Introduction Gemstone:
A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, and jade) or organic materials that are not minerals (such as amber, jet, and pearl) are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.
Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter; a diamond worker is a diamantaire.
For centuries, artists and poets have used images of colored stones to express love, passion, and power. People in every era and from all walks of life have adorned themselves with the dramatic, radiant grace of colored stone jewelry. Here are refer to some types of precious stones:
A G A T
Chalcedony
Agate is a fine-grained chalcedony quartz and one of the first gem materials known. Its history goes all the way back to the ancient Egyptians, who first used it for adornment more than 3,000 years ago. Ancient cultures used it in amulets and talismans.
They believed that it provided the wearer with a bold heart and pleasant dreams. Roman artisans carved seals from it. Nineteenth century Victorians used it to create beautiful cameos. The characteristic that sets agate apart from other chalcedonies is its appearance: It boasts dramatic curved or angular stripes, or bands of color. These distinctive markings vary widely in color and translucence.
The patterns in some agates look like moss, ferns, and trees even entire landscapes. Others have simple striped patterns of two or more colors. Besides cameos, modern cutting styles that make the most of agate’s unique appearance include cabochons, beads, and carvings. Fire agate is a relative newcomer to the agate family, discovered in the 1940s. Its mineral layers cause light interference and give it a shimmering iridescence against its brown bodycolor.
Sources: Brazil Hardness & Toughness:
India
Madagascar Hardness 61/2to 7 on Mohs scale
Mexico Toughness Good
United States
Uruguay
Varieties
Eye agate, orbicular agate
Banded in concentric rings
Landscape agate
Chalcedony with colored patterns resembling a landscape
Fire agate
Iridescent inner layers
Dendritic agate, scenic agate
Colorless or white, translucent, with markings resembling trees, ferns, moss, or landscapes
Iris agate
Semitransparent to translucent, with iridescent colors
Ronded agatRonded agat
Fire agate
Dendritic agate
Stability
Environmental Factor Reaction
Heat Color may change
Light Stable
Chemicals Attacked by hydrofluoric acid; nitric acid may attack dye
Treatments
Treatment Dyeing
Description
Gray south American agate is dyed with inorganic dye. Layers absorb dye differently depending on porosity.
Purpose: improves banding
Stability:
Generaly stable under normal conditions. May fade or be removed by chemicals.
Prevalence: common
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Heating |
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orange or orangy red color in yellow to brown agate |
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Improves color |
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Permanent |
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common |
Care and Cleaning: | |
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Advisability |
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Not recommended |
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Not recommended |
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Safe |
Alexandrite
Alexandrite/Chrysoberyl
Alexandrite is a rare chrysoberyl variety with chameleon-like qualities. Its color is a lovely green in daylight or fluorescent light, but it changes to brownish or purplish red in the incandescent light from a lamp or candle flame. Alexandrite’s dramatic color change is sometimes described as “emerald by day, ruby by night.” Other gems also change color in response to a change in light source, but this gem’s transformation is so striking that the phenomenon itself is often called “the alexandrite effect.” Abundant alexandrite deposits were first discovered in 1830, in Russia’s Ural Mountains. Those first alexandrites were of very fine quality, and displayed vivid hues and dramatic color changes. The gem was named after the young Czar Alexander II, and it caught the country’s attention because its red and green colors mirrored the Imperial Russian flag. The spectacular Ural Mountain deposits didn’t last forever, and now most alexandrite comes from Sri Lanka, East Africa, and Brazil. The newer deposits contain some fine-quality stones, but many possess less precise color change and muddier hues than the nineteenth century Russian alexandrites. You’ll still find some of the famed Ural Mountain alexandrites in estate jewelry. They remain the quality standard for this phenomenal gemstone. Because of its scarcity, especially in larger sizes, alexandrite is a relatively expensive member of the chrysoberyl family. It shares its designation as a June birthstone with cultured pearl and moonstone.
Sources:
Brazil
East Africa
Russia
Sri Lanka
Hardness & Toughness:
Hardness 81/2on Mohs scale
Toughness Excellent
Stability:
Environmental Factor Reaction
Heat Stable
Light Stable
Chemicals None
Care and Cleaning:
Type of Cleaning Advisability
Ultrasonic cleaning Usually safe
Steam cleaning Usually safe
Warm, soapy water Safe
Imitations:
Synthetic color-change sapphire
Synthetic color-change spinel
Alternatives:
Color-change garnet
Color-change sapphire
Alexandrites in incandescent light
Alexandrites in fluorescent light
Almandite
Almandite/Garnet
Almandite is probably one of the most familiar of the closely related species that make up the garnet group. It’s a fairly common red garnet, with a color range from orangy red through red to reddish purple. Almandite was named for Alabanda, an ancient Asian town and an active gemstone trading and fashioning center. Ancient Romans often fashioned almandite garnets as thin, hollowed cabochons to bring out the intensity of their color. Other species in the garnet group come in a variety of hues, from browns and oranges to vibrant greens. As far back as 3100 BC, Egyptians along the Nile worked garnet into beads and inlays. Noah is said to have recognized garnet’s inner fire and used it as a lamp on the bow of the ark. Garnets of all species, including almandite, are considered January birthstones.
Sources:
Brazil
Ina
Madagascar
Pakistan
Sri Lankadi
United States
Hardness & Toughness:
Hardness 7 to 71/2on Mohs scale
Toughness Fair to good
Care and Cleaning:
Type of Cleaning Advisability
Ultrasonic cleaning Usually safe
Steam cleaning Never
Warm, soapy water Safe
Stability:
Environmental Factor Reaction
Heat Abrupt temperature changes likely to cause fracturing
Light Stable
Chemicals None, except concentrated hydrofluoric acid
Imitations:
Garnet-and-glass doublet
Alternatives:
Hessonite garnet
Malaya garnet
Pyrope garnet
Rhodolite garnet
Ruby
Spessartite garnet
Spinel
Tourmaline
Amber
Amber belongs to the category of organic gems—the products of living organisms and biological processes. Amber formed millions of years ago, when sap from ancient trees hardened and fossilized. Stone Age people discovered these golden jewels along the shores of the Baltic Sea, and they became perhaps the earliest and most consistently popular ornamental gems. Scientists and collectors treasure amber that contains suspended animal or plant fragments: Fossilized bits of once-living things that were trapped in the hardening amber millions of years ago, creating a fascinating time capsule. Some types of amber are found in the ground. Other types have been freed and carried by tides and end up on beaches or near-shore areas. The Baltic coast bordering Germany, Poland, and Russia is still a source of amber, which is sometimes called “gold of the North.” Amber’s warm luster is featured in beads, carvings, pendants, and cabochon rings, as well as decorative items like cups, bowls, snuff boxes, and umbrella handles. Amber’s colors range from whites, yellows, and oranges to reds and browns. Clear material is preferred in the US, cloudy in Europe and North Africa. Heating cloudy amber in oil clarifies it. Heat treatment can also produce disk-like stress fractures and create an attractive product called sun-spangled amber.
Sources:
Dominican Currently the major source
Republic
Germany
Mexico
Poland
Russia
Hardness & Toughness:
Hardness: 2 to 21/2on Mohs scale
Toughness: Poor
Stability:
Environmental Factor Reaction
Heat Burns at low temperatures
Light May darken with age
Chemicals Attacked by acids, caustics, alcohol, gasoline
Treatments:
Treatment Purpose Stability Prevalence Detection
Heating in oil clarifies cloudy amber Stable Occasional May be detectable
Heating Lightens color Stable Occasional Undetectable
Heating(some times wit oil) produces sum spangles Stable Common May be detectable
Dyeing Darkens color May fade Occasional May be detectable
Care and Cleaning:
Type of Cleaning Advisability
Steam cleaning Never
Ultrasonic cleaning Never
Warm, soapy water Safe, but hard brushes may scratch
Imitations:
Ambroid (reconstructed or pressed amber)
Copal (a natural resin, younger than amber)
Plastic
Yellow glass
Amethyst
Amethyst/Quartz
Amethyst has been the most prized member of the quartz family for centuries. Early Greek legends, and its wine-purple color, associated amethyst with Bacchus, the god of wine. Other legends led to beliefs that amethyst gems kept their wearers clear-headed and quick-witted in battle and in their business affairs. It’s no wonder that fine amethyst adorns the fingers of bishops and the coronation regalia of British royalty. Russia was once the main source of amethyst, but near the turn of the twentieth century, new deposits were discovered in South America. After that, it became more widely available, but no less treasured. Amethyst comes in a range of sizes, and the color selection ranges from palest lilac to rich purple. Experts consider African amethyst’s royal purple with reddish overtones to be the gem’s finest color. Aclosely related quartz variety called ametrine contains a striking mixture of two contrasting quartzes purple amethyst and yellow citrine. Ametrine deposits are found in Brazil and Bolivia. Amethyst is the birthstone for February.
Sources:
Brazil Major source
India
Namibia
Sri Lanka
United States
Uruguay
Zambia
Hardness & Toughness:
Hardness 7 on Mohs scale
Toughness Good
Care and Cleaning:
Type of Cleaning Advisability
Steam cleaning Not recommended
Ultrasonic cleaning Usually safe
Warm, soapy water Safe
Stability:
Environmental Factor Reaction
Heat Abrupt temperature change may fracture stone, can alter color
Light Some amethyst may fade
Chemicals Damaged by hydrofluoric acid, ammonium fluoride, alkalies
Treatments:
Treatment Heating
Purpose lightnes color or produces citrine or green quartz
Stability Excellent
Prevalence Occasional
Detection Undetectable
Synthetics:
Hydrothermal
Alternatives:
Iolite
Rhodolite
garnet
Sapphire
Spinel
Tanzanite
Topaz
Tourmaline
Aquamarine
Aquamarine/Beryl
Aquamarine’s cool blue hues are reflected in its name, which comes from the Latin for “sea water.” Medieval sages prescribed water touched by aquamarine for a host of ills, including those affecting the eyes and lungs. They promised the virtues of insight and foresight to the gem’s wearers. Aquamarine crystals can grow to huge sizes, and are usually blessed with excellent clarity. Gem bodycolors range from greenish blue to blue-green in light tones. Usually, the color is more intense in larger stones, but some aquamarine from Africa displays deeper blues in faceted stones of less than 5 cts. Brazil supplies the most aquamarine to the modern market. Like emerald, aquamarine is a member of the beryl species. The gem is March’s birthstone.
Sources:
Australia
Brazil Major source
China
Kenya
Madagascar
Mozambique
Nigeria Known fes (unor intense color in smaller sizder 5 cts.)
Pakistan
United States
Zambia
Hardness & Toughness:
Hardness 71/2to 8 on Mohs scale
Toughness Good
Stability:
Environmental Factor Reaction
Heat Exposure to heat not recommended
Light Stable
Chemicals Attacked by hydrofluoric acid
Treatments:
Treatment Heating
Purpose removes yellow,resulting in purer blue color
Stability very good
Prevalence Routine
Detection Undetectable
Care and Cleaning:
Type of Cleaning Advisability
Ultrasonic cleaning
Usually safe, unless stone contains feathers or liquid inclusions
Steam cleaning
Usually safe, unless stone contains feathers or liquid inclusions
Warm, soapy water Safe
Imitations:
Glass
Synthetic spinel
Alternatives:
Blue topaz
Sapphire
Spinel
Tanzanite
Tourmaline
Cat’s-Eye
Cat’s-Eye/Chrysoberyl
This gem, with its band of reflected light across the middle, has always reminded observers of the eye of a cat. The cat’s-eye effect, also called chatoyancy, is caused by parallel needle-like inclusions within the stone. The gem was once known as cymophane-Greek for “waving light.” In some cultures, its distinctive appearance made it the preferred treatment for all sorts of eye ailments. Chatoyancy appears in other gemstones, but fine-quality cat’s-eye chrysoberyl sets the standard. It’s also the most valuable cat’s-eye stone. It’s durable as well as attractive, which makes it popular in men’s rings, cufflinks, and tie tacks. The cabochon cut brings out its cat’s-eye effect to best advantage. Cat’s-eye chrysoberyl ranges from brown to greenish yellow. The finest quality specimens boast a golden color, with bands that span the entire length of the gem. The bands themselves are distinct, silvery-white, and straight. The chatoyant band in cat’s-eyes will appear to blink when you hold the stone between two light sources, then rotate it. As you turn the stone, the eye splits into two bands that move apart, then back together. This effect is called “opening and closing.” Cat’s-eyes display another impressive effect, called milk and honey. With the light positioned perpendicular to the chatoyant band, the side nearest the light shows the stone’s original bodycolor while the other side has a milky appearance.
Sources:
Brazil
East Africa
Sri Lanka
Hardness & Toughness:
Hardness 81/2on Mohs scale
Toughness Excellent to good
Stability:
Environmental Factor Reaction
Heat Stable
Light Stable
Chemicals None
Care and Cleaning:
Type of Cleaning Advisability
Ultrasonic cleaning Usually safe
Steam cleaning Usually safe
Warm, soapy water Safe
Imitations:
Cat’s-eye glass
Alternatives:
Cat’s-eye quartz
Cat’s-eye tourmaline
Tiger’s-eye quartz
Citrine
Citrine/Quartz
Citrine is one of the US birthstones for November (the other is topaz). It’s a quartz variety, and the top-selling transparent gem in the yellow to orange color range. Its name was derived from the Latin word citrus, meaning “citron” (a fruit closely related to the lemon). This gem combines a warm, attractive color with good wearability and a moderate price—an unbeatable combination for many customers. Citrine comes in an exceptionally wide range of sizes. The largest transparent faceted gem on record (in terms of dimensions and volume) is a citrine. It measures 25.5 cm ˘ 14.1 cm ˘ 10.0 cm (9.9 in. ˘ 5.5 in. ˘ 3.9 in.), and weighs 19,548 cts. (3.9 kg/8.6 lb.). Jewelry-sized citrines are readily available in weights of up to 20 cts. and more. Most citrine is faceted in traditional rounds and fancy shapes, but you’ll also find it fashioned into more unusual cuts and carvings. Leading jewelry designers use citrine alone, in combination with diamonds, and in multicolored creations alongside gems with contrasting colors— amethyst, aquamarine, blue topaz, and others. Before the development of modern gemology, citrine was traditionally confused with topaz because of their similar colors.
Sources:
Bolivia
Brazil
Spain
Hardness & Toughness:
Hardness 7 on Mohs scale
Toughness Good
Stability:
Environmental Factor Reaction
Heat
High heat can cause color loss; sudden or extreme temperature change can cause fracturing
Light Stable
Chemicals
Soluble in hydrofluoric acid and ammonium fluoride; very slightly soluble in alkalis
Treatments:
Treatment Heating
Purpose Produces color changes amethyst to citrine
Stability Permanent under normal conditions
Prevalence Routine most citrine is produced by heat treating amethyst.
Detection Undetectable Treatment is assumed.
Care and Cleaning:
Type of Cleaning Advisability
Ultrasonic cleaning Usually safe
Steam cleaning Not recommended
Warm, soapy water Safe
Imitations: Amber
Glass Carnelian
Plastic Chrysoberyl
Synthetic hydrothermal quartz Malaya garnet
Synthetic sapphire Sapphire
Synthetic spinel Smoky quartz
Spessartite garnet
Topaz
Tourmaline
Demantoid
Demantoid/Andradite/Garnet
Demantoid means “diamond-like” in Dutch, the language of Renaissance diamond cutters. Its name reflects the fact that, while demantoid is much softer than diamond, its dispersion is higher, so its flashes of rainbow color are very noticeable, especially in lighter-colored stones. This lush green gem is a variety of andradite and a member of the garnet group. Demantoid displays intense color in the green to yellow-green range. Under the microscope, fine demantoid has another telltale signature: Its classic “horse-tails.” They are wisps of long, golden, fiber-like inclusions that radiate from a central point. Demantoid was discovered in Russia’s gem-rich Ural Mountains in 1868. Tiffany and Company’s chief gem buyer, George Kunz, fell in love with the newly discovered gem, and the company bought up all that they could get. Tiffany marketed it as an appealing emerald alternative. Even though it was rarely available in sizes larger than 2 cts., demantoid adorned much Victorian jewelry crafted between 1895 and 1915. The historic Russian source doesn’t yield much demantoid any more. In fact, the scarcity of fine-quality demantoid has made it a prized collector’s stone. Recent discoveries in Namibia, however, have increased the availability. Demantoid joins the rest of the garnet group as a January birthstone.
Sources:
Namibia
Russia
Zaire
Hardness & Toughness:
Hardness 61/2to 7 on Mohs scale
Toughness Fair to good
Stability:
Environmental Factor Reaction
Heat Abrupt temperature changes likely to cause fracturing
Light Stable
Chemicals Attacked by hydrofluoric acid
Care and Cleaning:
Type of Cleaning Advisability
Ultrasonic cleaning Usually safe, risky if contains liquid inclusions
Steam cleaning Never
Warm, soapy water Safe
Imitations:
Colored CZ
Colored YAG
Alternatives:
Emerald
Green sapphire
Green zircon
Peridot
Tourmaline
Tsavorite
garnet
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