Kidnap children/people  Use them to harvest
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