Earth Science 108 Final Exam

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Fool's Gold

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Pyrite
Has similar appearance to gold; distinguished by being harder, and by brownish-black or greenish-black streak

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Distinguishing characteristic: exposure to oxygen in the air develops a gray to black tarnish (silver sulfide).

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Silver

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Distinguishing characteristic: contains up to 28% iron, and is distinctly magnetic.

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Platinum

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To increase hardness and durability, ____ (mixtures) of the metals are used

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Alloys

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Sterling Silver

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92.5% pure silver (925, sterling, STER)

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Silver plating

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Silver (variable percentage, >92%) electroplated over another metal alloy (e.g., “nickel silver,” which is mostly nickel and copper).

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Very thin layer of gold electroplated to surface of a base metal

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Gold plate

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Vermeil

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Gold over sterling silver

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Gold fill

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1/20th by weight layer of gold alloy bonded over a base metal.
Gold is not easily worn off; it is about 100 times thicker than gold plating

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Pearly

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iridescent "orient"
Iridescence (“orient”) of pearls is due to overlapping plates of nacre

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Most are formed by mollusks (clams, especially oysters, snails)

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pearls

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Nacre

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Alternating layers of aragonite and conchiolin.

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Hardened tree resin (in sedimentary deposits)
Fossil resin (millions of years old):

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Amber

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Resin

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Resins are produced by conifer trees as a defense against insects and disease.
Wound is sealed off by resin.

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Copal

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Subfossil resin (thousands of years old)

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Vitreous to resinous (polished)

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Amber's luster

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Ambroid

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Natural amber pieces welded together

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Plastics

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Smell of burning plastic detected using a heated needle; specific gravity (plastics sink in a saturated salt solution).

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Origin: Aqueous mollusks

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Shell

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Composition: Carbon, C
Colors: Black, dark brown.
Streak: Brownish-black.

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Jet

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Wood fossilized with silica (chalcedony or opal)
Mostly Mesozoic-Cenozoic.

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Petrified Wood

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Dinosaur bones with pore spaces filled by silica.

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Dinosaur Bones

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Ammolite

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Aragonite shell of Cretaceous ammonite cephalopods.
Relatives of the modern Nautilus.
Shell still has mother-of-pearl layer

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Beauty

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____ is in the eye of the beholder. May be color, brilliance (sparkle), transparency, fire (rainbow effect), luster, or a combination of these factors

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Table

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Top facet, often largest

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Crown

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Top of the stone (bezel, top)

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girdle

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edge between crown and pavilion

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pavilion

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bottom of stone

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culet

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small facet at bottom of stone

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reflection

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bouncing of light off a facet (surface)

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refraction

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bending of light as it passes from substance (air) into another (gem)

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Rainbow like flashes of color in gems

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Fire

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dispersion

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(prism effect) causes fire.
seperationof white light into a rainbow of colors

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cabochon

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gem cut with rounded upper surface. a cut lacking faces

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luster

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the appearance of light as it reflects off the surface of a gem

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durability

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depends on toughness (resistance to chipping and fracturing), hardness (resistance to scratching), stability (resistance to color loss due to heat, chemical, light)

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cut

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Ideal proportions for a gem optimize brilliance and fire, and result in greater value

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color

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some colors are more desirable than others

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Flaws (inclusions, cracks) decrease value

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clarity

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carat weigth

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– If cut, color, and clarity are equal between two stones, the larger one will be more valuable.

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rarity

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– People often desire things that are rare.
– Supply and demand.
• Limited quantity available = higher price.

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fashion

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– Value is sometimes governed by what’s in fashion (example: today blue topaz is hot; diamonds have long been in demand)

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portability

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– Many gems have a high value compared to their volume and weight (many are more valuable by weight than gold).
– Important in politically unstable areas where people are forced to flee on short notice and need a source of cash

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metamorphic

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in rock changed by heat and pressure

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igneous

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• Some gems crystallize from magma.
– Either in molten igneous rock or in bubbles of dissolved gases.
– Examples: Zircon, topaz, beryl

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pegmatites

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Unusual igneous bodies containing large crystals

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hydrothermal deposits

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involve water derived from the cooling of magma bodies or heated water

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one of the most abundunt minerals in the mantle

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olivine (peridot)

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alluvial deposits

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sedimentary environments
placer deposits

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When rock is weathered at the Earth’s surface, crystals are released as grains.
• Minerals that survive chemically unchanged are washed into streams; they become concentrated (partly because of high density) in stream beds and along beaches.

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Alluvial deposits

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Plate tectonics creates _______ environments having high temperatures and/or pressures.

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metamorphic

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shell of ancient cephalopod mollusks

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ammolite

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synthetic gem processes

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– Some examples of processes:
• Flame fusion (Verneuil) process.
• Hydrothermal process.
• Flux growth process.
• Ceramic techniques

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idiochromatic

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"self-colored" gems due to color-causing elements that are part of the chemical composition.
Example: Rhodolite garnet.

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“Other colored” -due to impurities (Fe, Mn, Cu, Ni, Co, Ti, V, Cr, etc.).
Example: Corundum:
< 1% Cr changes a colorless stone to a ruby.

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allochromatic

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oxidation state

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affects color
In beryl:
Fe2+ yields blue beryl (aquamarine).
Fe3+: Yellow beryl (heliodor).
Mn2+: Pink beryl (morganite).
Mn3+: Red beryl (bixbite).
In allochromatic gems, the color can be changed if the oxidation state is changed.
Yellow beryl can be heated in a low oxygen environment, reducing ferric iron (Fe3+) to ferrous iron (Fe2+) and producing blue beryl.
Heating can be done by wrapping the stone in paper and then burning the paper.

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charge transfer

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electron swapped between elements through heating
ex: In sapphire, heating transfers Fe2+ and Ti4+ to Fe3+ and Ti3+, producing a deep blue color.

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fluorescence

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luminescence under UV radiation
caused by impurities in the gem
iron inhibts flourescence

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Phosphorescence

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luminescence that continues after radiation has ceased

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pleochroism

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Different colors that gems appear to have when viewed under different lights or in different directions.
Caused by differing absorption of light rays in doubly refractive crystals

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orient

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rainbow-like color in pearls

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opalescence

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light diffraction in opal
precious opal has a distinct play-of-colors (opalescence)

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asterism

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Silk-like texture caused by needles of rutile (TiO2)
inclusions in sapphires (Star Sapphire) and rubies (Star Ruby)

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chatoyancy

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cat's eye effect (thin parallel inclusions)

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Adularescence

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bluish-white glow like a full moon

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Labradorescence

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metallic hues (labradorite)

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color centers

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imperfections in a crystal cause absorbtion of light.
Zircon containing uranium (U): Blue.
Zircon damaged by radioactive decay of U: Brownish-red.
Color centers can be removed by heating.

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collodial

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caused by light reflecting from numerous tiny inclusions in a mineral
Example: Flakes of mica in feldspar produces aventurine feldspar

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corrundum varieties

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ruby
sapphire
(strongly pleochroic)

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Sources of Rubies

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Primary source: Metamorphic rock (dolomitic marble, gneiss, amphibolite).
Secondary source: Alluvial deposits (more economically viable).

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Sources of sapphires

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Primary sources: Metamorphic rock (dolomitic marble), igneous rock (basalt, pegmatite).
Secondary source: Alluvial deposits.

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rutile

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a common mineral, titanium dioxide, TiO 2 , usually reddish-brown in color with a brilliant metallic or adamantine luster, occurring in crystals: used to coat welding rods.

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Star of Bombay

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deep blue star sapphire, 182 carats
Once owned by movie star Mary Pickford (given by Douglas Fairbanks, Jr.)

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Synthetic star sapphires and rubies introduced by Linde Corp. (1947).
Titanium oxide added to flame fusion mix to produce rutile crystals.

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Linde stars

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boule

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Synthetic crystal formed by flame fusion.
Also produced by flux growth

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verneuil process

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flame fusion

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light blue star sapphire, 563.35 carats.
From Sri Lanka, pre-1900; donated to AMNH by J.P. Morgan

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Star of India

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Star of Asia

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330 carats; large, intense color, sharp star
Purchased from a New York jeweler by Peter Buck, founder of Subway, and donated to the USNM in the name of his late wife, Carmen Lucia Buck

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Causes changes in the oxidation states of impurities.
_________ can improve depth of color by causing diffusion of impurities through the stone (reducing cloudy appearance) or by removing local color concentrations.

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Heat treatment

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Star Sapphire Legends

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Traditionally, a sapphire has been used to ward off harm to the wearer.
Special, historical significance attaches to star sapphires.
Traditionally, a star sapphire is the gem worn by explorers

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Morganite

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(pink, violet, peach, salmon Beryl): After J.P. Morgan, American financier

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silicate minerals

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quartz, garnet, beryl, peridot

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Beryl

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Usually occurs in veins or pegmatites (igneous rocks).

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Emerald

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occurs as hydrothermal growth in limestone; in mica schist and gneiss (metamorphic).
Secondary source: Alluvial gravels.
Grown in laboratory by flux method (Chatham, since 1940; Gilson) or by hydrothermal method (Linde)

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emerald cut

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(step cut) was developed because emeralds are prone to cracking when bumped.
Most emeralds contain inclusions and cracks.
Green oil can make fractures and flaws less obvious, and enhance general appearance of the stone.

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Marie-Louise Diadem.

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Gift of Napoleon Bonaparte to Empress Marie-Louise (wedding present, 1810).
Originally set with 79 emeralds and 1006 mine-cut diamonds (700 carats) in silver and gold.
Part of a set that included a necklace, comb, belt buckle, earrings.
Set passed to the Hapsburg family.
Purchased by Van Cleef & Arpels, 1953.
Emeralds removed and sold in other pieces of jewelry; replaced with turquoise.
Purchased for USNM by Marjorie Merriweather Post, 1971.

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argentum

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latin for silver

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origin of color

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chemical, physical, optical

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plagioclase

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feldspar with sodium or calcium

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aventurine

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calcium rich plagioclase

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Various forms of cryptocrystalline and fine-grained quartz

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chalcedony

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flint

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fine grained quartz. a form of silica resembling chalcedony but more opaque

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rock crystal

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From Greek, krystallos, ice

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amethyst

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From Greek, amethystos, not to intoxicate (ancient belief was that wine drunk from an amethyst cup would not cause intoxication)

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citrine

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From old French, citron, yellow

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chalcedony

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Possibly from Chalcedon, an ancient seaport in Asia Minor

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carnelian

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From Latin, carnis, flesh, referring to the red color

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prase

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From Greek, prason, leek, in allusion to its green color

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Formation of _____ from amethyst is common. Often done by using a wheelbarrow to immerse crystals in sand within a fire.
Crystals are heated to a high enough temperature to change the oxidation state of iron in the mineral

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citrine

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A few crystal types have polar axes instead of a symmetry center.
The opposite axes have different properties.
Pressure exerted at the ends of a polar axis causes electrons to flow to one end (producing a negative charge), and a positive charge is induced at the other end

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piezeoelectric

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___ and ____ are strongly piezeoelectric

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tourmaline and quartz

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Cryptocrystalline quartz

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chalcedony

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carnelian color

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Brownish-red to orange quartz

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tiger's eye quartz

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Chatoyant (with asbestos needles); gold-yellow, gold-brown

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cryptocrystalline

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composed of crystals that can be distinguished individually only by the use of a polarizing microscope

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Obsidian

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Origin of name: After a Roman, Obsius
Composition: Amorphous silica glass, mostly SiO2

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cochodial fracture

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important for making arrowheads, knives, etc

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Occurs in sedimentary rocks in many areas of the world

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opal

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Occurs in igneous and sedimentary rocks worldwide

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Chalcedony and fine-grained quartz

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Named for its olive-green color (due to iron)

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olivine

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Ancient name was topazion (topaz), derived from the island of Topazos (now Zabargad); called topaz until the 18th century.

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peridot

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chrysolite

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From Greek, chrysos, gold

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basalt

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peridot-rich rocks

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a range of silicate minerals in which silicate tetrahedra form single chains

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pyroxene

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a range of silicate minerals in which silicate tetrahedra form double chains

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amphibole

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spodumene

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a pyroxene, strongly pleochroic

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The most important gems among the pyroxenes and amphiboles

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jade

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“Jade” includes two unrelated mineral species, _____ (a pyroxene) and _____ (an amphibole

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jadeite, nephrite

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Origin of jade

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Formed by metamorphism of: 1, sodium-rich rocks (jadeite); or 2, dolomitic limestones mixed with shale layers (nephrite)

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most abundant minerals in the Earth’s crust. framework silicates

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feldspars

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Potassium (alkali) feldspars (“K-spars”)

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Orthoclase, moonstone, amazonite, microcline, sanidine, sunstone

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orthoclase

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From Greek, “right angle break,” referring to cleavages at 90° to each other

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amazonite

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opaque, light blue-green): From the Amazon River (first discovered in Minas Gerais, Brazil, not close to the Amazon River)

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labradorite

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(blue/green play of colors): From Labrador, where it was first found

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rubellite

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From Latin, ruber, red

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verdelite

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Probably from Spanish, verde, green

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tourmaline

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Occurs in igneous and metamorphic rocks.
Most occurs in granite pegmatites, associated with spodumene, beryl, topaz, quartz, etc

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pyrope

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(red) From Greek, pyros, fiery.

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grossularite (garnet)

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From the botanical name for gooseberry, Ribes grossularia, in allusion to its green color.

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Tsavorite (green grossular

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From Tsavo National Park, Kenya

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zoisite

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After Baron von Zois, who supplied the original specimens from Austria for description (1805)

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thulite (pink zoisite)

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After Thule, an ancient name for Norway

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anyolite (green or yellow)

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From the word for “green” in the native Masai language

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tanzanite ((blue to violet)

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After Tanzania, the source of the mine

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____ commonly occur in zoisite

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Rubies

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Blue to violet zoisite

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promoted by Tiffany & Co. beginning in 1967 under the name Tanzanite, and is today one of the most popular gems

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hematite

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Colors: Steel-gray, black, reddish-brown to red; opaque.
Streak: Red or reddish-brown.
Luster: Metallic to earthy

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sinlge refractive

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Diamond

Garnet (all types)

Spinel

Opal

Glass

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double refraction

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Zircon
Peridot or chrysolite
Tourmaline
Kunzite
Ruby and sapphire
Topaz
Amethyst and quartz topaz
Emerald and aquamarine
Chrysoberyl