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Guide To Selected Gemstones And Gem Materials Used In Jewelry

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TABLE 1-
GUIDE TO SELECTED GEMSTONES AND GEM MATERIALS USED IN JEWELRY
 
            Practical           Specific       Refractive   May be   Recognition
Name   Composition   Color   size1   Cost2   Mohs   gravity   Refraction   index   confused with   characteristics
Amber   Hydrocarbon   Yellow, red, green, blue   Any   Low to   2.0-2.5   1.0-1.1   Single   1.54   Synthetic or pressed   Fossil resin, color, low
medium plastics, kaurigum density, soft, insects.
Apatite   Chlorocalcium   Colorless, pink, yellow,   Small   Low   5.0   3.16-3.23   Double   1.63-1.65   Amblygonite, andalusite,   Crystal habit, color,
phosphate green, blue, violet brazilianite, precious hardness, appearance.
beryl, titanite, topaz,
tourmaline
Azurite   Copper carbonate   Azure, dark blue, pale   Small to   do.   3.5-4.0   3.7-3.9   do.   1.72-1.85   Dumortierite, hauynite,   Color, softness, crystal
hydroxide blue medium lapis lazuli, lazulite, habits, associated
sodalite minerals.
Benitoite   Barium titanium   Blue, purple, pink,-   do.   High   6.0-6.5   3.64-3.68   do.   1.76-1.80   Sapphire, tanzanite,   Strong blue in ultraviolet
silicate colorless blue diamond, blue light.
tourmaline, cordierite
Beryl:                                        
Aquamarine Beryllium aluminum Blue-green to light blue Any- Medium to 7.5-8.0 2.63-2.80 do. 1.58 Synthetic spinel, blue Double refraction,
silicate high topaz refractive index.
Bixbite   do.   Red   Small   Very high   7.5-8.0   2.63-2.80   do.   1.58   Pressed plastics,   Refractive index.
tourmaline
Emerald, natural   do.   Green   Medium   do.   7.5   2.63-2.80   do.   1.58   Fused emerald, glass,   Emerald filter, dichroism,
tourmaline, peridot, refractive index.
green garnet doublets
Emerald, synthetic   do.   do.   Small   High   7.5-8.0   2.63-2.80   do.   1.58   Genuine emerald   Lack of flaws, brilliant
fluorescence in
ultraviolet light.
Golden (heliodor)   do.   Yellow to golden   Any   Low to   7.5-8.0   2.63-2.80   do.   1.58   Citrine, topaz, glass,   Weak-colored.
medium doublets
Goshenite   do.   Colorless   do.   Low   7.5-8.0   2.63-2.80   do.   1.58   Quartz, glass, white   Refractive index.
sapphire, white topaz
Morganite   do.   Pink to rose   do.   do.   7.5-8.0   2.63-2.80   do.   1.58   Kunzite, tourmaline,   Do.
pink sapphire
Calcite:                                        
Marble Calcium carbonate White, pink, red, blue,- do. do. 3.0 2.72 Double 1.49-1.66 Silicates, banded agate, Translucent.
green, or brown (strong) alabaster gypsum
Mexican onyx   do.   do.   do.   do.   3.0   2.72   do.   1.60   do.   Banded, translucent.
Charoite Hydrated sodium- Lilac, violet, or white Small to do. 5.0-6.0 2.54-2.78 XX 1.55-1.56 Purple marble Color, locality.
calcium hydroxi- medium
fluoro-silicate
Chrysoberyl:                                        
Alexandrite Beryllium aluminate Green by direct sunlight, or do. High 8.5 3.50-3.84 Double 1.75 Synthetic Strong dichroism, color
incandescent light, red by- varies from red to
indirect sunlight or- green, hardness.
        fluorescent light                                
Cat-s eye do. Greenish to brownish Small to do. 8.5 3.50-3.84 do. 1.75 Synthetic, shell Density, translucence,
            large                           chatoyance.
See footnotes at end of table.
TABLE 1-Continued
GUIDE TO SELECTED GEMSTONES AND GEM MATERIALS USED IN JEWELRY
 
            Practical           Specific       Refractive   May be   Recognition
Name   Composition   Color   size1   Cost2   Mohs   gravity   Refraction   index   confused with   characteristics
Chrysoberyl:-Continued                                        
Chrysolite do. Yellow, green, and (or) Medium Medium 8.5 3.50-3.84 do. 1.75 Tourmaline, peridot Refractive index, silky.
        brown                                
Chrysocolla   Hydrated copper-   Green, blue   Any   Low   2.0-4.0   2.0-2.4   XX   1.46-1.57   Azurite, dyed   Lack of crystals, color,
silicate chalcedony, malachite, fracture, low density,
turquoise, variscite softness.-
Coral   Calcium carbonate   Orange, red, white, black,   Branching,   do.   3.5-4.0   2.6-2.7   Double   1.49-1.66   False coral   Dull translucent.
purple, or green medium
Corundum:                                        
Ruby Aluminum oxide Rose to deep purplish red Small Very high 9.0 3.95-4.10 do. 1.78 Synthetics, including Inclusions, fluorescence.
spinel, garnet
Sapphire, blue   do.   Blue   Medium   High   9.0   3.95-4.10   do.   1.78   do.   Inclusions, double
refraction, dichroism.
Sapphire, fancy   do.   Yellow, pink, colorless,-   Medium to   Medium   9.0   3.95-4.10   do.   1.78   Synthetics, glass and   Inclusions, double
orange, green, or violet large doublets, morganite refraction, refractive
index.
Sapphire or ruby,   do.   Red, pink, violet, blue, or   do.   High to low 9.0   3.95-4.10   do.   1.78   Star quartz, synthetic   Shows asterism, color
stars gray stars side view.
Sapphire or ruby,   do.   Yellow, pink, blue, green,-   Up to 20   Low   9.0   3.95-4.10   do.   1.78   Synthetic spinel, glass   Curved striae, bubble
synthetic orange, violet, or red carats inclusions.
Cubic zirconia   Zirconium and-   Colorless, pink, blue,   Small   do.   8.25-8.5   5.8   Single   2.17   Diamond, zircon,   Hardness, density, lack
yttrium oxides lavender, yellow moissanite of flaws and inclusions,-
refractive index.
Diamond   Carbon   White, blue-white,   Any   Very high   10.0   3.516-3.525   do.   2.42   Zircon, titania, cubic   High index, dispersion,
yellow, brown, green, zirconia, moissanite hardness, luster.
red, pink, blue
Feldspar:                                        
Amazonite Alkali aluminum Green-blue Large Low 6.0-6.5 2.56 XX 1.52 Jade, turquoise Cleavage, sheen, vitreous
silicate to pearly, opaque, grid.
Labradorite   do.   Gray with blue and   do.   do.   6.0-6.5   2.56   XX   1.56   do.   Do.
bronze sheen color play
(schiller)
Moonstone   do.   Colorless, white, gray,   do.   do.   6.0-6.5   2.77   XX   1.52-1.54   Glass, chalcedony, opal   Pale sheen, opalescent.
or yellow with white,
blue, or bronze schiller
Sunstone   do.   Orange, red brown,   Small to   do.   6.0-6.5   2.77   XX   1.53-1.55   Aventurine, glass   Red glittery schiller.
colorless with gold or medium
red glittery schiller
Garnet   Complex silicate   Brown, black, yellow,   do.   Low to high 6.5-7.5   3.15-4.30   Single   1.79-1.98   Synthetics, spinel,   Single refraction,
green, red, or orange - strained glass anomalous strain.
Hematite   Iron oxide   Black, black-gray,   Medium to   Low   5.5-6.5   5.12-5.28   XX   2.94-3.22   Davidite, cassiterite,   Crystal habit, streak,
brown-red large magnetite, neptunite, hardness.
                                    pyrolusite, wolframite    
See footnotes at end of table.
TABLE 1-Continued
GUIDE TO SELECTED GEMSTONES AND GEM MATERIALS USED IN JEWELRY
 
            Practical           Specific       Refractive   May be   Recognition
Name   Composition   Color   size1   Cost2   Mohs   gravity   Refraction   index   confused with   characteristics
Jade:                                        
Jadeite Complex silicate Green, yellow, black, Large Low to very 6.5-7.0 3.3-3.5 Crypto- 1.65-1.68 Nephrite, chalcedony, Luster, spectrum,
white, or mauve high crystalline onyx, bowenite, translucent to opaque.
vesuvianite,
                                    grossularite    
Nephrite Complex hydrous do. do. do. 6.0-6.5 2.96-3.10 do. 1.61-1.63 Jadeite, chalcedony, Do.
silicate onyx, bowenite,
vesuvianite,
grossularite
Jet (gagate)   Lignite   Deep black, dark brown   do.   Low   2.5-4.0   1.19-1.35   XX   1.64-1.68   Anthracite, asphalt,   Luster, color.
cannel coal, onyx,
schorl, glass, rubber
Lapis lazuli   Sodium calcium   Dark azure-blue to   do.   do.   5.0-6.0   2.50-3.0   XX   1.50   Azurite, dumortierite,   Color, crystal habit,
aluminum silicate bright indigo blue or dyed howlite, lazulite, associated minerals,
even a pale sky blue sodalite, glass luster, localities.
Malachite   Hydrated copper   Light to black-green   do.   do.   3.5-4.0   3.25-4.10   XX   1.66-1.91   Brochantite, chrysoprase, Color banding, softness,
carbonate banded opaque green associated minerals.
gemstones
Moissanite   Silicon carbide   Colorless and pale shades-   Small   Low to-   9.25   3.21   Double   2.65-2.69   Diamond, zircon, titania, Hardness, dispersion, lack
of green, blue, yellow medium cubic zirconia of flaws and inclusions,
refractive index.
Obsidian   Amorphous,   Black, gray, brown,   Large   Low   5.0-5.5   2.35-2.60   XX   1.45-1.55   Aegirine-augite,   Color, conchoidal
variable (usually dark green, white, gadolinite, gagate, fracture, flow bubbles,
felsic) transparent- hematite, pyrolusite, softness, lack of
wolframite crystal faces.
Opal   Hydrated silica   Reddish orange, colors   do.   Low to high 5.5-6.5   1.9-2.3   Single   1.45   Glass, synthetics,-   Color play (opalescence).
flash in white gray, triplets, chalcedony
black, red, or yellow
Peridot   Iron magnesium   Yellow and (or) green   Any   Medium   6.5-7.0   3.27-3.37   Double   1.65-1.69   Tourmaline, chrysoberyl   Strong double refraction,
silicate (strong) low dichroism.
Quartz:                                        
Agate Silicon dioxide Any Large Low 7.0 2.58-2.64 XX XX Glass, plastic, Mexican Cryptocrystalline,
onyx irregularly banded,
                                        dendritic inclusions.
Amethyst do. Purple do. Medium 7.0 2.65-2.66 Double 1.55 Glass, plastic, fluorite Macrocrystalline, color,
refractive index,
                                      transparent, hardness.
Aventurine do. Green, red-brown, do. Low 7.0 2.64-2.69 do. 1.54-1.55 Iridescent analcime, Macrocrystalline, color,
gold-brown, with metallic- aventurine feldspar, metallic iridescent flake
iridescent reflection emerald, aventurine reflections, hardness.
                                    glass    
See footnotes at end of table.
TABLE 1-Continued
GUIDE TO SELECTED GEMSTONES AND GEM MATERIALS USED IN JEWELRY
 
            Practical           Specific       Refractive   May be   Recognition
Name   Composition   Color   size1   Cost2   Mohs   gravity   Refraction   index   confused with   characteristics
Quartz:-Continued
Cairngorm   do.   Smoky orange or yellow   do.   do.   7.0   2.65-2.66   do.   1.55   do.   Macrocrystalline, color,
refractive index,
transparent, hardness.
Carnelian   do.   Flesh red to brown red   do.   do.   6.5-7.0   2.58-2.64   do.   1.53-1.54   Jasper   Cryptocrystalline, color,
                                        hardness.
Chalcedony   do.   Bluish, white, gray   do.   do.   6.5-7.0   2.58-2.64   do.   1.53-1.54   Tanzanite   Do.
Chrysoprase do. Green, apple-green do. do. 6.5-7.0 2.58-2.64 do. 1.53-1.54 Chrome chalcedony, Do.
jade, prase opal,
prehnite, smithsonite,
variscite, artificially
colored green
                                    chalcedony    
Citrine do. Yellow do. do. 7.0 2.65-2.66 do. 1.55 do. Macrocrystalline, color,
refractive index,
                                        transparent, hardness.
Jasper do. Any, striped, spotted, or do. do. 7.0 2.58-2.66 XX XX do. Cryptocrystalline,
sometimes uniform opaque, vitreous luster,
                                        hardness.
Onyx do. Many colors do. do. 7.0 2.58-2.64 XX XX do. Cryptocrystalline,
uniformly banded,
                                        hardness.
Petrified wood   do.   Brown, gray, red, yellow   do.   do.   6.5-7.0   2.58-2.91   Double   1.54   Agate, jasper   Color, hardness, wood
                                        grain.
Rock crystal do. Colorless do. do. 7.0 2.65-2.66 do. 1.55 Topaz, colorless Do.
                                    sapphire    
Rose do. Pink, rose red do. do. 7.0 2.65-2.66 do. 1.55 do. Macrocrystalline, color,
refractive index,
                                        transparent, hardness.
Tiger-s eye do. Golden yellow, brown, do. do. 6.5-7.0 2.58-2.64 XX 1.53-1.54 XX Macrocrystalline, color,
        red, blue-black                               hardness, chatoyancy.
Rhodochrosite   Manganese carbonate   Rose-red to yellowish,   do.   Low   4.0   3.45-3.7   Double   1.6-1.82   Fire opal, rhodonite,   Color, crystal habit,
stripped tugtupite, tourmaline reaction to acid, perfect
                                        rhombohedral cleavage.
Rhodonite Manganese iron Dark red, flesh red, with do. do. 5.5-6.5 3.40-3.74 do. 1.72-1.75 Rhodochrosite, thulite, Color, black inclusions,
calcium silicate dendritic inclusions of hessonite, spinel, lack of reaction to acid,
black manganese oxide pyroxmangite, hardness.
                                    spessartine, tourmaline    
Shell:
Mother-of-pearl Calcium carbonate White, cream, green, Small do. 3.5 2.6-2.85 XX XX Glass and plastic Luster, iridescent play
blue-green, with imitation of color.
        iridescent play of color                                
See footnotes at end of table.
TABLE 1-Continued
GUIDE TO SELECTED GEMSTONES AND GEM MATERIALS USED IN JEWELRY
 
            Practical           Specific       Refractive   May be   Recognition
Name   Composition   Color   size1   Cost2   Mohs   gravity   Refraction   index   confused with   characteristics
Shell:-Continued
Pearl do. White, cream to black, do. Low to high 2.5-4.5 2.6-2.85 XX XX Cultured and glass or- Luster, iridescence,
sometimes with hint of plastic imitation x-ray of internal structure.
        pink, green, purple                                
Spinel, natural Magnesium Any Small to Medium 8.0 3.5-3.7 Single 1.72 Synthetic, garnet Refractive index, single
    aluminum oxide       medium                           refraction, inclusions.
Spinel, synthetic do. do. Up to 40 Low 8.0 3.5-3.7 Double 1.73 Spinel, corundum, beryl, Weak double refraction,
            carats                       topaz, alexandrite   curved striae, bubbles.
Spodumene:
Hiddenite Lithium aluminum Yellow to green Medium Medium 6.5-7.0 3.13-3.20 do. 1.66 Synthetic spinel Refractive index, color,
    silicate                                   pleochroism.
Kunzite do. Pink to lilac do. do. 6.5-7.0 3.13-3.20 do. 1.66 Amethyst, morganite Do.
Tanzanite   Complex silicate   Blue to lavender   Small   High   6.0-7.0   3.30   do.   1.69   Sapphire, synthetics   Strong trichroism, color.
Topaz do. White, blue, green, pink, Medium Low to 8.0 3.4-3.6 do. 1.62 Beryl, quartz Color, density, hardness,
yellow, gold medium refractive index, perfect
                                        in basal cleavage.
Tourmaline do. Any, including mixed do. do. 7.0-7.5 2.98-3.20 do. 1.63 Peridot, beryl, garnet Double refraction, color,
                                    corundum, glass   refractive index.
Turquoise Copper aluminum Blue to green with black, Large Low 6.0 2.60-2.83 do. 1.63 Chrysocolla, dyed Difficult if matrix not
phosphate brown-red inclusions howlite, dumortierite, present, matrix usually
                                    glass, plastics, variscite   limonitic.
Unakite Granitic rock, Olive green, pink, do. do. 6.0-7.0 2.60-3.20 XX XX XX Olive green, pink, gray-
feldspar, epidote, and blue-gray blue colors.
    quartz                                    
Zircon Zirconium silicate White, blue, brown, yellow, Small to Low to 6.0-7.5 4.0-4.8 Double 1.79-1.98 Diamond, synthetics, Double refraction,
or green medium medium (strong) topaz, aquamarine strongly dichroic, wear
                                        on facet edges.
Do., do. Ditto. XX Not applicable.
1Small, up to 5 carats; medium, 5 to 50 carats; large, more than 50 carats.
2Low, up to $25 per carat; medium, up to $200 per carat; high, more than $200 per carat.

Source: United States Geological Survey Mineral Resources Program

See also: Mineral commodity prices

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