A gemstone or gem (precious or semi-precious stone) is a piece of crystal (mineral), which, in cut and polished form. However, certain rocks(such as lapis lazuli) or organic materials that are not minerals (such as amber or jet), are also called as gemstones as well. Most gemstones are hard, but some are soft, because of their luster or other physical properties that have aesthetic value. Buying a gemstone can be a daunting task. It is an experience that requires trust, not only of our senses in judging what we can discern about the gem one is considering, but also the representations of the person selling the gem. Many factors set value. Some of them like weight are tangible; others like clarity, color or origin are not. Gemstones may be accompanied by a lab report listing the color, cut, clarity and weight. They may also contain a comment about treatments or origin. Certain gemstones such as ruby or sapphire can receive a premium in the market if they are believed to be from a particular country (origin). In lieu of an independent grading report, the seller may offer certain guarantees.Any material which has the three basic qualities of beauty, rarity and durability, called ‘B,R,D’ can be defined as a gemstone.
Beauty: This is a subjective property and is defined by the 4 “C’s”, Colour, Clarity, Cut and Carat (size).
A gemstone which exhibits an eye, star or change of colour would have an additional value.
Rarity: This is an important aspect. More the availability lesser the demand, lesser the availability higher the demand.
Durability: A gemstone must be durable enough to withstand daily wear and tear. A softer stone will get scratched more easily but not in a hard or tough stone.
Generally gemstones are classified between precious, semi-precious and organic. The precious stones are Diamond,Ruby,Sapphire and Emerald, etc. with all other gemstones being semi-precious. This distinction reflects the rarity of the respective stones, as well as their quality. All stones are classified by their colour, transparency and hardness. Gemstones are classified into different groups, species and varieties. For example, Ruby is the red variety of the species corundum, while any other colour of corundum is considered Sapphire. Other examples are the Emerald (green), Aquamarine (blue), Red-beryl (red), which is all varieties of the mineral species beryl. Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and lustre. Material or flaws within a stone may be present as inclusions. 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 use. Stones which are opaque or semi-opaque such as Opal, Turquoise, etc. are commonly cut as cabochons. These gems are designed to show the stone's colour or surface properties as in Opal and Star Sapphires.
The colour of any material is due to the nature of light itself. Daylight, often called white light, is actually all of the colours 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 colour. A Ruby appears red because it absorbs all the other colours of white light (green and blue), while reflecting the red. The same material can exhibit different colours. For example Ruby and Sapphire have the same chemical composition (both are corundum) but exhibit different colours. Even the same gemstone can occur in many different colours, Sapphires show different shades of blue and pink and "Fancy Sapphires" exhibit a whole range of other colours from yellow to orange-pink. This difference in colour 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 colours and leave the other colours unaffected. For example, Beryl, which is colourless 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.
Every gem listed on ratnabhandar.com has colour, clarity & cut rating with weight in carat, which makes easy for a customer to understand the quality of a gemstone.
.Gemstones are often treated to enhance the colour 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 colour is unstable and may revert to the original tone. Heat can improve gemstone colour 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 colour into the more desirable blue or enhance its existing blue colour to a purer blue. Nearly all Tanzanite is heated at low temperatures to remove brown undertones and give a more desirable blue/purple colour. A considerable portion of all Sapphire and Ruby is treated with a variety of heat treatments to improve both colour and clarity. Sapphires may be treated by several methods to enhance and improve their clarity and color. It is common practice to heat natural sapphires to improve or enhance color. This is done by heating the sapphires in furnaces to temperatures between 500 and 1800 °C for several hours, or by heating in a nitrogen-deficient atmosphere oven for seven days or more. Upon heating, the stone becomes more blue in color, but loses some of the rutile inclusions (silk). When high temperatures are used, the stone loses all silk (inclusions) and it becomes clear under magnification. Heat treatment was not commonly disclosed; by 1982 the heat treatment became a major issue. At that time, 95% of all the world's sapphires were being heated to enhance their natural color. This issue appeared as a front page story in the Wall Street Journal on August 29, 1984 in an article by Bill Richards, Carats and Schticks: Sapphire Marketer Upsets. The Gem Industry Diffusion treatments are used to add impurities to the sapphire to enhance color. Typically beryllium is diffused into a sapphire under very high heat, just below the melting point of the sapphire. Initially (c. 2000) orange sapphires were created, although now the process has been advanced and many colors of sapphire are often treated with beryllium. When jewellery 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 jewellery 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 is another proses, this does not cite any references or sources. Virtually all Blue Topaz, both the lighter and the darker blue shades such as "London" blue, has been irradiated to change the colour from white to blue. Most greened Quartz (Oro Verde) is also irradiated to achieve the yellow-green colour. Emeralds containing natural fissures are sometimes filled with wax or oil to disguise them. This wax or oil is also coloured to make the emerald appear of better colour as well as clarity. Turquoise is also commonly treated in a similar manner. Fracture filling has been in use with different gemstones such as Diamonds, Emeralds and Sapphires. In 2006 "glass filled Rubies" received publicity. Rubies 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.
Enhancements are treatments, other than cutting or polishing, which are performed on natural gemstones to improve their durability, availability, or appearance. By enhancing a gemstone, its natural colour and stunning beauty is released, allowing it to truly sparkle. There are several enhancement processes, some permanent, and some temporary. It is important to remember that the enhancements whether heat, irradiation, diffusion, dye, coating, filling, bleaching, oiling or laser are utilized to positively alter the gemstone. Gemstone enhancement is a common practice throughout the jewellery industry. Many gemstones today are treated or enhanced in various ways to improve colour and (sometimes) clarity. It is important to understand why some gems are treated. The supply of high quality gemstones is falling as mines are being depleted. At the same time, consumer interest in gemstones is increasing. These trends lead to a scarcity of fine gemstones, and a corresponding increase in prices. Un-heated natural stones are somewhat rare and will often be sold accompanied by a certificate from an independent gemmological laboratory attesting to "no evidence of heat treatment".
The demand of good quality gemstones is developing the techniques of certain treatments to maximize the colour and clarity of the scarce gemstone from the remaining gem mines. The most common of these techniques is heat treatment, which improves gemstone’s colour through the use of high temperatures, mimicking the effects of nature as gemstones are formed through heat and pressure. Other kinds of treatment include fracture filling, and the addition of certain chemicals such as beryllium to the heating process. These treatments significantly improve the appearance of many gemstones, but they also affect the value of the stone. A treated stone is always less valuable than a similar untreated stone. But most stones that are routinely treated - such as ruby and sapphire - are now very rare in untreated form, which means that the untreated stones fetch a market price out of the reach of most consumers. The customer can get information of treatment from the comments available on lab testing certificates, but the authenticity of testing lab should be verified. However, if you would prefer to buy an untreated stone, there are still many choices but always purchase it from ratnabhandar.com. In every gemstone purchased from ratnabhandar.com, customer must know whether it is heated or unheated and treated or untreated.
Once you've invested in a fine gemstone, proper care will help keep it looking new and vibrant for many years. Most gemstones are very durable and require only occasional cleaning. But some gems require special care, since they are sensitive to temperature change, excessive light exposure or chemicals. Some gems, such as Opal, gomed, emerald, etc. have significant water content, and should be protected from dry air.
These are some common natural stones:
Amethyst is a violet or purple variety of quartz and owes its violet color to irradiation, iron impurities (in some cases in conjunction with transition element impurities), and the presence of trace elements, which result in complex crystal lattice substitutions. The hardness of the mineral is the same as quartz, thus it is suitable for use in jewelry.
Apatite is infrequently used as a gemstone. Transparent stones of clean color have been faceted, and chatoyant specimens have been cabochon cut. If crystals of rutile have grown in the crystal of apatite, in the right light the cut stone displays a cat's eye effect. Major sources for gem apatite are Brazil, Burma, and Mexico. Other sources include Canada, Czech-republic, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the United States.
It is a blue or cyan variety of Beryl. It occurs at most localities which yield ordinary Beryl. The gem-gravel placer deposits of Sri Lanka contain Aquamarine. Clear yellow Beryl, such as that occurring in Brazil, is sometimes called Aquamarine Chrysolite. The deep blue version of aquamarine is called maxixe. Maxixe is commonly found in the country of Medagascar. Its colour fades to white when exposed to sunlight or is subjected to heat treatment, though the colour returns with irradiation.
Citrine is a variety of quartz whose colour ranges from a pale yellow to brown due to ferric impurities. Natural Citrines are rare; most commercial Citrines are heat-treated amethysts or smoky quartzes. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a natural Citrine's cloudy or Smokey appearance. It is nearly impossible to tell cut Citrine from yellow topaz visually, but they differ in hardness. Brazil is the leading producer of Citrine, with much of its production coming from the state of Rio Grande do Sul. The name is derived from Latin Citrina which means "yellow" and is also the origin of the word "citron." Sometimes Citrine and Amethyst can be found together in the same crystal, which is then referred to as Ametrine.
The hard skeleton of red Coral branches is naturally matte, but can be polished to a glassy shine. It exhibits a range of warm reddish pink colours from pale pink to deep red; the word Coral is also used to name such colours. Owing to its intense and permanent coloration and glossiness, precious coral skeletons have been harvested since antiquity for decorative use.
Pure Carbon, Diamond is one of the oldest minerals in the Universe. Diamond is one of the best-known and most sought-after gemstones. The hardness of Diamond and its high dispersion of light – giving the Diamond its characteristic "fire" – make it useful for industrial applications and desirable as jewellery. Diamonds are such a highly traded commodity that multiple organizations have been created for grading and certifying them based on the four Cs, which are colour, cut, clarity, and carat. Other characteristics, such as presence or lack of fluorescence, also affect the desirability and thus the value of a diamond used for jewellery.
Emerald is one of the most valuable gems, prized throughout history. It is considered one of the “big three” in the industry – ruby, emerald, sapphire. Color: Very strongly bluish green, very slightly bluish green, green and slightly yellowish green. Clarity: Type III usually has eye visible inclusions. Cut: Some native cuts may be found (gems cut at the mine location without high regard to skill in cutting). However, well-cut stones are available. Carat weight: Stones weighing more than 8 carats are rare in finer quality. In commercial qualities, stones are available in all sizes up to 20 carats or even larger may be encountered. Reference Data: Refractive Index: 1.577-1.583, Specific Gravity: 2.72 Common Treatments: Nearly all emeralds are oiled with a variety of oils, some with resins added. Filling of emeralds may also take place. These treatments help to hide the natural fissures within emeralds which is a common feature of their growth in nature.
Emerald is one of the most valuable gems, prized throughout history. Emerald refers to green beryl, coloured by trace amounts of chromium and sometimes vanadium. Most Emeralds are highly included, so their brittleness (resistance to breakage) is classified as generally poor. Emeralds in antiquity were mined by the Egyptians and in Austria, as well as Swat in northern Pakistan. A rare type of Emerald known as a trapiche emerald is occasionally found in the mines of Colombia. A Trapiche Emerald exhibits a "star" pattern; it has ray like spokes of dark carbon impurities that give the Emerald a six-pointed radial pattern. Colombian Emeralds are generally the most prized due to their transparency and fire. Some of the rarest Emeralds come from three main Emerald mining areas in Colombia. Fine Emeralds are also found in other countries, such as Zambia, Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia. In the US, emeralds can be found in Hiddenite, North Carolina. In 1998, emeralds were discovered in the Yukon.
Garnet species are found in many colours including red, orange, yellow, green, purple, brown, blue, black, pink and colourless. 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, Kenya, Tanzania, and Turkey. It changes colour from blue-green in the daylight to purple in incandescent light, as a result of the relatively high amounts of vanadium. Other varieties of colour-changing garnets exist. In daylight, their colour ranges from shades of green, beige, brown, grey, and blue, but in incandescent light, they appear a reddish or purplish/pink colour. Because of their colour-changing quality, this kind of garnet is often mistaken for Alexandrite.
Exhibiting strong pleochroism, it appears different colours when viewed from different angles. As the transparent variety iolite, it is often used as a gemstone. Gem quality iolite varies in colour from Sapphire blue to blue violet to yellowish grey to light blue as the light angle changes. Iolite is sometimes used as an inexpensive substitute for Sapphire. It is much softer than Sapphires and is abundantly found in Australia (Northern Territory), Brazil, Burma, Canada (Yellowknife area of the Northwest Territories), India, Madagascar, Namibia, Sri Lanka, Tanzania and the United States (Connecticut). The largest Iolite crystal found weighed more than 24,000 carats, and was discovered in Wyoming, US.
Kyanite is a member of the alum inosilicate series, which also includes the polymorph andalusite and the polymorph sillimenite. Kyanite is strongly anisotropic, in that its hardness varies depending on its crystallographic direction. In kyanite, this anisotropism can be considered an identifying characteristic. Kyanite has been used as a semiprecious gemstone. Color varieties include recently discovered orange kyanite from Tanzania. The orange color is due to inclusion of small amounts of manganese in the structure.
Called the 'stone of rulers,' in some ancient kingdoms, lapis was forbidden to commoners, and worn only by royalty. Lapis lazuli is found in limestone in the Kokcha River valley of Badakhshan province in north-eastern Afghanistan, where the Sar-e-Sang mine deposits have been worked for more than 6,000 years. Afghanistan was the source of lapis for the ancient Egyptian and Mesopotamian civilizations, as well as the later Greeks and Romans. Ancient Egyptians obtained this material through trade from Afghanistan. During the height of the Indus valley civilization about 2000 BC, the Hardpan colony now known as Shortugai was established near the lapis mines. In addition to the Afghan deposits, lapis is also extracted in the Andes (near Ovalle, Chile); and to the west of Lake Baikal in Siberia, Russia, at the Tultui Lazurite deposit. It is mined in smaller amounts in Angola, Argentina, Burma, Pakistan, Canada, Italy, India, and in the USA in California and Colorado.
Moonstone is composed of two feldspar species, orthoclase and albite. The two species are intermingled. Then, as the newly formed mineral cools, the intergrowth of orthoclase and albite separates into stacked, alternating layers. When light falls between these thin, flat layers, it scatters in many directions producing the phenomenon called adularescence. Deposits of moonstone occur in Australia, the Austrian Alps, Mexico, Madagascar, Burma, Norway, Poland, India, Sri Lanka and The United States. It is currently the state gem for Florida, to commemorate the Moon landings, which took off from Florida. Despite it being the state gem, it does not naturally occur in Florida, or on the Moon.
Opal is the national gemstone of Australia. Australian opal has often been cited as accounting for 95-97% of the world's supply of precious opal, with the state of South Australia accounting for 80% of the world's supply. The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colours. Precious opal ranges from clear through white, grey, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the rarest, whereas white and greens are the most common. It varies in optical density from opaque to semi-transparent.
Natural pearls are nearly 100% calcium carbonate and conchiolin. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters a bivalve mollusk and settles inside the shell. The mollusk, irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare.
Cultured pearls can be distinguished from natural pearls by X-ray examination. Nucleated cultured pearls are often 'preformed' as they tend to follow the shape of the implanted shell bead nucleus. After a bead is inserted into the oyster, it secretes a few layers of nacre around the bead; the resulting cultured pearl can then be harvested in as few as six months. When a cultured pearl with a bead nucleas is X-rayed, it reveals a different structure to that of a natural pearl (see diagram). A beaded cultured pearl shows a solid center with no concentric growth rings, whereas a natural pearl shows a series of concentric growth rings. A beadless cultured pearl (whether of freshwater or saltwater origin) may show growth rings, but also a complex central cavity, witness of the first precipitation of the young pearl sac.
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. Ruby is considered one of the four precious stones, together with sapphire, emerald and diamond. Ruby is generally considered the most valuable of the colored gemstones when priced per carat for exceptional quality gems. It is considered one of the “big three” in the industry. Color: Rubies vary in color from orangy red, red slightly purplish red, strongly purplish red, to red. Prices of rubies are primarily determined by color. The brightest and most valuable "red" called blood-red, commands a large 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. All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes. Clarity: Type II May be eye clean with minor inclusions visible under magnification. Cut: Cut and carat (weight) are also an important factor in determining the price.Some native cuts may be found (gems cut at the mine location without high regard to skill in cutting). However, well-cut stones are available. Carat weight: Stones weighing more than 5 carats in finer qualities are very rare. In commercial grades, stones are available from in all sizes up to 10 carats. Reference Data: Refractive Index: 1.762-1.770, Specific Gravity: 4.00 Common Treatments: Most rubies are heat treated to improve color. Some may also be heated in the presence of flux which can leave residue within the ruby, known as flux healing. Another method of filling fissures uses lead glass and leaves this residue inside the gemstone.
Usually the rough stone is heated before cutting. Some rubies show a three-point or six-point asterism or "star". These rubies are cut into cabochons to display the effect properly. Asterisms are best visible with a single-light source, and move across the stone as the light moves or the stone is rotated. Such effects occur when light is reflected off the "silk" (the structurally oriented rutile needle inclusions) in a certain way. This is one example where inclusions increase the value of a gemstone. Furthermore, rubies can show color changes—though this occurs very rarely—as well as chatoyancy or the "cat's eye" effect.
The Moqok Valley in Upper Myanmar (Burma) was for centuries the world's main source for rubies. That region has produced some of the finest rubies ever mined, but in recent years very few good rubies have been found there. The very best color in Myanmar rubies is sometimes described as "pigeon's blood." In central Myanmar, the area of Mong Hsu began producing rubies during the 1990s and rapidly became the world's main ruby mining area. The most recently found ruby deposit in Myanmar is in Namya (Namyazeik) located in the northern state of Kachin. Rubies have historically been mined in Thailand, the Pailin and Samlout District of Cambodia, Burma, India, Afghanistan, Australia, Namibia, Colombia, Japan, Scotland, Brazil and in Pakistan. In Sri Lanka, lighter shades of rubies (often "pink sapphires") are more commonly found. After the Second World War ruby deposits were found in Tanzania, Madagascar, Vietnam, Nepal, Tajikistan, and Pakistan. A few rubies have been found in the U.S. states of Montana, North Carolina, South Carolina and Wyoming. While searching for luminous schist’s in Wyoming, geologist Dan Hausel noted an association of vermiculite with ruby and sapphire and located six previously undocumented deposits. More recently, large ruby deposits have been found under the receding ice shelf of Greenland. Republic of Macedonia is the only country in mainland Europe to have naturally occurring rubies. They can mainly be found around the city of Prilep. Macedonian ruby has a unique raspberry color. The ruby is also included on the Macedonian Coat of Arms. In 2002 rubies were found in the Waseges River area of Kenya. There are reports of a large deposit of rubies found in 2009 in Mozambique, in Nanhumbir in the Cabo Delgado district of Montepuez. Spinel, another red gemstone, is sometimes found along with rubies in the same gem gravel or marble. Red spinel may be mistaken for ruby by those lacking experience with gems. However, the finest red spinels can have a value approaching that of the average ruby.
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 a pinkish orange variety. Although blue is their most well-known color, sapphires may also be colorless and they are found in many colors including shades of gray and black. It is a gemstone variety of the mineral corundum, an aluminium oxide. Trace amounts of elements such as iron, titanium, chromium, copper, or magnesium can give corundum respectively blue, yellow, purple, orange, or green color. Chromium impurities in corundum yield pink or red tint, the latter being called ruby. It is considered one of the “big three” in the industry – ruby, emerald, sapphire. Sapphires can be found in a variety of colors in each of the seven primary hues. However, blue is the most common, most desired, and most expensive. Clarity: Type May be eye clean with minor inclusions visible under magnification. Cut: Some native cuts may be found (gems cut at the mine location without high regard to skill in cutting). However, well-cut stones are available. Carat weight: Stones weighing more than 20 carats is rare in finer qualities. In lower grades very large sizes are available. Reference Data: Refractive Index: 1.762-1.770, Specific Gravity: 4.00 Treatment: Heat is very commonly used to improve the color of sapphires.Because of the remarkable hardness of sapphires—9 on the Mohs scale (the third hardest mineral, right behind diamond at 10 and moissanite at 9.25)—and of aluminium oxide in general. 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, China (Shondong), Madagascar, East Africa, and in North America in a few locations, mostly in Montana. Sapphire and rubies are often found in the same geographic environment, but one of the gems is usually more abundant in any of the sites. Violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative. Blue sapphires with up to 15% violet or purple are generally said to be of fine quality. Blue sapphires with any amount of green as a secondary. Gray reduces the saturation or brightness of the hue, and therefore has a distinctly negative effect. 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 toward the red of rubies. In the United States, minimum color saturation must be met to be called a ruby, otherwise the stone is referred to as a pink sapphire. Sapphires also occur in shades of orange and brown. Colorless sapphires are sometimes used as diamond substitutes in jewellery. Natural padparadscha (pinkish orange) sapphires often draw higher prices than many of even the finest blue sapphires. Padparadscha is a delicate light to medium toned pink-orange to orange-pink hue corundum, originally found in Sri Lanka, but also found in deposits in Vietnam and parts of East Africa. Padparadscha sapphires are rare; the rarest of all is the totally natural variety, with no sign of artificial treatment. The name is derived from the Sanskrit "padmaranga" (padma = lotus; ranga = color), a color akin to the lotus flower (Nelumbonucifera‘Speciosa’). A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism; red stones are known as "star rubies". The inclusion is often the mineral rutile, a mineral composed primarily of titanium dioxide. Occasionally, twelve-rayed stars are found. The 423-carat (84.6 g) Logan sapphire in the National Museum of Natural History, in Washington, D.C., is one of the largest faceted gem-quality blue sapphires in existence. The Black Star of Queensland, the largest gem-quality star sapphire in the world, weighs 733 carats. The Star of India (mined in Sri Lanka) (weighing 563.4 carats) is thought to be the second-largest star sapphire (the largest blue), and is currently on display at the American Museum of Natural History in New York City. The 182-carat Star of Bombay, (mined in Sri Lanka), located in the National Museum of Natural History, in Washington, D.C., is another example of a large blue star sapphire. The sapphire deposits of Kashmir are still well known in the gem industry, despite the fact that the peak production from this area mostly took place in a relatively short period at the end of the nineteenth and early twentieth centuries. Kashmir-origin contributes meaningfully to the value of a sapphire, and most corundum of Kashmir origin can be readily identified by its characteristic silky appearance and exceptional hue. At present, the world record price-per-carat for sapphire at auction was achieved by a sapphire from Kashmir in a ring, which sold for $180,731 per carat (more than $5 million in total, including buyer's premium) in April 2014. The value of a star sapphire depends not only on the weight of the stone, but also the body color, visibility, and intensity of the asterism. A rare variety of natural sapphire, known as color-change sapphire, exhibits different colors in different light. Color change sapphires are blue in outdoor light and purple under incandescent indoor light, or green to gray-green in daylight and pink to reddish-violet in incandescent light. Color change sapphires come from a variety of locations, including Thailand and Tanzania. The color-change effect is caused by the interaction of the sapphire, which absorbs specific wavelengths of light, and the light-source, whose spectral output varies depending upon the illuminate. Transition-metal impurities in the sapphire, such as chromium and vanadium, are responsible for the color change. Corundum that contains ~0.01% of titanium is colorless. If trace amounts of iron are present, a very pale yellow to green color may be seen. However, if both titanium and iron impurities are present together, and in the correct valence states, the result is a deep-blue color. Intervalence charge transfer is a process that produces a strong colored appearance at a low percentage of impurity. While at least 1% chromium must be present in corundum before the deep red ruby color is seen, sapphire blue is apparent with the presence of only 0.01% of titanium and iron.
The great imposter of the gemstone world' plays a starring role in the British Crown Jewels. The transparent red spinels were called spinel-rubies or balas rubies. In the past, before the arrival of modern science, spinels and rubies were equally known as rubies. After the 18th century the word ruby was only used for the red gem variety of the mineral corundum and the word spinel became used. "Balas" is derived from Balascia, the ancient name for Badakhshan, a region in central Asia situated in the upper valley of the Kokcha River, one of the principal tributaries of the Oxus River. The Badakshan Province was for centuries the main source for red and pink spinels.
Spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestone’s of the Badakshan Province in modern day Afganisthan and of Mogok in Burma. Recently gem quality spinels were also found in the marbles of Luc Yen (Vietnam), Mahenge and Matombo (Tanzania), Tsavo (Kenya) and in the gravels of Tunduru (Tanzania) and Ilakaka (Madagascar). Spinel is found as a metamorphic, and also as a primary mineral in rare mafic igneous rocks; in these igneous rocks, the magmas are relatively deficient in alkalis relative to aluminium, and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel and ruby are often found together.
Brightly colored Sri Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy a demand for curiosities and gems. At the time it was not realised that schorl and tourmaline were the same mineral (it was only about 1703 that it was discovered that some colored gems weren't zircons). Tourmaline was sometimes called the "Ceylonese [Sri Lankan] Magnet" because it could attract and then repel hot ashes due to its pyroelectric properties. Tourmalines were used by chemists in the 19th century to polarize light by shining rays onto a cut and polished surface of the gem. The most common species of tourmaline is schorl, the sodium iron (divalent) end member of the group. 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 substance has been known by many names, but the word turquoise, which dates to the 16th century, is derived from an Old French word for "Turkish", because the mineral was first brought to Europe from Turkey. Even the finest of turquoise is fracturable, reaching a maximum hardness of just under 6, or slightly more than window glass. The lustre of turquoise is typically waxy to sub vitreous, and transparency is usually opaque, but may be semi translucent in thin sections. Colour 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. Under long wave ultra violet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under short wave ultra violet and X-rays. Despite its low hardness relative to other gems, turquoise takes a good polish. For at least 2,000 years, Iran, known before as Persia in the West, has remained an important source of turquoise. In Iranian architecture, the blue turquoise was used to cover the domes of the Iranian palaces because its intense blue colour was also a symbol of heaven on earth. Since at least the First Dynasty (3000 BCE), and possibly before then, turquoise was used by the Egyptians and was mined by them in the Sinai Peninsula, called "Country of Turquoise" by the native Monitu. Other notable localities include: Afghanistan; Australia (Victoria and Queensland); north India; northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan. The Persian style and use of turquoise was later brought to India following the establishment of the Mughal Empire there, its influence seen in high purity gold jewellery (together with ruby and diamond) and in such buildings as the Taj Mahal. In many cultures of the Old and New Worlds, this gemstone has been esteemed for thousands of years as a holy stone, a bringer of good fortune or a talisman. It really does have the right to be called a 'gemstone of the peoples'. The oldest evidence for this claim was found in Ancient Egypt, where grave furnishings with turquoise inlay were discovered, dating from approximately 3000 BCE. Hardness and richness of colour are two of the major factors in determining the value of turquoise.
Zircon is ubiquitous in the crust of Earth. It occurs as a common accessory mineral in igneous rocks (as primary crystallization products), in metamorphic rocks and as detrital grains in sedimentary rocks Large zircon crystals are rare. Their average size in granite rocks is about 0.1–0.3 mm, but they can also grow to sizes of several centimetres, especially in mafic pegmatites and carbonatites
Because of their uranium and thorium content, some zircons undergo metamictization. Connected to internal radiation damage, these processes partially disrupt the crystal structure and partly explain the highly variable properties of zircon. As zircon becomes more and more modified by internal radiation damage, the density decreases, the crystal structure is compromised, and the color changes.
Zircon occurs in many colors, including reddish brown, yellow, green, blue, gray and colorless. The color of zircons can sometimes be changed by heat treatment. Common brown zircons can be transformed into colorless and blue zircons by heating to 800 to 1000 °C. In geological settings, the development of pink, red, and purple zircon occurs after hundreds of millions of years, if the crystal has sufficient trace elements to produce color centres. Color in this red or pink series is annealed in geological conditions above the temperature about 350 °C. Zircon is mainly consumed as an opacifier, and has been known to be used in the decorative ceramics industry. It is also the principal precursor not only to metallic zirconium, although this application is small, but also to all compounds of zirconium including zirconium dioxide (ZrO2), one of the most refractory materials known.
Cat’s eye gemstones, with a yellow colored light passing through the center, are ideal for any piece of jewellery, but there is more to these marvels than their distinctly elegant radiance. Although predominantly found in the colors of black, honey, and yellowish-green, nowadays, different colors of cat stones are available. Primarily found in India, Sri Lanka, Burma, Tanzania, Brazil and Russia. Translucent yellowish chatoyant chrysoberyl is called cymophane or cat's eye. Cymophane has its derivation also from the Greek words meaning 'wave' and 'appearance', in reference to the haziness that visually distorts what would normally be viewed as a well defined surface of a cabochon. This effect may be combined with a cat eye effect. In this variety, microscopic tube like cavities or needle like inclusions of rutile occur in an orientation parallel to the c-axis, producing a chatoyant effect visible as a single ray of light passing across the crystal. This effect is best seen in gemstones cut in cabochon form perpendicular to the c-axis. The color in yellow chrysoberyl is due to Fe3+ impurities.
Although other minerals such as tourmaline, scapolite, corundum, spinel and quartz can form "cat's eye" stones similar in appearance to cymophane, the jewellery industry designates these stones as "quartz cat's eyes", or "ruby cat's eyes" and only chrysoberyl can be referred to as "cat's eye" with no other designation.
Gems lacking the silky inclusions required to produce the cat's eye effect are usually faceted. An alexandrite cat's eye is a chrysoberyl cat's eye that changes color. "Milk and honey" is a term commonly used to describe the color of the best cat's eyes. The effect refers to the sharp milky ray of white light normally crossing the cabochon as a center line along its length and overlying the honey-colored background. The honey color is considered to be top-grade by many gemologists but the lemon yellow colors are also popular and attractive. Cat's eye material is found as a small percentage of the overall chrysoberyl production wherever chrysoberyl is found.
Cat's eye really became popular by the end of the 19th century when the Duke of Connaught gave a ring with a cat's eye as an engagement token; this was sufficient to make the stone more popular and increase its value greatly. Until that time, cat's eye had predominantly been present in gem and mineral collections. The increased demand in turn created an intensified search for it in Sri Lanka.
December: Zircon (now tanzanite on some lists)