REVIEW NOTES

VARIETAL NAMES

Know the following varietal names and the color or other features they denote. For major varieties, know the common chromophore or coloring agent.

Quartz: Rock Crystal, Rose (Ti), Amethyst (Fe), Citrine (Fe), Smokey (color center), Milky (fluid inclusions), Aventurine (muscovite inclusions), Tiger eye (replacing asbestos; Fe-oxide).

Chalcedony: Carnelian (red; Fe), Sard (brown; Fe), Chrysoprase (apple green; Ni), Agate, Onyx, Jasper (red; Fe), chert, flint, bloodstone (green with red spots; Fe).

Beryl: Emerald (Cr), Green, Aquamarine (Fe), Golden Beryl (Fe), Morganite (Mn; pink), Heliodor (Fe; yellow).

Tourmaline: Indicolite (or blue; Fe), Rubellite (or pink; Fe), Chrome Tourmaline (Cr; Green), Watermelon, Bicolored, Parti-colored.

Topaz: Imperial (brown-orange), Blue; both by color centers.

Opal: Black, White, Jelly ("water"), Cherry, Pinfire, Mosaic, Flame. Play of color caused by diffraction.

Peridot : (yellow-green; Fe).

Jade: Nephrite, Jadeite (Cr, Fe), Imperial.

Garnet: Grossular (var. Tsavorite is green; Hessonite is brownish-yellow), Pyrope (red; Fe), Almandine (red; Fe), Spessartine (orange; Mn), Rhodolite (violet red; Fe), Demantoid (green; Fe).

Spinel: Red (Cr), Blue (Fe), Pink (Cr), Purple, Orange, Black.

Turquoise (Cu): Persian, Spiderweb, Matrix.

Lapis Lazuli: "German Lapis", "Swiss Lapis" (=dyed Chalcedony).

Corundum: Ruby (Cr + Fe), Sapphire (Fe, Ti), Padparadscha (pinkish orange)

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CHEMICAL FORMULAE

I don't expect you to memorize the chemical formulae for the gems we've covered, however, you should know the important elements in each. They are as follows (underlined elements are unique to the gem):

  • Quartz - Si
  • Chalcedony - Cryptocrystalline Quartz
  • Beryl - Be, Al, Si
  • Tourmaline - B, Al, Si (also one or more Fe, Mg, Na, K, Li)
  • Corundum - Al
  • Topaz - F, Al, Si
  • Opal - Si, H2O
  • Diamond - C
  • Peridot - Fe, Mg, Si
  • Zircon - Zr, Si
  • Garnet - Fe, Mg, Ca, Mn, Al, Si
  • Spinel - Al, Mg
  • Turquoise - Cu, P
  • Lapis (lazurite)- Na, Al, S, Si

There are four broad categories of minerals here: Silicates (those containing Si), Oxides (Corundum, Spinel), Phosphates (Turquois), and native elements (Diamond).

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IMPORTANT TREATMENTS
(a more complete list is here)

Heating Irradiation Dying Oiling
  • Amethyst
    (to Citrine)
  • Sapphire
    (pink to padpar.)
  • Chalcedony
  • Emerald
  • Smokey Qtz
    (to Rock Crystal or Citrine)
  • Topaz
    (+/- heat for blue)
  • Turquoise
  • Ruby(?)
  • Sapphire
    (lighten or darken,
    change color, improve clarity)
  • Pearls
    (cultured white
    to black)
  • Pearls
  • Ruby
    (improve color)
  • Tourmaline
    (pink to red, bicolors)
  • Lapis
  • Aquamarine
    (improve color)
  • Jade
  • Tourmaline
    (improve color)

  • Topaz
    (+/- irradiation for blue)

  • Zircon
    (change color)

Other Treatments

  • Diffusion (Sapphire, Star Sapphire)

  • Backings & Coatings (Diamond, Opal)

  • Lasering (Diamond)

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SOURCES OF ORIGIN
(Italic denote major production)

A. Southeast Asia (primarily gem gravels)

1) Myanmar (ne Burma) - Corundum, Peridot, Jade, Spinel, Zircon

2) Thailand - Corundum, Spinel, Zircon

3) Sri Lanka - Corundum, Spinel, Topaz, Garnet, Tourmaline, Zircon, Pearls

B. Middle East

1) Iran - Turquoise

2) Afghanistan - Lapis

3) Egypt - Peridot (Red Sea; isle of St. John)

4) Persian Gulf - Pearls

C. Former Soviet Union

1) Ural Mts.- Amethyst, Demantoid

2) Other Areas - Lapis, Diamond

D. South America

1) Brazil - mostly from the state of Minas Gerias, in pegmatites and placers.

  • Amethyst, Rock Crystal, Rose Quartz, Agate, Beryl (including emerald), Topaz, Tourmaline, Diamond

2) Colombia - two famous Emerald localities; Muzo and Chivor

3) Chile - Lapis

E. Africa

1) South Africa - Diamond, Tiger eye, Pyrope

2) Zimbabwe - Emerald, Diamond

3) Zambia -Emerald

4) Kenya, Tanzania - Tsavorite, Chrome Tourmaline, Rhodolite, Malaia Garnet

F. North America

1) U.S. - Nephrite (Wyoming), Opal (Nevada), Corundum (Montana), Turquoise (southwest), Rock Crystal (Arkansas), Peridot (Arizona), Tourmaline (Maine and southern California).

2) Mexico - Opal (cherry, fire, jelly, little black), Chalcedony of all kinds, Topaz.

G. Australia

Opal (black from Mintabie and Lightning Ridge; white mostly from Coober Pedy), Sapphire, Diamond.

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DISTINGUISHING AMONG SIMILAR APPEARING GEMS

  • RED STONES: Spinel vs. Ruby vs. Garnet
    • Anisotropic vs. isotropic (S vs. R or G), u.v. fluorescence and inclusions (S vs. G)
    • Ruby dichroic, spinel and garnet aren't.
  • BLUE STONES: Topaz vs. Sapphire vs. Aquamarine vs. Spinel vs. Zircon
    • Spinel isotropic
    • Zircon R.I. is 1.9 -1.94 (off scale), v. high S.G.- 4.7
    • Aquamarine R.I.=1.57-1.58; Topaz R.I=1.61-1.64; Sapphire R.I.=1.76-1.77
  • GREEN STONES: Tourmaline vs. Peridot vs. Emerald vs. Tsavorite
    • Tsavorite isotropic
    • Tourmaline v. strongly pleochroic
    • Peridot R.I.=1.65, Emerald R.I. = 1.57-1.58, colors usually quite different (more yellow in peridot)

 

  • PINK STONES: Tourmaline vs. Spinel vs. Sapphire vs. Morganite
    • Spinel isotropic
    • Tourmaline much more pleochroic than others
    • Sapphire R.I=1.76-1.77, Morganite=1.57-1.58

 

  • YELLOW STONES: Heliodor vs. Citrine vs. Topaz
    • Citrine R.I.=1.54-1.55; Heliodor R.I.=1.57-1.58; Topaz R.I.=1.61-1.6

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Notes Index | Corundum | Beryl | Diamond | Pearl | Opal | Jade | Topaz | Tourmaline
Peridot | Garnet | Zircon | Spinel | Quartz | Metals | References | Review Notes | Home

©1998
Updated 08/20/09
Comments and questions to helper@mail.utexas.edu
Department of Geological Sciences
The University of Texas at Austin