Precious and Semi-Precious Stones

Howlite is frequently dyed blue to resemble turquoise, and it makes a most convincing simulant. The white material is relatively unexciting in appearance. It should not be difficult to find numerous small faceted huebnerites among larger gemstone collections.

Certainly ample material exists to cut a number of such gems, although they are rarely offered for sale. Faceted chondrodite is almost unknown, a pity since the color is very rich and the material is hard and durable enough for wear. Cutting presents no great difficulty, but rough is virtually unobtainable, and only tiny stones could be produced. The same is true for norbergite and humite.

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Hureaulite can show rich and lively pink, rose, and orange colors. However, this collector's gem is rarely cut. Hurlbutite is an extremely rare mineral. Minute, colorless faceted stones have been cut from fragments. Hydrogrossular differs from the other garnets in that it is never transparent. It ranges from translucent to opaque. The most common color is a bluish green, but they are also found in pink, white, and gray. Hyperitdiabas is one of the most outstanding minerals I have encountered in recent years. Its appearance striking beautiful and a close inspection reveals still more delights.

It has all the properties of a commercially important gemstone, but its rarity will keep it on the sidelines. When properly cut it is as bright and attractive as the grossular garnets, which it so strongly resembles. The complexities of its chemistry lead to a huge range in properties and colors. Cuttable material is known from Italy brown and green , Quebec pale green, bright yellow , New York brown , Pakistan gree Inderite is very soft and difficult to cut, and only a few stones have been cut by hobbyists.

There is plenty of cuttable material in existence, and although the material comes from only a few localities, it is not considered a great rarity. The surface of cut stones may become white and cloudy after cutting; care must be taken in storage and to dry the stones after cutting.

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This stone, which represents one of the few relatively available and affordable blue stone options, is rapidly gaining in popularity. Arguably the gain is due more to exposure in mail order catalogs and on cable shopping channels than to promotion by traditional jewelry stores. Run of the mill stones often have a steely, inky or washed out blue color, but the best specimens can riva One of two distinct minerals commonly known as jade, jadeite is the rarer and harder variety.

However, durable jadeite can be found in many colors and is well-suited for both intricate carvings and cabochons. Jasper is an opaque, solid or patterned variety of cryptocrystalline quartz. All types of jasper take an excellent polish, are trouble free to care for, and hardy enough for all jewelry uses. These stones are usually cabbed, sometimes carved, but seldom faceted. Until the Namibian material was found, jeremejevite was an exceedingly rare mineral available only in microscopic grains.

The African crystals are amazing in being both large and gemmy. Few gems have been cut from the material since the crystals are prized by collectors and the extent of the find is unknown. The crystals are not abundant at the locality, so jeremejevite will remain Historically a popular black gem, jet has declined in popularity in modern times. Although jet jewelry has been long associated with mourning, this organic gem can be made into large, eye-catching beads, carvings, and even faceted pieces. It is micaceous; consequently, it is extraordinarily difficult to facet, which has severely limited the availability of cut gems.

It would have to be handled with great care to avoid cleaving. A few clean, well-cut gems do Perfect basal cleavage; micaceous; laminae exist, nonetheless, a testimony to the perseverance of hobbyists! Kornerupine is generally dark brown or green and not very attractive due to the somber colors. The light green material from Kenya is much more appealing, but the sizes are always small under 3 carats as a rule.

The color is caused by traces of Fe, Cr. Despite the fact that many stones are in museums Kurnakovite is similar to inderite. Both are colorless and very uninteresting as faceted gems, which is why very few have been cut. The material is obtainable in large size, but softness and cleavage make cutting a real chore. Kyanite is very rare as a faceted gem, especially if free from inclusions and flaws. The material is extremely difficult to cut because of its perfect cleavage and the extreme variability in hardness in different directions in the same crystal.

A few catseye kyanites are known to exist. An overview on Labradorite Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of Labradorite. This material is nondescript and is cut solely as a curiosity. The gems are soft, pale colored, or colorless, with no fire. Few cut stones have been reported, but this may be due to a lack of interest rather than a lack of suitable rough. The gem known as lapis lazuli, or simply lapis, is actually a rock, composed of lazurite, hauyne.

Lazurite itself may be considered a sulfurrich hauyne. Calcite and pyrite in various percentages are also present in the rock. The finest lapis is considered to be a solid, deep blue with no white calcite spots and jus Lazulite makes a magnificent, deep blue gemstone. Although the mineral itself occurs widely, gem-quality rough is limited. Specimens are prized by collectors but can also be faceted with care or cut into cabochons for jewelry. Transparent, faceted gems are extremely rare.

Reddish granular or massive lepidolite is usually slabbed for ornamental purposes, such as ashtrays paperweights, and bookends. Faceted micas are virtually nonexistent because of the perfection of the cleavage and the variable hardness within crystals. Although abundant in various lava rocks, leucite is extremely rare in gem-quality form and often has a milky or cloudy look. Faceted stones as well as well-shaped crystals are prized by collectors. The blue color of linarite is magnificent, and it is a pity that large facetable rough has not been found.

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Clean areas of crystals are usually very small, and breakage in cutting due to the softness and cleavage of the mineral further complicates the salvaging of a large gem. This is a lovely collector item and an extremely rare one. Ludlamite has a lovely green color but is too soft for wear. Large crystals are known from only a few localities, and cut stones are extremely rare. Gems of completely transparent magnesite are both rare and beautiful. The huge birefringence is obvious even in small stones, and larger gems have a sleepy look, or fuzziness, due to the doubling of back facets as seen through the table.

Faceted magnesite is rarely seen, and the material is relatively difficult to cut. Facetable crystals come only from Brazil. Malachite is one of the most popular and beautiful of decorative stones. Malachite can with great care be turned on a lathe to make goblets and candlesticks. It is extensively used to make cabochons, beads, boxes, and carvings of all kinds. Fibrous aggregates are packed masses of crystals, and these also take Mali Garnet, one of the rarer varieties within the garnet group, is a mixture of the species grossular and andradite, therefore it is sometimes called "grandite.

That means the crystal structure is basically the same throughout the group, but some of the chemical formulas differ. At certain key points throughout the While the colors of spessartite garnet gemstones cover a wide range of orange shades, the mandarin garnet is as pure orange as this variety can be. Transparent material is light enough in color to allow lots of light to enter and leave a cut gem, and properly cut stones are lively and brilliant.

Cutting is difficult because of the cleavage. Marcasite has a long history of use as a decorative and jewelry material. However, this brassy colored, metallic stone is quite brittle and seldom seen in modern jewelry. Meliphanite is an extremely rare gemstone, and perhaps fewer than faceted stones have ever been cut. Mellite is a rare and unusual organic gemstone. Microcline is a variety of feldspar. The only microcline you are likely to encounter is amazonite.

Ranging in color from pale yellow to brown, reddish, and green, microlite cabochons are prized by collectors.

List of Precious and Semi-Precious Gemstones by Name (A-Z)

Faceted gems are very beautiful but extremely rare. Milarite was originally known as a green mineral, until fine yellow crystals were discovered in Mexico in Larger Mexican crystals have transparent areas and have been faceted into small gems of pleasant appearance but great rarity. Millerite has a rich, attractive yellow color. Massive millerites can sometimes be cut into cabochons but are too soft for jewelry use. However, millerite crystals can also have a striking, hair-like appearance. Faceted mimetite is one of the rarest of all gems since only one pocket of transparent crystals has ever been found at Tsumeb , and few of these crystals have been cut.

Orange and yellow cabochons are richly colored but are too soft for wear. Moldavite is a transparent to translucent olive to bottle green tektite, first found in at the Moldau River in Czechoslovakia. In general, tektites are natural glasses which are thought to have been created by melting of silica sand or rock by meteoric impact. A popular idea is that the melted material then was flung into the air and cooled into glass as it landed over the area Stones can be an attractive yellow or brown color but are usually small. Moonstone or "Adularia", an orthoclase feldspar, was originally named for an early mining site at Mt.

From this tradition we derive the term "adularescence" which is the optical phenomenon of iridescence which creates a billowy, floating blue to white light in this gem. Adularescence is due to diffraction of light as it hits thin, alternating layers of orthocl Compact, fibrous material is cabbed because the fibers provide a chatoyancy that sometimes yields weak catseyes. Coloration in the material is due to staining. This is a relatively unexciting mineral, and gems are equally uninspiring. Nevertheless, it has been reported as being cut for collectors.

A member of the beryl family, morganite shows a range of pink colors due to traces of manganese. Recently, this gemstone has seen an increase in popularity and value. Like most beryls, morganite makes an excellent jewelry stone. The color of Namibian nambulite is a striking orange-red, very intense, and not really like any other gem I have seen.

Cut stones would be both extremely rare and quite magnificent, perhaps bearing some similarities to rhodonite. All three minerals are fibrous or elongated zeolite minerals. Faceted gems are almost always elongated emerald cuts or step-cuts. These inclusions produce a sheen that yields a catseye effect in cabochons. Nephrite is one of the two distinct minerals commonly known as jade. While nephrite doesn't match the variety or the fine green colors found in jadeite, it's even more durable as a gem material for jewelry and carved objects.

An overview on Neptunite Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of Neptunite gems. Gem cutters typically carve this gem material into cabochons for jewelry use. Obsidian is an attractive material and displays a wide variety of appearances. Snowflake obsidian, with spherulites of cristobalite, is widely used in jewelry as beads and cabochons.

Some of these have been faceted. Green, blue, and reddish transparent Oligoclase gems are feldspars that are part of a solid state series between albite and anothrite. Opals are in a class by themselves. As a species, opal is so unique it has its own descriptive vocabulary. More than any other gem, each opal is distinctly individual.

Opals are also the most delicate gemstones commonly worn and require special care. The article points out that prior to the finds of substantial amounts of facetable crystals in Oregon, most sunstone, much of which came from the Orient, was used for cabbing material, or in the production of pale yellow, low value, faceted goods. Such is the case no more. Orthoclase is best known for moonstone.

It is occasionally a transparent, faceted gem. Note that moonstone is occasionally a labradorite. Until , only three painite crystals were known to exist. Since then, additional discoveries have produced many more specimens of this deep red gemstone, but facetable material remains very rare. This unusual, parchment-like mineral can be cut into cabochons or carved. Cerulean blue papagoite crystals are too small for faceting. However, massive material mixed with quartz can be cabbed, while quartz crystals with papagoite inclusions make striking specimens for collectors.

The amphibole group is very large and extremely complex and contains numerous distinct species that vary subtly in chemistry and physical properties. The identity of a specific amphibole is determined An overview on Parisite Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of Parisite gemstones. Pearls are the only gems found within living creatures, both salt and freshwater mollusks. However, most pearls on the market today are cultivated, since they now occur extremely rarely in nature.

While they require special care, pearls have an enduring appeal for jewelry, particularly as the traditional June birthstone. Fibrous pectolite has long been a curiosity for gem collectors. Compact material can make wonderful cabochons, and transparent crystals are rare and usually tiny. Larimar, blue pectolite from the Dominican Republic, has become a popular jewelry stone. Pentlandite resembles other yellowish metallic minerals and is cut by collectors as a curiosity. The cut stones are quite attractive but too soft for hard wear. Periclase has been synthesized in large masses in the laboratory, but these have no market significance.

A faceted natural periclase would be a great rarity due to the extreme scarcity of suitable faceting rough. The expected size would be less than 1 carat. Peridots have been prized as jewelry stones since ancient times. Always green in color but with considerable variations, their particular shades depend on their locality of origin. Peristerite is primarily oligoclase with a complex mixture of feldspars.

It has iridescence that is either blue or white. Perthite is a blend of microcline, albite and oligoclase. It is usually brown and white. May have gold or white iridescence. Gem-quality, colorless, facetable petalite is rare and desirable to collectors. More so if the stones are large and free of inclusions. Rare phenakite is a very hard gem material suitable for jewelry. Usually colorless, cut stones have little fire but can be very bright.

Rare phosgenite typically shows pale colors. This material is difficult to cut and too soft for jewelry wear. However, its strong yellowish fluorescence appeals to collectors of unusual gemstones. Unfortunately, this gem is quite fragile and difficult to cut, and few large facetable crystals exist. Colorless pollucites lack fire when cut and are usually small. However, this very rare cesium mineral is a coveted collector's gem. An overview on Powellite Jewelry and Gems. Covers details and essential information on the physical properties and characteristics of Powellite gemstones.

Prehnite is popular as a cabochon material among hobbyists because of its lovely green and blue-green to yellow colors. Completely transparent material is extremely rare but might be found in crystals from Asbestos, Quebec. Yellowish to greenish translucent material from Australia has been faceted and makes a striking cut gemstone with a rich color and interesting appearance, with a An overview on Prosopite Jewelry and Gemstones.

Covers details and essential information on the physical properties and characteristics of Prosopite gems. In reflected light, they have a dark gray, metallic luster. In transmitted light, the dark red of the garnet shows through. Proustite crystals have magnificent red colors and good brilliance. Although facetable, they're too soft for jewelry use but highly desired as collector's gems. The gem variety of pumpellyite, chlorastrolite, is best known from the Lake Superior district of the United States.

It typically forms aggregates of packed fibers that are mixed with other minerals, resulting in a green and white pattern reminiscent of tortoise shell. The effect is best observed when the fibers are in radial clusters that yield circular markings. This material is never transparent and is too soft for wear. However, cabochons are a magnificent purplish rose hues that have essentially no counterpart in the gem world. The material is available from Namibia in abundance and at low cost.

Pyrargyrite is found in a number of localities in well-formed crystals, but these are usually small. However, larger, transparent crystals from Bolivia and Chile have provided a limited amount of cuttable rough. Stones approaching 50 carats have been cut, but these tend to be too dark to be really attractive. They are exceedingly rare, however, since pyrargyrite is seldom transparen It has been used for centuries both in jewelry and as an ore of iron.

The material is very brittle and heat sensitive and requires some care in cutting. Cabochons are sometimes cut, but they have Pyrophyllite resembles talc in many ways and is indistinguishable by eye from soapstone. Chemical tests are needed to distinguish them. Pyroxmangite grains are rare, seldom clean enough to facet, and difficult to cut. However, when cut, they are extremely beautiful and rich in color. An overview on Pyrrhotite Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of Pyrrhotite gems.

An overview on Quartz Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of a Quartz mineral. Quartzite is a rock made up of tightly packed quartz grains. Sometimes, it contains small crystals that reflect light. This material is called aventurine. Although this common arsenic sulfide mineral occurs worldwide, cut gem-quality realgar is extremely rare. This fine, red stone is very fragile, difficult to cut, and nearly impossible to wear. Originally known as bixbite, red beryl is one of the rarest, most desirable, and most expensive gemstones.

Most fine crystal specimens are zealously guarded by mineral collectors and are never faceted. Rhodizite is tough enough to make an excellent jewelry stone. However, it's quite a rare mineral. Faceted specimens are extremely rare and usually small and pale in color. Beautiful rose red to pink rhodochrosite crystals are popular with mineral collectors. Although very soft, opaque material has been fashioned into beads, cabochons, and carvings, while very rare translucent to transparent material has been cut into faceted gems. Rhodolite is a garnet, intermediate in composition between almandine and pyrope.

Its distinctiveness lies in its color, which is nearly always a purplish red. Ranging in color from pink to a fine rose red, rhodonite is a popular material for jewelry and decorative objects. Faceted rhodonite has an intense, beautiful color, but this material has a reputation as one of the most difficult gemstones to cut. A popular variety of colored quartz, rose quartz makes a durable jewelry stone. Although commonly cabbed and carved, more transparent material can also be faceted. Rubellites are tourmalines with reasonably saturated dark pink to red colors and medium to dark tones.

They make excellent jewelry stones, and ruby-red colored specimens without orange or brown overtones are highly prized. Ruby is red corundum, all other color varieties of corundum being referred to as sapphire. That fact notwithstanding, the ruby color range includes pinkish, purplish, orangey, and brownish red depending on the chromium and iron content of the stone. The trace mineral content tends to vary with the geol Though perhaps best known as inclusions within other gems, rutile crystals themselves can be faceted or cabbed as curiosities for collectors. Synthetics can show a variety of colors and have even been used as diamond simulants.

Pearls are one of our most ancient gems with records of commercial harvesting going back years. Their natural occurrence is very rare, with only one in several million shellfish ever producing a pearl. Oysters are the best-known source, but clams, mussels, and abalone also produce pearls. Samarskite is a very heavy material from which lustrous black to brownish cabochons are sometimes cut as curiosities. The material is rather brittle and is not intended for wear.



It is rarely seen or displayed since black stones are not terribly attractive. Sometimes a stone is faceted in the nature of jet or marcasite. Sanidine is a mineral of volcanic rocks, rarely considered a gem. While occasionally brown or yellow, most examples are colorless.

Take Your Passion for Gemstones to a Whole New Level

Few gems have held our attention over millennia as well as sapphire. The pure blue colors and excellent durability of this gem-quality member of the corundum family make for an exceptional gemstone. However, not all sapphires are blue. They come in every color of the rainbow.

Sapphirines are durable but very rare gemstones. Although named after their typically sapphire-blue color, these gems can occur in different hues and display pleochroism, too. Sarcolite is an extremely rare mineral. Although not well known, scapolite would make an attractive gem material for both jewelry enthusiasts and mineral collectors.

It comes in a wide variety of colors and can show dramatic fluorescence and phenomenal effects. They occur in many colors and fluoresce very brightly. If cut properly, scheelites can have tremendous fire. With lovely colors and intense pleochroism, faceted scorodite is a prize for collectors of the rare and unusual. An overview on Sellaite Jewelry and Gemstones.

Covers details and essential information on the physical properties and characteristics of Sellaite gems. Senarmontite is a rare mineral, restricted in occurrence to the presence of antimony sulfide ores. It is much too soft to wear, and the colors are usually nondescript. However, a faceted senarmontite in any size would be a great rarity.

This essentially is another one locality mineral, where very small gems have been cut from an occasional crystal fragment that is not always even transparent. Shattuckite is often mixed with quartz, and data often reported for properties may be erroneous. The cabochons are rich blue in color and very popular, but the material is not abundant and seldom seen on the market. Sea shells are one of our most ancient decorations. Our prehistoric ancestors used to string them into necklaces or hang them from cords as pendants. People still use them this way today. Shortite is an exceedingly rare, not overly attractive mineral.

Cut gems are among the rarest of all faceted stones. The material is a carbonate and is therefore fragile and soft. Siderite is difficult to cut, but this light brown collector's gem has yielded faceted pieces of great beauty. The fibrolite from Burma and Sri Lanka is well known to gem collectors, and highly prized because of its great scarcity. Blue and greenish gems are lovely, although very difficult to cut. Chatoyant material sometimes yields catseye fibrolites, which are also very rare.

The material from Kenya is just as attractive as Burmese fibrolite but seems to be somewhat smaller in size. Simpsonite is an extremely rare gemstone. The material from Western Australia is bright yellow-orange and very beautiful. The mineral is hard and durable, with no cleavage, and could easily become a popular gemstone if it were more abundant. Gems over 1 carat should be considered extremely rare because clean material is a very small percentage of the limited supply of simpsonite tha Long thought to be brown peridot, sinhalite was investigated in and found to be a new mineral.

When cut, it is richly colored, bright, and attractive, and resembles citrine, peridot, or zircon. Large gems are very rare, but smaller stones are available in the marketplace. Some people have reported that it was easier at times to find a large sinhalite for sale than a small one, Smaltite is a collectors oddity, cut only as cabochons.

It is seldom seen in collections since it is not especially distinctive, with a color resembling other metallic sulfides and arsenides. Smithsonite occurs across the globe, but facetable crystals are extremely rare. These gems can show a wide range range of rich colors but are too soft for most jewelry use. Smoky quartz comes in every shade of brown, from a light tan to nearly black.

This gem is known for its large sizes. If you want a really big gem on a very small budget, this could be your stone. Tough, easy to cut or carve, and rich in color, typically blue, sodalite is highly desired by hobbyists. Even stones that lack transparency make lovely faceted gems. Sogdianite is an extremely rare mineral, suitable for cabochons. The color is striking and the material is hard enough to take a good polish. It is usually mixed with other minerals, so the SG and hardness are variable. Chemical analysis may be required to differentiate sogdianite from sugilite, but the latter is far more abundant.

Spessartite is somewhat rare. As with the other garnets, it always occurs in a blend with other species. Gems with the highest spessartite content are a light orange. Those with an almandine content are reddish, to red brown in hue. Sphalerite occurs in many colors. With a dispersion over three times that of diamond and an adamantine luster, faceted specimens make beautiful additions to gem collections. However, they're too soft for most jewelry uses. Sphene, also known as titanite, has rich body colors, strong trichroism, and a fire that exceeds diamond.

Although softer than many more popular gems, sphenes can make wonderful jewelry stones if set and maintained properly. Spinel is an important gem historically because it has been confused with other gemstones, especially ruby. Extraordinarily difficult to cut, spodumene has several colorful varieties, such as hiddenite and kunzite, highly coveted for jewelry. This attractive but rather rare mineral has seldom been cut as a gemstone. Polished slabs and rough material appeared in at a mineral show in substantial quantities, however.

This material is Mexican, translucent to opaque, and medium to dark purple in color. Staurolite crystals in opaque cross shapes are popular gemstones. However, this material is very rarely transparent or facetable. These dark colored gems would make very durable jewelry pieces.

Rare stibiotantalite possesses an interesting mix of physical and optical properties that help distinguish it from other earth-toned gemstones. Stichtite is not facetable, but the pink color is quite striking in cabochons. Cut stones are especially beautiful when there are other minerals present to add splashes of green and yellow.

This material somewhat resembles a pink, granular material from the USSR referred to as canasite. Stolzite is a rare mineral; much rarer than wulfenite and usually occurs in very minute crystals. However, the Australian crystals may be up to 1 inch Colors are usually pale and there is little fire; in addition, the high birefringence doubles back facets and kills the brilliance of the stone.

Cut strontianites are, however, decidedly uncommon and worth pursuing for their scarcity value. What is the color of sugilite? Grape jelly purple is a good description. More popular among consumers in Asia than North America, this is a very rare and beautiful opaque gem material with an unusual appearance. Although sulfur is very abundant, facetable material is not.

Sulfur is also enormously difficult to cut and almost impossible to wear, so faceted pieces have some scarcity value for collectors of unusual gems. Sunstones contain hematite or goethite inclusions, which reflect light in parallel orientation and create a sparkling sheen in gold to brown color shades. These gems may be oligoclase or labradorite in composition and are much admired as a cabochon material among hobbyists. Sometimes you will can see that a pearl, an opal or a jade are listed as a precious gemstone, but more often they are considered semi-precious.

Traditionally, these four precious stones have been the most expensive and sought after stones. The list goes on and on, but some of the more common ones are: This separation between precious and semi precious has no real scientific backing. For example, emerald is a variety of a beryl, so are aquamarines. Emerald is precious while aquamarine is semi precious. When this categorization came about, it was mainly due to the value and rarity differences between the 4 precious gemstones and the rest.

Today some semi precious gemstones can be worth much more than a precious stone. As an example, many natural pearls garner huge prices, often worth more than a low quality precious diamond, ruby, emerald or sapphire. Spinels are another example. Rare or unusual gemstones, generally meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite , axinite , cassiterite , clinohumite and red beryl. Gemstone pricing and value are governed by factors and characteristics on the quality of the stone. These characteristics include clarity, rarity, freedom of defects, beauty of the stone, as well as the demand for them.

There are different pricing influencers for both colored gemstones, and for diamonds. The pricing on colored stones is determined by market supply-and-demand, but diamonds are more intricate. Diamond value can change based on location, time, and on the evaluations of diamond vendors. There are a number of laboratories which grade and provide reports on gemstones. Each laboratory has its own methodology to evaluate gemstones. A stone can be called "pink" by one lab while another lab calls it "padparadscha". One lab can conclude a stone is untreated, while another lab might conclude that it is heat-treated.

Country of origin has sometimes been difficult to determine, due to the constant discovery of new source locations. Determining a "country of origin" is thus much more difficult than determining other aspects of a gem such as cut, clarity, etc. Gem dealers are aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible certificate.

Clear Crystals, Quartz, Precious and Semi Precious Stones in India

A few gemstones are used as gems in the crystal or other form in which they are found. Most however, are cut and polished for usage as jewelry. The picture to the left is of a rural, commercial cutting operation in Thailand. This small factory cuts thousands of carats of sapphire annually. The two main classifications are stones cut as smooth, dome shaped stones called cabochons , and stones which are cut with a faceting machine by polishing small flat windows called facets at regular intervals at exact angles.

Stones which are opaque or semi-opaque such as opal , turquoise , variscite , etc. These gems are designed to show the stone's color or surface properties as in opal and star sapphires. Grinding wheels and polishing agents are used to grind, shape and polish the smooth dome shape of the stones. Gems which are transparent are normally faceted, a method which shows the optical properties of the stone's interior to its best advantage by maximizing reflected light which is perceived by the viewer as sparkle. There are many commonly used shapes for faceted stones.

The facets must be cut at the proper angles, which varies depending on the optical properties of the gem. If the angles are too steep or too shallow, the light will pass through and not be reflected back toward the viewer. The faceting machine is used to hold the stone onto a flat lap for cutting and polishing the flat facets. The color of any material is due to the nature of light itself.

Daylight, often called white light, is actually all of the colors of the spectrum combined. When light strikes a material, most of the light is absorbed while a smaller amount of a particular frequency or wavelength is reflected. The part that is reflected reaches the eye as the perceived color. A ruby appears red because it absorbs all the other colors of white light, while reflecting the red.

A material which is mostly the same can exhibit different colors. For example, ruby and sapphire have the same primary chemical composition both are corundum but exhibit different colors because of impurities. Even the same named gemstone can occur in many different colors: This difference in color is based on the atomic structure of the stone.

Although the different stones formally have the same chemical composition and structure, they are not exactly the same. Every now and then an atom is replaced by a completely different atom, sometimes as few as one in a million atoms. These so-called impurities are sufficient to absorb certain colors and leave the other colors unaffected.

For example, beryl , which is colorless in its pure mineral form, becomes emerald with chromium impurities. If manganese is added instead of chromium , beryl becomes pink morganite. With iron, it becomes aquamarine. Some gemstone treatments make use of the fact that these impurities can be "manipulated", thus changing the color of the gem. Gemstones are often treated to enhance the color or clarity of the stone.

Depending on the type and extent of treatment, they can affect the value of the stone. Some treatments are used widely because the resulting gem is stable, while others are not accepted most commonly because the gem color is unstable and may revert to the original tone. Heat can improve gemstone color or clarity. The heating process has been well known to gem miners and cutters for centuries, and in many stone types heating is a common practice. Aquamarine is often heated to remove yellow tones, or to change green colors into the more desirable blue, or enhance its existing blue color to a purer blue.



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When jewelry containing diamonds is heated for repairs the diamond should be protected with boric acid ; otherwise the diamond which is pure carbon could be burned on the surface or even burned completely up.