Forms crystals in fluid and gas filled cavities (bubbles) geodes Cools quickly at Earth s surface Makes small crystals Not a significant source of

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1 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

2 o o 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 ( km) 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 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

3 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

4 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

5 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

6 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 diamonds Sell them illegally o Mostly western Africa, are tied to conflict diamonds Characteristics of countries Clean Diamond Trade Act o Will not buy diamonds without reputable dealers o Must have certificate Kimberly Process BERYL: HISTORY OF NAMES Beryl: from ancient Greek, beryllos, originally applied to all green stones Emerald: from Greek, smaragdos, green (vivid green) Aquamarine: Latin, aqua marina, sea water (cloudy blue must be heat treated to get beautiful ones) Heliodor: (golden) Greek, helios, Sun; good for cabochons

7 Morganite: mostly pink, also violet, peach, salmon, After J.P Morgan American financer CHARACTERISTICS o Composition Beryllium aluminum silicate, Hardness: Colors: various violet most rare Crystals: hexagonal Luster: vitreous Pleochroic LOCATION o Pegmatites (+++) o Hydrothermal deposits (++) Columbian emeralds o Metamorphic rocks (+) Not great for gemstones, not clear o Columbia, Brazil, Madagascar o Colorado, Idaho, Maine, North Carolina, California East hydro or meta West pegmatites Columbian Emerald Deposits o Located in the Andes mountains of SA: rugged terrain o Because of the tectonic setting o West coast of SA is bordered by a Subduction zone Hot fluids make veins, in veins where we find best gems o Hot rocks for emeralds are strongly deformed sedmentary rocks (folded and fractured) Ideal conditions o Hydrothermal fluids penetrated the cracks in the deformed sedimentary rocks o Chivor Mine Rugged topography Folded and faulted Veins of calcite conentraded along folded layers Emeralds occur in calcite veins or in cavities Brazil o Pegmatites not related directly to Subduction zone Plate on subduction zone is melting underneath and make magma want to come up on east, make pegmatites o No Subduction in east coast of SA o o Feels the magma regime from other side Minas Gerais Largest gem-bearing pegmatite district in world

8 Found in alluvial deposits, but hard to find source Difficult terrain slowed discover of the first pegmatite Long mining history 1500s tourmalines, aquamarine, alexandrite, kunzite (rare as a gemstone, purple, degrades with light), topaz o Pegmatite formation Plutons pegmatite (fingers) stretch to the earth Granitic Felds[ar, quartz, mica crystals Madagascar o Pegmatites o Beryl (aquamarine, emeralds, morganite), tourmaline, some others rare and exotic o Sakavalana pegmatite Pezzottaite (new gem) already exhausted Closely related to beryl, but different crystal structure Beautiful deep reddish pink; dubbed raspberyl or raspberry beryl Ortorombic structure (don t need to know) o Famous emeralds Hooker Emerald: (75.47 carats, square, 27mm on each edge Found in Columbia; shipped to Europe by Spanish Conquistadores (1700s) Gift to USNM, 1977 Spanish Inquisition Necklace Composed of large emeralds and diamonds, fashioned in India Bequeathed to USNM 1972 The Marie-Louise Diadem Gift to Napoleon Bonaparte to Empress Marie-Louis Orginially set with 79 emeralds and 1006 mine-cut diamonds in silver and gold Emeralds removed and sold in other pieces of jewlery replaced with turquoise Purchased for USNM CORUNDUM Until about 1800s rubies were not recongnized as a variety of corundum Ruby: latin rubeus, hexagonal Garnet and spinel not corundum Sapphire: sapphires, blue ; lapiz not sapphire Characteristics o Aluminium oxide o Hardness of 9

9 o Yellow, colorless, brown, green, ect purple o Hexagonal o Vitreous (like glass) o Pleochroic ORIGIN OF RUBIES AND SAPPHIRES Rubies o Primary sources: igneous rocks; pegmatites (++), metamorphic rocks (+) o Secondary: alluvial deposits; more economical to mine o Myanmar (burma), Thailand, Sri Lanka (Ceylon) Sapphires o Primary sources: igneous rocks; pegmatites (++), metamorphic rocks (+) o Secondary: alluvial o Sri Lanka Myanmar, Thailand Australia, Tanzania, Kenya Nigeria, Madagascar, Montana Montana Yogo Sapphire o Characteristics cornflower blue color o Hard to get out, not many o Homemade operations to get them out, nothing too big o Very clear, not heat treatment Sri Lanka (formerly Ceylon) o Primary: metamorphic and igneous rocks that make up the majority of the bedrock of the country o Alluvial sediments that are present from the surface only tens of meters deep o ~ 20% of the landmass of Sri Lanka may be gem bearing Famous Stones Star of Bombay: deep blue star sapphire Star of India: light blue star sapphire British Crown Jewels: Stuart sapphire and Black Prince ruby o Don t forget about the diamonds in the crown and staff TOPAZ Possibly after the island of Topazos in the Red Sea In ancient times, all yellow and golden-brown gems were called topaz Sometimes called precious topaz or imperial topaz Shiny, can be highly radiating; carries radiation (London Blue) Characteristics o Aluminum fluorohydroxysilicate o Hardness of 8 o Yellow, orange, colorless, red-brown, blue, pink, red, violet, green o Orthorhombic o Vitreous o Pleochroic Origin

10 o Formed as fluorine-bearing vapors are given off in the last stages of solidification of igneous rocks o Primary: cavities in rhyolite (extrusive rocks from volcanoes) UTAH o Secondary: pebbles in stream (alluvial) o Sources: Brazil, Sri Lanka, Myanmar SPINEL From latin spina, little thorn (spine) referring to sharp points on octahedral crystals Red spinel often confused with ruby Characteristics o Oxide o Hardness of 8 o Many colors; pure black is rare o Cubic (often octahedrals) o Vitreous Igneous (+), metamorphic (+++) Contact metamorphism subduction zones, Famous spinel o Black Prince s Ruby Thought to be ruby Polished, never cut o Timor Ruby Polished, never cut o Grand Imperial Crown (Russia) Uncut, polished Very clear, large GET NOTESS***************************************************** Cryptocystalline: so fine-grained that individual crystals are not visible with regular microscope; requires special microscope Microcrystalline: so fine-grained that individual particles are not visible in hand sample; regular microscope Macrocystaliline: crystals large enough to see with unaided eye Present in igneous, met, and sed envir Commonly intruded so show many different optical phenomena Chemically and physically resistant at Earth s surface Amethyst colorless Feldspar Group o Most abundant mineral Continental and oceanic crust o Vary in chemistry silicate o Present in all rock environments o Fairly resistant to weathering

11 o Alters to clay o 1)K-feldspar Orthoclase: Greek: to break straight Rare, clear feldspar Yellow Amazonite Derived from amazon Opaque Light green/blue-green o 2) Plagioclase feldspar Moonstone: translucent, light, milky blue, soft iridescence (shimmer) Labradorite: deep blue/green iridescence (metallic hues) google difference of iridescence and opalescence o 3) Interference effects Opalescence (play of colors) Light is scattered by layered structure of silica spheres in opal Iridescence light is scattered by intergrowth of more than Olivine Group o Mantle o Nor resistant to weathering, alters to talc o Color: yellow-green o Hardness: o Vitreous, greasy luster o Chemistry: silicate o Peridot is the main gem variety in ig/met environments, less common in sedimentary environments Garnets o Garnet is grain in latin and pomegranate seed, deep red o Subduction zones, mountain building, remelts rocks and forms soccer ball shaped o Blue is rare; color changing depending on light source not pleochroism Garnet is isometric so only one RI o Igneous(+) and metamorphic (+++) o Common in secondary gem deposits o Gather in gravels and alluvial deposits Only responsible for stuff covered in class Know that tourmaline grow in pegmatites Lithium, boron, beryllium only found in pegmatites

12 Know how they form, why is Columbian (west side close to Subduction zone, folding and fracturing) hot fluids, veins, hydrothermal East side pegmatites Topaz grows in Utah volcanoes, lava, grows in pockets Chemical names? NO know color if it has a lot of iron ect.. Know the stones that have for sure colors like emeralds and rubies and star of India Know name and where famous gems are in bold on slides MAKE A TABLE TO COMPARE GEMS