Gemstone

Cut Gemstones
Credit: Alvonzo Zone

Description

Polished gemstones
Credit: Adrian Pingstone

An ornamental, often valuable, mineral used for decoration in jewelry, small objects and clothing. Gems are found in alluvial deposits and dug from veins. Major mining locations include Sri Lanka, southeast Asia, South Africa, Australia, Russia, Brazil and Colombia. Gemstones are characterized based on their color, clarity, cut and weight. Stones of exceptional size, beauty or rarity are highly valued. Techniques for cutting and polishing gemstones were developed in India in the 14th century. Gemstones can usually be classified into three types:

• Transparent crystalline stones; usually cut: Amethyst, Aquamarine, Citrine, Emerald, Diamonds, Garnets, Peridot, Quartz, Rubies, Sapphires, Spinel, Tanzanite, Topaz, Tourmaline, and Zircon.
• Non-transparent minerals, usually polished: Agate, Carnelian, Cat's eye, Chrysoberyl, Chrysocolla, Jasper, Lapis lazuli, and Turquoise
• Non-stone materials: Ivory, Amber, Jet, and Coral

Gemstone facet cuts

Properties of Common Gemstones

Mineral		Gem		Color		Mohs hardness		Specific gravity		Refractive index		Crystal system		Other		Fluorescence		Dispersion		Inclusions
beryl		aquamarine		sky blue		7.5-8.0		2.68-2.71		epsilon = 1.570-1.580 omega = 1.574-1.586		hexagonal crystal system; conchoidal fracture		transparent; weakly pleochroic		none to weak; synthetic stones may appear opaque and dull red in longwave UV				Aquamarines are often flawless; Other contain many inclusions such as mica, pyrite and calcite
		goshenite		colorless
		heliodor		yellow
		emerald		green				2.68-2.78		epsilon = 1.571-1.581 omega = 1.577-1.588
		morganite		pink				2.66-2.83		epsilon = 1.580-1.590 omega = 1.589-1.601
chrysoberyl		alexandrite		green in daylight, red in incandescent light		8.5		3.5-3.8		alpha = 1.745 beta = 1.748 gamma = 1.754		orthorhombic, flattened crystals, often twinned		transparent; chrysoberyl cat's-eye is chatoyant		strongly pleochroic		d = 0.015
cristobalite		opal		milky white to colorless;; variable pale shades		5.5-6.5		1.98-2.25		1.435-1.455		tetragonal submicrocrystalline aggregates; irregular concretions; glass- like fracture		opaque; contains some water causing the physical properties to vary		may fluoresce white or pale green; may phosphoresce				possible
corundum		sapphire		blue		9.0		4.0		epsilon = 1.757-1.768 omega = 1.765-1.776		hexagonal; conchoidal fracture		transparent; marked dichroism		orange to red; heat treated stones may fluoresce green		d = 0.018		many including minerals (rutile), fluids, angular banding
		ruby		red
		padmaradschah		orange
diamond		diamond		variable (colorless, yellow, blue)		10.0		3.52		2.4175		isometric flattened octahedrons; dodecahedrons		transparent; perfect cleavage in four directions		may fluoresce pale colors in longwave UV; may phosphoresce		d = 0.044		trigonal on surface; numerous inclusions
potash feldspar		orthoclase		pale yellow to flesh red		6.0-6.5		2.6		alpha = 1.518 beta = 1.522 gamma = 1.522		monoclinic crystals		two perfect cleavages at right angles
		moonstone		colorless, white to yellowish								nodules or masses		blue opalecsence
		amazonite		yellow green to blue green								triclinic, large crystals		variety of microcline
plagioclase feldspar		sunstone (aventurine)		colorless to pale pink		6.0-6.5		2.6-2.7		alpha = 1.527-1.577 beta=1.531-1.585 gamma = 1.538-1.590		triclinic prismatic crystals; two perfect cleavages at right angles		transparent to opaque; iridescent;						inclusions give spangled appearance
		labradorite		grayish shades
fluorite		fluorite		lavender to green						1.434		conchoidal fracture		transparent		strong				color zoning
garnet		almandine (carbuncle)		deep red with a trace of purple		7.0-7.5		4.3		1.79-1.83		isometric euhedral crystals, with dodecahedrons and trapezodrons most common; conchoidal fracture		light colored varieties are transparent; no birefringence, no pleochroism		none		d = 0.024		needles; single and multiphase prisms
		andradite (Uralian emerald)		deep emerald-green		6.5-7.0		3.9		1.887						none		d = 0.057
		grossularite (hessonite)		yellow-brown to orange, red, or green		7.0-7.5		3.6		1.734-1.740						pale orange in long UV; yellow in short UV		d = 0.028
		pyrope		dark blood red		7.0-7.5		3.78		1.714-1.742						none		d = 0.027
		spessartine		yellow-orange to brown- red		7.0-7.5		4.15		1.800-1.810						none		d = 0.027
jade		jadeite (Imperial jade)		green but may be white, black, red, brown, yellow, blue or mauve		6.0		3.33-3.34		alpha = 1.640-1.658 beta=1.645-1.663 gamma = 1.652-1.673		monoclinic compact or fibrous masses; granular to splintery fracture		translucent to opaque; greasy luster		may have pale white color in long UV light
		nephrite		deep spinach green to near-white		6.0-6.5		2.96-3.02		alpha = 1.600-1.672 beta=1.614-1.686 gamma = 1.627-1.693		monoclinic compact masses; conchoidal to granular fracture		translucent to opaque; greasy or waxy appearance		none				some dark inclusions
lazurite		lapis lazuli		azure blue with flecks of white and gold		5.0-5.5		2.7-2.9		1.50-1.67		isometric with compact masses; opaque		decomposed by hydrochloric acid
olivine		peridot; chrysolite		yellow green; dark bottle green; olive green		6.5-7.0		3.3-3.4		alpha = 1.635-1.671 beta = 1.652-1.698 gamma = 1.671-1.707		orthorhombic system with massive or granular forms; fracture=uneven to conchoidal		transparent				d = 0.020
quartz		amethyst		purple		7.0		2.65		epsilon = 1.553 omega = 1.544		conchoidal fracture		transparent; heat treatment may bleach stones				d = 0.013
		cairngorm (smoky quartz)		smoky brown
		citrine		yellow
		rock crystal		colorless
		rose quartz		pink
		agate (moss agate, mocha stone)		variable								compact masses; nodules		translucent to opaque
		chalcedony (onyx, carnelian, sardonyx, chrysoprase, bloodstone, heliotrope)		variable
		jasper		variable
spinel		Balas ruby;		typically red; also variable: yellow (rubicelle), violet (almandine), pleonast (blue, black), gahnite (blue-green)		8		3.6		1.715-1.725		isometric octahedral crystals; rounded grains; conchoidal fracture		transparent		natural fluoresces red in longwave UV; synthetic may show colors in shortwave UV		d = 0.020		fingerprint pattern inclusions
topaz		topaz, hyacinth		yellow, green, blue, violet or red		8		3.4-3.6		alpha = 1.606-1.629 beta = .609-1.631 gamma = 1.616-1.638		orthorhombic prismatic crystals; perfect cleavage in one direction		transparent; highly pleochroic; turns soft red when heated		may fluoresce yellow in longwave UV		d = 0.014		single and multiphase
tourmaline		achroite		colorless or green		7-7.5		2.9-3.2		epsilon = 1.610-1.650 omega = 1.635-1.675		hexagonal prismatic crystals, often rounded or oval; conchoidal fracture		transparent; pleochroic		none to weak		d = 0.016		gas and liquid pockets with color zoning
		dravite		brown
		indicolite		blue
		rubellite		pink
		schorl		black
		siberite		violet
turquoise		turquoise		blue to greenish-blue		5.0-6.0		2.6-2.9		alpha = 1.61 beta = 1.62 gamma = 1.65		cryptocrystalline to fine granular; fracture=conchoidal		opaque; color fades in sunlight
zircon		jargon		variable		6.0-7.5		4.6-4.7		epsilon = 1.968-2.015 omega = 1.923-1.960		tetragonal system with square prismatic crystals; fracture=uneven		transparent; pleochroic		some show dull yellow color; some may phosphoresce		d = 0.048		rutile crystals; single and multiphase
		Matura diamond		colorless
		hyacinth		yellow orange
		jacinth		red brown

Synonyms and Related Terms

gemstones; gem; gem; ædelsten (Dan.); Schmucksteine (Deut.); gema (Esp.); gemme (Fr.); edelsteen (Ned.); gema (Port.); Ädelsten (Sven.)

For easy print or to download

Properties of Common Gemstones

Natural and Simulated Diamonds

Resources and Citations

• Encyclopedia Britannica, http://www.britannica.com Comment: "gemstone." Accessed 10 Nov. 2004 .
• C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979
• The Dictionary of Art, Grove's Dictionaries Inc., New York, 1996 Comment: Gems: cutting. by Ken Scaratt
• Wikipedia: http://en.wikipedia.org/wiki/Gemstone (Accessed Nov. 2, 2005)