Gemstone Guide

 

 

 

 Agate. A form of chalcedony which forms from layers of quartz usually showing varicolored bands. It usually occurs as rounded nodules or veins. The composition of agate varies greatly, but silica is always predominant, usually with alumina and oxide of iron. Agates are found in the USA, Brazil, Mexico, Africa, Egypt, India, Italy, Nepal, Germany and Asia.

 

  Alexandrite. Alexandrite is a variety of chrysoberyl. Named after Czar Alexander II, it is a color change stone that is green in daylight and light red in artificial light.Mined in Sri Lanka, Rhodesia, Brazil, Burma, Tasmania and U.S.

 

 Amazonite. Amazonite is a gem variety of microcline feldspar. It displays a shiller of light which is caused by . Amazonite varies from bright verdigris green to a bluish green. Amazonite is mined in the United States, Brazil, Zimbabwe, Russia, Australia and Namibia.

 

Amber. Amber is a fossilized resin from pine trees. Amber deposits have been found that are over 150 million years old, but most amber used in jewelry or ornamentals is between 20-90 million years old. As the sticky resin oozed from ancient pine trees, small insects, plant material, feathers and other small objects in the path of the flow became entrapped. Over time, the resin was encased in dirt and debris and through a process of heat and pressure it fossilized to become amber. Amber exhibits a resinous luster. Most amber that has been used in jewelry is from the region of the Baltic Sea or the Dominican Republic.

 

Amethyst. Amethyst is the purple variety of quartz. To be called amethyst, it must be the purple form of quartz although it can display a wide range of purple shades including purple, lilac and mauve. The most valuable amethyst is a deep purple.

Amethyst is found in geodes and alluvial deposits all over the world and occurs in both crystalline or massive forms. It is a 7 on the Mohs scale of hardness. "Green amethyst" is a misnomer since the term "amethyst" applies only to the purple variety of quartz. However, that doesn't stop the marketing of these less valuable pale amethyst stones after irradiation and/or heat treatments turn the color green. Properly, after treatment, this stone should be marketed as Prasiolite or Green Quartz, not green amethyst, and it should not be marketed as "rare" since there is an abundance of pale lavender quartz which can be treated to produce a light spring green stone.

 

Ametrine. This is a bicolor variety of quartz containing both amethyst and citrine colors. The stone is usually cut in facets in a rectangular shape to show both the yellow and purple colors. The Anahi Mine in Bolivia is the major source for ametrine.

 

Ammonite Fossil. Ammonite Sea faring creatures from the Cretaceous period, ammonites were mollusks that built a chambered shell in which they would pump air into the empty chambers which allowed them to float at different levels of the ocean. Ammonites lived approximately 400 million years ago.

 

Aquamarine. The aquamarine is a member of the beryl family and ranges in color from a pale almost colorless blue to blue-green to pure blue. Some of these stones are heated to enhance their color and change a light colored stone to pure blue. Usually faceted,aquamarines are also cut as cabochons and may then exhibit asterism. Legend tells of sailors who wore aquamarines to keep them safe and to prevent seasickness. The most valuable aquamarines come from Brazil.

 

Aventurine. Aventurine is a translucent to opaque variety of microcrystalline quartz. Small inclusions of shiny minerals give the stone a sparkling effect known as aventurescence. Aventurine ranges in color from green, peach, brown, blue and a creamy green. Mohs hardness is 6.5. (Pronounced: ah-ven-shur-ine) Aventurine is found in India, Chile, Spain, Russia, Brazil, Austria, and Tanzania.

  

Azurite. Azurite is a copper-based mineral that ranges in color from very deep blue to pale blue. A relatively soft mineral, azurite has a hardness of 3.5 to 4.Azurite is found in many areas of the world including: Australia, the southwestern USA, France, Mexico, Morocco, Namibia, Zaire, and Europe.Malachite, which is another copper-based mineral, is often found with azurite. When found together it is called Azurite-Malachite.

 

Bloodstone. Bloodstone is a soft green jasper mottled with red spots from iron oxide. A type of Chalcedony it is also known as Heliotrope. Bloodstone is a relatively soft stone and is one of the ancient birthstones for February or March.

 

Boulder Opal. Boulder Opal forms on a dark ironstone base (the host rock) and occurs as a thin uneven layer adhering to the ironstone. Because of the uneven layers, sometimes part of the ironstone is visible on the surface of the stone. Boulder opal is found in a wide range of colors including: green, blue, aqua, and pink. Boulder opal is found in Australia where precious opal forms in veins and patches within brown ironstone boulders.

 

Bone. Most bone used in jewelry is either animal bone (frequently cow bone) or petrified dinosaur bone. It is used to make beads and cabochons and is sometimes carved to make a solid bangle or ring. Abundantly available, it is often used in place of more expensive ivory, however, bone is not as fine grained as quality ivory and the color is "whiter" rather than "ivory" colored. Agatized dinosaur bone is found in colors of red, brown, yellow and black.

Cabochon. A stone which has been cut with a rounded convex surface and a flat base. It may be high domed or almost flat and can be cut in round, oval, square or freeform shapes. A cabochon has no facets. This is one of the oldest and simplest cuts. This form of cutting is most often used on stones like turquoise, lapis, opals, various forms of quartz and other opaque and semi-opaque stones which may be cut either freeform or calibrated. Freeform cabochon Sometimes, lower quality precious and semiprecious stones such as ruby, amethyst, citrine and garnet are also cut en cabochon. By their nature, stones like druzy cannot be domed or polished and it is now common to call any stone that is not faceted a cabochon. (pronounced:cab-uh-shon) Cabochon.

Cameo. Cameos are carvings traditionally done on shell or stone where the design is carved in relief with a contrasting colored background. This is the opposite of the intaglio. The most recognized cameos today are of florals and the head and shoulders of Victorian women but carvings of mythological gods and goddesses, scenes and military heroes were popular as far back as Green and Roman times.

Cameos have been collected and worn by many including Napoleon, Queen Elizabeth, Catherine the Great and Queen Victoria. Pope Paul II collected cameos and it has been noted in some historical references that because he wore so many heavy cameo rings his fingers were cold from lack of circulation and this ultimately may have influenced his death.

Carnelian. Carnelian is a form of chalcedony that ranges in color from red to orange. It is a translucent stone that may contain bands of color. This stone has been used to offer protection during travel and is thought to help with diseases of the blood including the relief of menstrual cramps. It is found in India, Australia, Brazil, Germany, Madagascar, Russia, South Africa, and the USA.

Chalcedony. Chalcedony, pronounced kal-sed-uh-nee, is a micro crystalline member of the quartz family. It is found all over the world and is one of the oldest stones used by humans for decoration. It has a waxy luster and may be opaque as in jasper, petrified wood, and bloodstone or translusent to transparent in agate, carnelian, or chyrsoprase. In the jewelry trade, the term chalcedony usually refers to white, gray, or blue translucent stones such as "Blue Chalcedony".

Other forms of chalcedony are onyx, sard, sardonyx, petrified dinosaur bone, chert, flint, fire agate and dendritic agate. Because it is a porous stone, it can be stained or dyed to enhance or change the natural color of the stone. Agates are often dyed while most onyx used for jewelry purposes is dyed black, thus the name "black onyx".

 

 

Charoite. Chariote is a fairly recent discovery found in Russia in 1978 in the Murun mountains in Yakutia, near the Charo River. This is the only known location for this rare mineral.
It ranges in color from a light lilac to a deep purple and can be mottled with gray, white and black inclusions. The chatoyant variety in a bright deep purple, is usually considered more valuable than the non-chatoyant variety although both are used in jewelry and compliment a number of other stones.

 

Chrysocolla. An inexpensive, usually opaque, blue to blueish green mineral, Chrysocolla is most often cut as a cabochon for jewelry purposes but high quality, translucent stones know as "gem chrysocolla" are highly prized and can be considerably higher in cost. Another form is "drusy chrysocolla" where the base stone is covered with tiny clear quartz crystals and is often found in botryoidal form. Chrysocolla was also used by the ancient Greeks as an ornamental stone. Often confused with turquoise, it is a copper bearing mineral found wherever copper deposits occur in Australia, Chile, Democratic Republic of Congo, England, Israel, France and Zaire with notable deposits Arizona, Utah, New Mexico and Pennsylvania in the USA.

 

Chrysoprase. A gemstone variety of chalcedony (a form of quartz) Chrysoprase contains small quantities of nickel which is responsible for its apple-green color. It is cryptocrystalline, which means that it is composed of very fine crystals that cannot be seen as distinct particles under normal magnification. Due to its comparative scarcity and unusual green color, chrysoprase is one of the most prized varieties of quartz and commands top dollar for quality stones. Also spelled chrysophrase. It is found in Australia, Brazil, the Ural Mountains, and the U.S. and is the rarest of the chalcedony group.

 

Citrine. Citrine is a variety of quartz ranging in colors of yellow, yellow-brown, orange, dark orange-brown, or reddish-brown. Brazil is the leading producer of naturally mined citrine, however, most commercial citrine on the market today is actually artificially heated amethyst or smoky quartz. Citrine crystals may form together with amethyst or smoky quartz to form a BI-colored quartz called ametrine. The name comes from the French word for lemon, "citron".

 

Dichroic Glass. A glass which contains ultra-thin layers of aluminum, chromium, silicon, zirconium or the metal alloy titanium. The colors are almost holographic in appearance. Addition of the various elements is what produces the bold and dramatic colors. Colloidal gold may also be added. The appearance will be different depending on whether the light is reflected or transmitted.

 

Dinosaur Bone. Petrified Dinosaur Bone or "dino bone" is the result of fossilized bone from dinosaurs in which the cellular structure has been replaced with quartz, leaving the bone structure intact. It isnow illegal to dig dinosaur bone on government lands so there is less available on the market and the price for quality stone has increased significantly.

 

Drusy, Druzy (sometimes referred to as: druse, druzy) is a layer of tiny quartz crystals that form on a host stone. The cavity inside a geode is sometimes filled with drusy quartz crystals. Although the quartz crystals may be the source of the color (amethyst, citrine), usually it is the host stone's color (chrysocolla, uvarovite garnet) that shows through the quartz and gives the stone its color. (pronounced: dru-zee).
Titanium drusy is agate drusy that has been coated with titanium in a vacuum chamber. It produces a permanent metal coating in spectacular shades of bight, dark blue or an iridescent white.

 

Emerald. Emerald is the green member of the beryl family. Traces of chromium and vanadium in the crystalline structure are what produce the green color. These gemstones were mined by the Egyptian Pharaohs as early as 3000 B.C. and the ancient Incas and Aztecs of South America regarded them as holy. Today, the best and most valued, stones come from Colombia. Mohs hardness 7.5 - 8.

Facet One of the flat polished surfaces cut on a gemstone which allow the cut stone to sparkle and reflect light. Diamonds, emeralds, sapphires, and rubies are normally faceted.

Fire. Fire in a stone refers to the streaks and flashes of brilliant color(s) seen when the stone is rotated or moved in a natural or artificial light source.Opals are noted for their fire.

 

 

Freeform. A stone cut in an unusual or non-calibrated shape. Freeform cut ammolite.

 

Garnet. Garnets occur in every color except blue and most varieties are named for their color. Rhodolite is a purplish red, hessonite is the name for an orange, cinnamon, or pinkish variety. Tsavorite is the name given to dark green grossularite. Uvarovite and demantoid are also green varieties. Named varieties of garnet include Andradite, Tsavorite, Grossularite, Essonite, Pyrope, Almandine, Spessartite, Melanite, Allochroite, Ouvarovite, Demantoid, and Rhodolite.

Gemstone Today, the common definition of a gemstone is any precious or semiprecious stone, rock or mineral. The explicit definition of a gemstone is a precious stone: diamond, ruby, sapphire, emerald and precious opal. Semiprecious stones are any other rocks, minerals, or petrified material that is not classified as precious and which is used in jewelry or collected. Some semiprecious stones include: agate, topaz, carnelian, and jasper, lapis lazuli, jade and turquoise.

Inclusion In gemstones, an inclusion is any solid, liquid, or gaseous foreign body enclosed in the mineral or rock. The price of amber can vary greatly based on the type of inclusions and clarity of the stone. Amber that contains complete bodies of prehistoric bugs or a well defined fern or leaf can bring a high price, while small bubbles of gas/liquid add only interest to the stone but do not increase the value significantly. Gaseous inclusions in amber. Quartz is another clear stone that when embedded with well defined needle like rutile inclusions can demand a high value. Inclusions of rutile in quartz.

 

Iridescent. A gem displaying rainbow-like colors is called iridescent. Iridescence is caused by the reflection of light from the jewel. Mother of pearl is one example of iridescence used in jewelry. Iridescent mother-of-pearl.

 

Jade. An opaque, semiprecious stone found in shades of green, light purple, yellow, pink and creamy white shades. The term jade is often used to describe both jadeite and nephrite which are similar in appearance and use. The best quality jade comes from Myanmar (formerly Burma). Jade is not only a hard stone, 6.5 to 7 on the Mohs scale, but is also an extremely tough stone which allows it to be cut as a solid piece and used for a ring or bracelet.

 

Jasper. Jasper is an opaque and fine grained variety of chalcedony quartz.
It is found all over the world in all colors including: red, brown, pink, yellow, green, grey/white and shades of blue and purple and is often spotted (Dalmatian), striped (banded jasper), and/or multi colored (picture jasper, poppy jasper).

 

Labradorite. A type of transparent or translucent feldspar which displays strong iridescence (labradorescence). It is a grayish-green but displays bright flashes of green, blue and sometimes yellow-gold colors when viewed from different angles.
Originally found in Labrador, Canada, there are also deposits in Mexico, Russia and the US.
A brilliantly colored form called Spectrolite is found in Finland.

 

Lapis Lazuli. (Lazurite) Top quality lapis is a strong blue, sometimes with a hint of violet. The value of lapis decreases with the presence of white patches (calcite),but small veins of pyrite can increase the value (presence of pyrite is often a personal preference).
The finest Lapis Lazuli comes from Afghanistan where it has been mined for centuries. It is also found in Siberia, Chile, the U.S., Pakistan, and Canada.

 

Mabe Pearl. Mabe pearls are dome-shaped on one side and flattened on the other. They grow attached to the inside shells of oysters. Because the pearl grows against the inside shell, instead of in the mollusk's body, these type pearls are set into rings, earrings and pendants using prongs or bezels to conceal their relatively flat backs.Mabe pearls are cultured in the pearl fields of Japan, Indonesia, French Polynesia and Australia.

 

Malachite. Malachite, a hydrous carbonate of copper, is a popular opaque stone with bands of green and black. Many beautiful specimens of malachite contain other minerals, such as azurite, cuprite, or chrysocolla. Malachite can be found in Zaire, USSR, Germany, France, Chile, Australia, Arizona and New Mexico/USA. It is a relatively soft stone with a hardness of 4 on the Mohs scale. Azurite malachite.

 

Mohs Scale. The Mohs Scale of Hardness measures a substance's hardness or how resistant it is to being scratched. The scale ranges from 1 to 10. For example, a diamond (hardness = 10) will scratch garnet (hardness = 6.5-7.5), but not the other way around, so a diamond is harder than garnet. See hardness for scale of stones.

 

Onyx. A variety of chalcedony quartz, often with parallel banding. When chalcedony is variegated it is called agate. Black onyx may be opaque or translucent and although it does occur naturally in black, it is usually dyed to darken its color. White onyx is a semi translucent white to whitish-yellow stone that was often used in Victorian jewelry for cameos. It has a hardness of between 6.5- 7 on the Mohs scale.
Natural black onyx is a brittle stone requiring care during cutting or carving.

Originally, almost all colors of chalcedony from white to dark brown and black were called onyx. Today when we think of onyx we often preface the word with black to distinguish it from other varieties of onyx that come in white, reddish brown, brown and banded.
A variety of onyx that is reddish brown with white and lighter reddish bands is known as sardonyx.

 

Opal. Most opal is 50-65 million years old, dating back to the time of dinosaurs in the Cretaceous period. Opal formed as silica from decomposing rocks that mixed with ground water and formed a silica gel that hardened in underground cavities and fissures. There are two distinct types of opal, common and precious. The way the silica particles form determines which type. In precious opal, silica particles are packed in regular rows and layers. Moving the stone causes light to diffract, or split, as it grazes the opal surface. This light diffusion shows iridescent flashes of green, blue, aqua and sometimes yellowish or red colors which are referred to as "fire".
Opal is found in a wide range of colors including: green, blue, aqua, and pink.

 

Orthoceras. An extinct member of the cephalopod class with a long, straight, conical shell which could grow as long as 60 feet. The interior is divided into numerous chambers. These invertebrates swam the ocean by using a jet propulsion type system that expelled water from the chambers thus pushing them forward. They are related to the modern day squid, cuttlefish, and octopus and date back 350 million years ago. Fossilized cephalopods are found in the Sahara Desert, Morocco.

 

Petrified Wood. Petrified wood is wood that has fossilized leaving a stone like replica of the original wood. Petrified wood is also called Xyloid jasper or jasperized wood. Palmwood is a specific type of fossilized wood from ancient palm trees characterized by dark spots.

Precious Gemstone Diamond, ruby, sapphire, emerald and precious opal are the precious gemstones. Any other rock or mineral is referred to as semiprecious stone or just a rock.

 

Quartz. Quartz is the most common mineral on earth. It is a crystalline mineral that comes in many forms, including amethyst, citrine, rock crystal, rose quartz, tiger's eye, chalcedony (agate, carnelian, aventurine, chrysoprase, jasper). Rutilated quartz is clear quartz embedded with golden rutile needle like inclusions. Tourmalinated quartz is embedded with needle like inclusions of tourmaline.

Semiprecious Gemstone Any stone that is not classified as precious . Some examples are: turquoise, aquamarine, agate, jade, pearl, rose quartz, aventurine.

 

Sterling Silver. Sterling is silver with a fineness of 925 parts per thousand or 92.5% silver and 75 parts per thousand or 7.5% copper. Copper is added to the alloy to increase the silver's hardness.

 

Translucent. As a jewelry term, this applies to a gemstone that allows light to pass through the stone but with enough diffusion to prevent the ability to see distinct images through the stone.A moonstone is a translucent stone.

 

Transparent Used to describe stones that are clear and transmit light so that objects can be seen through the stone. Many fine quality colored stones such as ruby, citrine, or topaz are transparent. However, due to the depth of color or inclusions, you may not be able to discern an exact representation of the object as you would if looking through a transparent window glass. Quartz is another example of a transparent stone, it may be as clear as a window pane and was sometimes used as such in early times.

 

Zircon Zircons are very common minerals which occur naturally in clear, yellow, brown, orange and reddish-brown colors. Zircon is frequently heat treated to enhance or alter their color. Mohs scale: 6.5-7.5.

Many people confuse the natural gem zircon with cubic zirconia which is a man-made, synthetic used as an inexpensive alternative to a diamond. Note that these are completely different materials.