Gemstones

A gemstone or gem which is also known as a precious or semi-precious stone, a fine gem, or jewel) is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments. However certain rocks, (such as lapis lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be in the ranks with gemstones as well.

There is no universally accepted grading system for gemstones. Diamonds are graded by the Gemological Institute of America (GIA). Historically, all gemstones were graded using the naked eye. The GIA system included a major innovation: the introduction of 10x magnification as the standard for grading clarity. Other gemstones are still graded using the naked eye

The "four Cs" (color, cut, clarity and carats) was introduced to help the consumer understand the factors used to grade a diamond. With modification, these categories can be useful in understanding the grading of all gemstones. The four criteria carry different weight depending upon whether they are applied to colored gemstones or to colorless diamond. In gemstones that have color, including colored diamonds, it is the purity and beauty of that color that is the primary determinant of quality.

Physical characteristics that make a colored stone valuable are color, clarity to a lesser extent (emeralds will typically have a number of inclusions), cut, unusual optical phenomena within the stone such as color zoning, and asteria (star effects). Color zoning is the uneven distribution of coloring within a gem. The Greeks, for example, greatly valued asteria in gemstones, which were regarded as a powerful love charm, and Helen of Troy was known to have worn star-corundum.

Historically, gemstones were classified into precious stones and semi-precious stones. Because such a definition can change over time and vary with culture, it has always been a difficult matter to determine what constitutes precious stones.

Aside from the diamond, the ruby, sapphire, emerald, pearl which(strictly speaking not a gemstone) and opal have also been considered to be precious. Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a precious stone as well, going back to ancient Greece. Even in the last century certain stones such as aquamarine, peridot and cat's eye have been popular and hence been regarded as precious.

Nowadays such a distinction is no longer made by the trade. Many gemstones are used in even the most expensive jewelry, depending on the brand name of the designer, fashion trends, market supply, treatments, etc. Nevertheless, diamonds, rubies, sapphires and emeralds still have a reputation that exceeds those of other gemstones.

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.

Gem prices can fluctuate heavily or can be quite stable, In general per carat prices of larger stones are higher than those of smaller stones, but popularity of certain sizes of stone can affect prices.

 

Grading

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. To minimize such differences, seven of the most respected labs, AGTA-GTL (New York), CISGEM (Milano), GAAJ-ZENHOKYO (Tokyo), GIA (Carlsbad), GIT (Bangkok), Gübelin (Lucerne) and SSEF (Basel), have established the Laboratory Manual Harmonisation Committee (LMHC,) for the standardization of wording reports, promotion of certain analytical methods and interpretation of results. Country of origin has sometimes been difficult to determine, due to the constant discovery of new source locations. Determining a "country of origin" is 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.

 

Cutting and polishing

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 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 such as opal, turquoise, variscite, etc. are commonly cut as cabochons. 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. Rarely, some cutters use special curved laps to cut and polish curved facets.

 

Color

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 (green & blue), while reflecting the red.

The same material can exhibit different colors. For example ruby and sapphire have the same chemical composition (both are corundum) but exhibit different colors. Even the same gemstone can occur in many different colors: sapphires show different shades of blue and pink and "fancy sapphires" exhibit a whole range of other colors from yellow to orange-pink, the latter called "Padparadscha sapphire".

This difference in color is based on the atomic structure of the stone. Although the different stones formally have the same chemical composition, they are not exactly the same. Every now and then an atom is replaced by a completely different atom (and this could be 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 you add manganese 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.

 

Treatment

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

Heat is used to 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. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in ametrine—a stone partly amethyst and partly citrine. Much aquamarine is heated to remove yellow tones and change the green color into the more desirable blue or enhance its existing blue color to a purer blue.

Nearly all tanzanite is heated at low temperatures to remove brown undertones to give a more desirable blue/purple color. A considerable portion of all sapphire and ruby is treated with a variety of heat treatments to improve both color and clarity.

When jewelry containing diamonds is heated (for repairs) the diamond should be protected with boracic acid; otherwise the diamond (which is pure carbon) could be burned on the surface or even burned completely up. When jewelry containing sapphires or rubies is heated, it should not be coated with boracic acid or any other substance, as this can etch the surface; they do not have to be "protected" like a diamond.

 

Radiation

Just about all blue topaz, both the lighter and the darker blue shades such as "London" blue, has been irradiated to change the color from white to blue. Most greened quartz (Oro Verde) is also irradiated to achieve the yellow-green color.

 

Waxing/oiling

Emeralds containing natural fissures are sometimes filled with wax or oil to disguise them. This wax or oil is also colored to make the emerald appear of better color as well as clarity. Turquoise is also commonly treated in a similar manner.

 

Fracture filling

Fracture filling has been in use with different gemstones such as diamonds, emeralds and sapphires. In 2006 "glass filled rubies" received publicity. Rubies over 10 carat (2 g) with large fractures were filled with lead glass, thus dramatically improving the appearance (of larger rubies in particular). Such treatments are fairly easy to detect.

 

Synthetic and artificial gemstones

Some gemstones are manufactured to imitate other gemstones. For example, cubic zirconia is a synthetic diamond stimulant composed of zirconium oxide. Moissanite, also a synthetic stone, is another example. The imitations copy the look and color of the real stone but possess neither their chemical nor physical characteristics. Moissanite actually has a higher refractive index than diamond and when presented beside an equivalently sized and cut diamond will have more "fire" than the diamond.

Lab created gemstones are not imitations. Diamonds, ruby, sapphires and emeralds have been manufactured in labs to possess identical chemical and physical characteristics to the naturally occurring variety. Synthetic (lab created) corundums, including ruby and sapphire, are very common and they cost only a fraction of the natural stones. Smaller synthetic diamonds have been manufactured in large quantities as industrial abrasives, although larger gem-quality synthetic diamonds are becoming available in multiple carats.

Whether a gemstone is a natural stone or a lab-created stone, the characteristics of each are the same. Lab-created stones tend to have a more vivid color to them, as impurities are not present in a lab and do not modify the clarity or color of the stone

 

Precious Stones

Rubies

A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). The red color is caused mainly by the presence of the element chromium. Other varieties of gem-quality corundum are called sapphires. The ruby is considered one of the four precious stones, together with the sapphire, the emerald, and the diamond.

The prices of rubies are primarily determined by color. The brightest and most valuable "red" called pigeon blood-red, commands a huge premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions may indicate that the stone has been treated. Cut and carat (weight) are also an important factor in determining the price.

Color
Generally, gemstone-quality corundum in all shades of red, including pink, are called rubies. However, in the United States, a minimum color saturation must be met to be called a ruby, otherwise the stone will be called a pink sapphire. This distinction between rubies and pink sapphires is relatively new. If a distinction is made, the line separating a ruby from a pink sapphire is not clear and highly debated. As a result of the difficulty and subjectiveness of such distinctions, trade organizations such as the International Colored Gemstone Association (ICA) have adopted the broader definition for ruby, which encompasses its lighter shades, including pink.

Factors affecting value
Diamonds are graded using criteria that have become known as the four Cs, namely color, cut, clarity and carat weight. Similarly natural rubies can be evaluated using the four Cs together with their size and geographic origin.

In the evaluation of colored gemstones, color is the single most important factor. Color divides into three components; hue, saturation and tone. Hue refers to "color" as we normally use the term. Transparent gemstones occur in the following primary hues: red, orange, yellow, green, blue, violet. These are known as pure spectral hues. In nature there are rarely pure hues so when speaking of the hue of a gemstone we speak of primary and secondary and sometimes tertiary hues. In ruby the primary hue must be red. All other hues of the gem species corundum are called sapphire. Ruby may exhibit a range of secondary hues. Orange, purple, violet and pink are possible. The finest ruby is best described as being a vivid medium-dark toned red. Secondary hues add an additional complication. Pink, orange, and purple are the normal secondary hues in ruby. Of the three, purple is preferred because, firstly, the purple reinforces the red making it appear richer. Secondly, purple occupies a position on the color wheel halfway between red and blue. In Burma where the term pigeon blood originated, rubies are set in pure gold. Pure gold is itself a highly saturated yellow. Set a purplish-red ruby in yellow and the yellow neutralizes its complement blue leaving the stone appearing to be pure red in the setting.

 

Sapphires

Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide. Trace amounts of other elements such as iron, titanium, or chromium can give corundum blue, yellow, pink, purple, orange, or greenish color. Chromium impurities in corundum yield a red tint, and the resultant gemstone is called a ruby. Sapphires are commonly worn in jewelry.

Sapphires can be found naturally, by searching through certain sediments (due to their resistance to being eroded compared to softer stones), or rock formations, or they can be manufactured for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires sapphires are used in some non-ornamental applications, including infrared optical components, such as in scientific instruments; high-durability windows (also used in scientific instruments); wristwatch crystals and movement bearings; and very thin electronic wafers, which are used as the insulating substrates of very special-purpose solid-state electronics.

The sapphire is one of the three gem-varieties of corundum, the other two being ruby -- defined as corundum in a shade of red—and padparadscha—a pinkish orange variety. Although blue is their most well-known color, sapphires may also be colorless, and are found in many colors including shades of gray and black.

The cost of natural sapphires varies depending on their color, clarity, size, cut, and overall quality – as well as their geographic origin. Significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, Madagascar, East Africa, and in North America in a few locations, mostly in Montana. Sapphire and rubies are often found together in the same area, but one gem is usually more abundant.

Blue sapphire color in gemstones breaks down into three components: hue, saturation, and tone. Hue is most commonly understood as the "color" of the gemstone. Saturation refers to the vividness or brightness or "colorfulness" of the color, and tone is the lightness to darkness of the color. Blue sapphire exists in various mixtures of its primary blue and secondary hues, various tonal levels shades and at various levels of saturation (vividness).

Blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet, and green are the most common secondary hues found in blue sapphires. Violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative. Blue sapphires with any amount of green as a secondary hue are not considered to be fine quality. Gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue and therefore has a distinctly negative effect.

The color of fine blue sapphires can be described as a vivid medium dark violet to purplish blue where the primary blue hue is at least 85% and the secondary hue no more than 15% without the least admixture of a green secondary hue or a gray mask. Yellow and green sapphires are also commonly found.

Pink sapphires deepen in color as the quantity of chromium increases. The deeper the pink color the higher their monetary value as long as the color is tending towards the red of rubies.

Sapphires also occur in shades of orange and brown, and colorless sapphires are sometimes used as diamond substitutes in jewelry. Padmaraga sapphires often draw higher prices than many of even the finest blue sapphires.


Padparadscha
is a pink-orange corundum, with a low to medium saturation and light tone, originally being mined in Sri Lanka, but also found in deposits in Africa & Vietnam. Padparadscha sapphires are rare; the rarest of all is the totally natural variety, with no sign of treatment.

Star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism; red stones are known as "star rubies". Star sapphires contain intersecting needle-like inclusions following the underlying crystal structure that cause the appearance of a six-rayed "star"-shaped pattern when viewed with a single overhead light source. The stones are cut en cabochon, typically with the center of the star near the top of the dome.

The value of a star sapphire, however, depends not only on the weight of the stone but also the body color, visibility and intensity of the asterism.

 

Emeralds

Emerald is a variety of the mineral beryl colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the 10 point Mohs scale of mineral hardness. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor.

Scientifically speaking, color is divided into three components: hue, saturation and tone. Emeralds occur in hues ranging from yellow-green to blue-green, with the primary hue necessarily being green. Yellow, blue, and red — the hues found adjacent to green on the spectral color wheel — are the normal secondary hues found in emeralds. Only gems that are medium to dark in tone are considered emerald; light-toned gems are known instead by the species name green beryl. In addition, the hue of an emerald must be bright (vivid).

Emerald tends to have numerous inclusions and surface breaking fissures. Unlike diamond, where the loupe standard, i.e. 10X magnification, is used to grade clarity, emerald is graded by eye. Thus, if an emerald has no visible inclusions to the eye (assuming normal visual acuity) it is considered flawless. Stones that lack surface breaking fissures are extremely rare and therefore almost all emeralds are treated, "oiled", to enhance the apparent clarity.

Eye-clean stones of a vivid primary green hue with no more than 15% of any secondary hue or combination (either blue or yellow) of a medium-dark tone command the highest prices. This relative crystal non-uniformity makes emeralds more likely than other gemstones to be cut into cabochons, rather than faceted shapes.

 

Opal

Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl and basalt. Opal is the national gemstone of Australia, which produces 97% of the world's supply.

Opal's internal structure makes it diffract light; depending on the conditions in which it formed it can take on many colors. Opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semi-transparent. For gemstone use, its natural color is often enhanced by placing thin layers of opal on a darker underlying stone, like basalt.

There are other kinds of common opal such as the milk opal, milky bluish to greenish (which can sometimes be of gemstone quality); resin opal, which is honey-yellow with a resinous luster.


Semi-Precious Stones
Garnet

The name "garnet" comes from 14th century Middle English word gernet meaning 'dark red', from the Latin granatus granatus coming from granum (grain, seed) + suffix "atus", possibly a reference to "mela granatum" or even "pomum granatum" ("pomegranate", scientific name: "Punica granatum"), a plant whose abundant vivid red arils contained in the fruit are similar in shape, size, and color to some garnet crystals.

There are six common species of garnet are recognized by their chemical composition. They are pyrope, almandine, spessartine, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series: pyrope-almandine-spessarite and uvarovite-grossular-andradite. Because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this mineral group shows a range of hardness on the Mohs Scale of about 6.5 to 7.5. The harder species, like almandine, are often used for abrasive purposes.

Garnet species are found in many colors including red, orange, yellow, green, blue, purple, brown, black, pink and colorless. The rarest of these is the blue garnet, discovered in the late 1990s in Bekily, Madagascar. It is also found in parts of the United States, Russia and Turkey. Other varieties of color-changing garnets exist. In daylight, their color ranges from shades of green, beige, brown, gray, and blue, but in incandescent light, they appear a reddish or purplish/pink color. Because of their color changing quality, this kind of garnet is often mistaken for Alexandrite.

Garnet species' light transmission properties can range from the gemstone-quality transparent specimens to the opaque varieties used for industrial purposes as abrasives. The mineral's luster is categorized as vitreous (glass-like) or resinous (amber-like).

 

Aquamarine

The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white.

The name Aquamarine is from the Latin expression for seawater. Aquamarine is a member of the beryl family and is known for its delicate blue or blue green coloring, which accounts for its name. Aquamarine is the birthstone for March, and is is a popular stone with very good hardness and luster.

Aquamarines of the best quality are clear, transparent gems. Some gems can carry inclusions of long, hollow rods, a trademark of the beryl family. Aligned traces of foreign minerals, a rare feature, cause a cat's eye effect or star effect (asterism) with six rays in a vivid sheen. Cat's eye aquamarine and star aquamarine usually command premium prices. Hardness: 7.5 - 8 (Mohs scale)

 

Amethyst

Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- ("not") and μέθυστος methustos ("intoxicated"), a reference to the belief that the stone protected its owner from drunkenness. It is one of several forms of quartz.

Amethyst is the traditional birthstone for February, and occurs in primary hues from a light pinkish violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. The ideal grade is called "Deep Siberian" and has a primary purple hue of around 75–80%, with 15–20% blue and (depending on the light source) red secondary hues.

Green quartz is sometimes incorrectly called green amethyst, which is an actual misnomer and not an acceptable name for the material, the proper terminology being Prasiolite.

The color of amethyst has been demonstrated to result from substitution by irradiation of trivalent iron for silicon in the structure,in the presence of trace elements of large ionic radius,and, to a certain extent, the amethyst color can naturally result from displacement of transition elements even if the iron concentration is low. Natural amethyst is dichroic in reddish violet and bluish violet, but when heated, turns yellow-orange, yellow-brown, or dark brownish and may resemble citrine, but loses its dichroism, unlike genuine citrine. When partially heated, amethyst can result in ametrine.

Amethyst can fade in tone if overexposed to light sources and can be artificially darkened with adequate irradiation. The highest grade amethyst (called "Deep Russian") is exceptionally rare and therefore, when one is found, its value is dependent on the demand of collectors

 

Tanzanite

Tanzanite is the blue/purple variety of the mineral zoisite (a calcium aluminium hydroxy silicate) which was discovered in the Mererani Hills of Northern Tanzania in 1967, near the city of Arusha and Mount Kilimanjaro. It is used as a gemstone. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet and burgundy depending on crystal orientation. Tanzanite can also appear differently when viewed under alternate lighting conditions. The blues appear more evident when subjected to fluorescent light and the violet hues can be seen readily when viewed under incandescent illumination.

The Tanzanite is a rare gem. It is found mostly in the foothills of Mount Kilimanjaro. The mineral is named after Tanzania, the country in which it was discovered. The new system's color-grading scales divide tanzanite colors into a range of hues, between blue violet and violet blue. The normal primary and secondary hues in tanzanite are blue and purple, not violet. Purple is a modified spectral hue that lies halfway between red and blue. Tanzanite is a trichroic gemstone, meaning that light that enters the stone is divided into three sections, each containing a portion of the visible spectrum. After heating, tanzanite becomes dichroic. The dichroic colors are red and blue. The hue range of tanzanite is blue-purple to purple-blue.

 

Tourmaline

The Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors. The name comes from the Sinhalese word "Thuramali"  or "Thoramalliwhich applied to different gemstones found in Sri Lanka.

The most common species of tourmaline is schorl. It may account for 95% or more of all tourmaline in nature.

. The word tourmaline has two etymologies, both from the Sinhalese word turamali, meaning "stone attracting ash" (a reference to its pyroelectric properties) or according to other sources "mixed gemstones". the time it was not realised that schorl and tourmaline were the same mineral. Dravite

 

Tigers Eye

Tigers Eye is a chatoyant gemstone that is usually a metamorphic rock that is a golden to red-brown color, with a silky luster. A member of the quartz group, it is a classic example of pseudomorphous replacement by silica of fibrous crocidolite (blue asbestos). An incompletely silicified blue variant is called Hawk's eye.

The gems are usually cut en cabochon in order to best display their chatoyancy. Red stones are brought about through gentle heat treatment. Dark stones have had their colors improved and been artificially lightened using nitric acid treatments. Honey-colored stones have been used to imitate the much higher valued cat's eye chrysoberyl (cymophane), but the overall effect is unconvincing. Artificial fiberoptic glass is a common imitation of tiger's eye, and is produced in a wide range of colors. Tiger's Eye mostly comes from South Africa and East Asia.

 

Lapis

Lapis is a semi-precious stone that has been prized since antiquity for its intense blue color.Lapis lazuli was being mined in the Badakhshan province of Afghanistan as early as the 3rd millennium B.C.E.and there are sources that are found as far east as in the region around Lake Baikal in Siberia. Trade in the stone is ancient enough for lapis jewelry to have been found at Predynastic Egyptian and ancient Sumerian sites, and as lapis beads at neolithic burials in Mehrgarh, the Caucasus, and even as far from Afghanistan as Mauritania. The intense blue color is due to the presence of the S3- radical anion in the crystal.

 

Malachite

Malachite is a copper carbonate mineral. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms. Malachite often results from weathering of copper ores and is often found together with azurite goethite, and calcite. Except for its vibrant green color, the properties of malachite are similar to those of azurite and aggregates of the two minerals occur frequently. Malachite is more common than azurite and is typically associated with copper deposits around limestones, the source of the carbonate.3.5-4.0mohs scale.

 

Turquoise

Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times, turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market.

Even the finest of turquoise is fracturable, reaching a maximum hardness of just under 6, or slightly more than window glass. Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals and all of its properties are highly variable. Its crystal system is proven to be triclinic via X-ray diffraction testing. With lower hardness comes lower specific gravity (2.60–2.90) and greater porosity: These properties are dependent on grain size.

The luster of turquoise is typically waxy to subvitreous, and transparency is usually opaque, but may be semitranslucent in thin sections. Color is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue, and from a blue-green to a yellowish green. The blue is attributed to idiochromatic copper while the green may be the result of either iron impurities (replacing aluminium) or dehydration.

 

Carnelian

Carnelian (or cornelian) is a brownish-red mineral, which is commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker. (The difference is not rigidly defined, and the two names are often used interchangeably.) Both carnelian and sard are varieties of the silica mineral chalcedony colored by impurities of iron oxide.

The color can vary greatly, ranging from pale orange to an intense almost-black coloration. Carnelian was used widely during Roman times to make engraved gems for signet or seal rings for imprinting a seal with wax on correspondence or other important documents. Hot wax does not stick to carnelian. Sard was used for Assyrian cylinder seals, Egyptian and Phoenician scarabs, and early Greek and Etruscan gems. The Hebrew odem (translated sardius), the first stone in the High Priest's breastplate, was a red stone, probably sard but perhaps red jasper.

 

Quartz

Quartz Is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz, several of which are semi-precious gemstones. Throughout the world, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hardstone carvings.it is a 7.0 in the mohs scale,however it can be lower when other impurities are involved.

 

Jasper

A form of Chalcedony, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone. It can be highly polished and is used for vases, seals, and at one time for snuff boxes. When the colors are in stripes or bands, it is called striped or banded jasper.

Jaspilite is a banded iron formation rock that often has distinctive bands of jasper. Jasper is basically chert which owes its red color to iron inclusions. The jasper is, along with Heliotrope (bloodstone) an opaque rock of virtually any color stemming from the mineral content of the original sediments or ash.

Patterns arise during the consolidation process forming flow and depositional patterns in the original silica rich sediment or volcanic ash. Hydrothermal

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