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

Treatment

Heating

Description

orange or orangy red color in yellow to brown agate

Purpose

Improves color

Stability

Permanent

Prevalence

common

Care and Cleaning:

Type of Cleaning

Advisability

     Steam cleaning

Not recommended

Ultrasonic cleaning

Not recommended

Warm, soapy water

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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