JEWELRY GUIDE



art guide
Last Updated: October 2009

SEMIPRECIOUS GEMS

In addition to precious gems such as diamonds, emeralds, sapphires and rubies, there are several other gems that can greatly enhance any piece of jewellery. These jewels are not as valuable as the precious gems per se, but an exceptional semiprecious gemstone can sometimes command a price higher than a normal sample of a precious gem. Available in a wide array of shapes, sizes and colours, some of the semiprecious gems of worth are spinel, turquoise, jade, open, moonstone, tourmaline, garnet, chalcedony, alexandrite and amethyst.

Spinel

Usually found in brilliant shades of red, the spinel has held an important place in the spectrum of coloured gemstones for centuries, largely because of its close physical and chemical resemblance to the ruby. Rubies, a red variety of the mineral corundum, are made of aluminium oxide, while spinels consist of magnesium aluminium oxide. Both stones attain their red colour due to the presence of chromium. And while the spinel is not as hard as the ruby, it's rating of 8 on the Mohs scale still makes it one of the hardest minerals found in nature.

Because of its strong similarity to ruby, spinel has often been both confused and substituted for rubies. The Black Prince's Ruby, which is not a ruby at all, is perhaps the most famous spinel ever known. This 170 carat red spinel is set in the Imperial State Crown of England in the British Crown Jewels, and was even worn by King Henry V in his battle helmet.

Although spinels are not as expensive as rubies, they are valuable gems in their own right. The most commonly found spinels are in shades of pink or red, but they can also sometimes occur as green, blue, purple, brown, and black. Spinels were historically called Balas Rubies after the Badakshan region in northern Afghanistan, which was famed for gem production in the Middle Ages. The stone has traditionally been mined in Burma, particularly in the Mogok region that has produced famed and brilliant rubies. Today spinels are also mined in Sri Lanka, Thailand, Brazil, Afghanistan, Tanzania, Tajikistan and Cambodia.

Turquoise

Rarely are stones surrounded by as much superstition across cultures as turquoise has been. In ancient Persia, turquoise was a symbol of life and vivacity. Sky blue turquoise was worn as jewels to protect against unnatural death, and it was considered a sign of impending tragedy if it changed colour. In Asia, turquoise was worn to protect against the 'evil eye'. Mexicans considered turquoise to be holy.

The bright colour of the stone is said to make the wearer confident, and in modern gemstone therapy, people suffering from depression are often advised to wear turquoise jewellery. Turquoise is also said to symbolise fidelity and dependability in relationships.

A copper aluminium phosphate, turquoise is often found in crevices in volcanic rock and in regions where there is a high concentration of copper. The most famous deposits are in the USA, Mexico, Israel, Iran, Afghanistan and China. Natural turquoise varies in colour from sky blue to grey green, but prized turquoise of the best quality is a sharper blue than green. The stone derives its blue colour from copper and its green from iron and chrome. Turquoise may also contain veins or blotches, which may be brown, light grey or black and are known as matrix or spider webs. Turquoise of an exceptional blue colour is valued with or without a matrix. Turquoise is rarely faceted as it is opaque. Instead, it is usually cut into cabochons.

Turquoise is also sensitive to the elements, and may discolour over time. To prevent discolouration, it can be treated with wax, which hardens the stone and stabilises it's colour.

Jade

Jade consists of two minerals, nephrite and jadeite, which were only distinguished from one another at the beginning of the 19th century. Pure jadeite is white, deriving its colour from trace impurities. Although it can be found in various colours, the most popular and valuable are shades of green, such as dark green and emerald green. Nephrite, on the other hand, is found mainly in shades of green, the most famous known as spinach green.

While they may differ in colour, nephrite and jadeite have similar characteristics. Both are tough and also often have veins or streaks, which are not necessarily considered defects and often enhance the beauty and value of the stone. The value of jade is generally determined by its colour, clarity and transparency. Green jade is the most sought after, and jadeite is more valuable than nephrite because it is available in more vibrant shades of green and is scarcer.

The Maw-sit-sit, a rare, deep green jade with streaks of black, is peculiar in the Tawmaw region of Myanmar where jade is mined. It is a popular and beautiful variety of jade with properties similar to that of jadeite. In addition to Myanmar, other sources of jade are Russia, Canada, New Zealand, China, USA, and Guatemala.

Jade is an opaque stone and is thus usually fashioned into cabochons or beads. Jade bangles and rings are also extremely popular items of jewellery. The stone has held special significance for the people of China since 3000 B.C., when it was referred to as yu or royal gem. Till today, the Chinese believe that jade will shield them from harm.

Opal

The word opal comes from the Latin word opalus and the Sanskrit word upala both meaning 'precious stone'. The inherent beauty in the opal lies in the spectacular array of colours or fire that is often visible in a single stone. An ideal opal is one that exhibits a broad variety of colours on the surface of the stone.

Opals range from transparent to translucent and may be white, colourless, pale yellow, red, grey, or black. Diffraction can cause a play of colours to appear on the surface in a phenomenon known as opalescence: the colour of the stone changes in flashes when the angle at which it is viewed is altered. Opals that display this phenomenon are frequently referred to as precious opals; the rest are referred to as common opals.

The most sought after opals are black opals, which have either dark blue, dark green, or black backgrounds and exhibit a strong play of colours. Opals known as white opals have a light tinted basic colour and also exhibit a play of colours. These opals are usually translucent and are cut into cabochons. A type of opal known as the Mexican fire opal has a basic orange hue and is usually transparent, and therefore may be faceted. If these opals display opalescence, they are known as Precious Fire Opals.

The value of an opal is determined by the intensity and distribution of its play of colour, its size, shape, and weight. The best and most important source of opals in the world since 1872 has been Australia, which has produced several black opals as well as those of other colours. Other global sources of opal are Mexico, Honduras, USA, the Czech Republic and Slovakia.

Moonstone

Approximately two-thirds of all the rocks on Earth are of the mineral group feldspar, which includes the iridescent moonstone. The moonstone is of the feldspar variety adularia and is also known as selenite, derived from 'selene', meaning moon, in Greek.

The defining trait of the moonstone is its play of light, which is also known as adularescence. Caused by thin layers of feldspar in the stone, adularescence refers to the reflective phenomenon caused by the scattering of incident rays of light. The most valuable moonstones are blue with an almost-transparent background and are usually found in Sri Lanka. Since these are becoming increasingly rare, blue moonstones command a high price. Indian moonstones may be beige, brown, green, orange, champagne coloured, or smoky. Moonstones are also found in USA, Brazil, Australia, Myanmar and Madagascar.

A variety of feldspar known as the rainbow moonstone is also found in India and Madagascar. In a rainbow moonstone, the adularescent sheen ranges from pink to purple to blue to peach to yellow. A single rainbow moonstone may exhibit all these colours.

Moonstones are usually cut as cabochons. The most important aspect to be determined while cutting is the ideal height of the stone in order to facilitate maximum adularescence or play of light. The factors that determine the value of moonstones are their sheen, clarity and colour. The value of a moonstone increases with its transparency.

Care must be taken of moonstones, as they are relatively soft gemstones with a hardness of 6 on the Mohs scale, and are susceptible to pressure and scratches. There are no known treatments to enhance the quality of a moonstone.

Tourmaline

Tourmalines are gems that can be found in a great variety of colours. In fact, the word tourmaline is derived form the Sinhalese word tura mali, which means 'mixed stone'. Tourmaline is not a single mineral but a group of minerals related by the close similarity of their physical and chemical properties.

Tourmalines are mixed crystals of aluminium boron silicate, and even slight changes in their chemical composition cause completely different colours. There are tourmalines in single colours, while some may have two colours in a single stone. Certain tourmalines may even change colour when the light source changes from natural to artificial.

Different coloured tourmalines are known by different names. Tourmalines that are red in natural and artificial light are known as rubelites; red tourmalines that turn pink when the light changes are called a pink tourmalines; blue tourmalines are known as indicolites; yellowish brown tourmalines are known as dravites; green tourmalines are known as verdelites; and black tourmalines are known as schorl. Tourmalines with two colours are bicoloured tourmalines, while those with more are known as multicoloured tourmalines. A particularly attractive type of tourmaline is known as the watermelon tourmaline because it has a red centre and is surrounded by a layer of green. When cut into a gem, these tourmalines are green on one side and red on the other.

Tourmalines are found all over the world, with the major mining areas in Brazil, Sri Lanka, Nigeria, Zimbabwe, Kenya, Tanzania, Mozambique, Madagascar, USA, Pakistan and Afghanistan. Although they are so abundantly available, tourmalines of exceptional colour and quality are rare. The value of a tourmaline is determined by its colour, undertones, and clarity.

Garnet

Garnet is a term used for a group of six minerals with similar characteristics: pyrope, almandine, grossularite, spessartite, andradite and uvarovite. Although red garnets are the most popular and ubiquitous in jewellery, garnets are available in several colours, including green, yellow and orange. Blue is the only colour in which garnets are not found.

The most typical images of a garnet are those associated with pyrope and almandine garnets, which are red. Pyropes have a deep, blood red colour with a brown tinge and were much sought after in the 18th and 19th centuries. They are almost entirely free of inclusions. While pyropes found in nature are small stones, almandines are larger. Named after Alabanda, an ancient city, almandines have a chemical composition similar to that of pyropes, but the two differ significantly in size. Almandines are darker than pyropes and are often used in jewellery after hollowing out the stone to lighten its colour. Rhodolite, a mixture of pyrope and almandine, is another popular variety of red garnet.

Among garnets of other colours is spessartite, named after a region in Germany where it was discovered. Spessartites are orange and are often known as mandarin garnets. Among the varieties of green garnets are grossularite, demantoid, and tsavorite, which can be found in Mali, Tanzania, Russia, and Namibia.

Garnets are ideal for use in jewellery because of their high refractive index, durability, transparency, and colour range.

Chalcedony � Agate and Onyx

Quartz is the most commonly available mineral, and is found in almost all rock types in a variety of colours and forms. Quartz that is formed not of one single crystal but a number of finely grained microcrystals is known as chalcedony, the most important types of which are agate and onyx.

Agate is a multicoloured variety of chalcedony. It occurs in concentric layers and in a wide variety of colours and textures with or without banding lines. There are various types of agate based on their appearance, colours and texture, such as blue lace agate, Botswana agate, crazy lace agate, fire agate, and moss agate. A refined agate stone is usually polished, as unpolished agate is too dull to be used in jewellery. In ancient times, agate was an extremely valued amulet believed to quench thirst and protect from fevers.

Onyx is a variety of agate where the banding lines are straight and parallel, and the bands are consistent in size. It is usually black with white lines or bands, although it may also be found as a pure black stone, and is typically referred to as black onyx. Onyx is completely opaque and is therefore usually cut into cabochons or beads. Originally, almost all varieties of chalcedony that were black and brown were referred to as onyx, but today the term is usually used only to refer to the black stone. Onyx which is reddish brown with white bands is referred to as sardonyx. The primary onyx deposits are found in India, Brazil, California, and Uruguay.

Other important varieties of chalcedony are chrysoprase, carnelian and jasper.

Alexandrite

Alexandrite is a variety of chrysoberyl and is the third hardest naturally occurring gemstone in the world. It was discovered near the Tokovaya River in the Ural Mountains in April 1834, and is named after the Czar Alexander II of Russia.

Chrysoberyl is a durable gem with a hardness of 8.5 on the Mohs scale. While most chrysoberyl is yellow, brown or green, alexandrite is a rare variety of the mineral, whose most alluring quality is that it exhibits different colour when exposed to natural light and artificial light. This shift of colour does not indicate that the stone itself changes colour in different light, but merely that it reflects the change in the light in its surroundings. Alexandrite is green or bluish-green in daylight and turns red under artificial light.

Alexandrite also differs from other chrysoberyls in its mineral composition. Not only does it contain titanium and iron, but it also contains chromium as a major impurity that accounts for the change in colour of the stone. Alexandrite is also very scarce because of its chemical composition. The primary source of alexandrite had been the Ural Mountains for almost a century before it was discovered in Hematita in Minas Gerais, Brazil. Today, alexandrite is also found in Sri Lanka, Myanmar, Madagascar, India, Tanzania and Zimbabwe.

Alexandrite is most commonly found in period jewellery because of its scarcity. Most of the alexandrite produced today is from India, but this too is not a substantial amount. The stone was discovered in the Karaka Hill region of the Raipur district in Chattisgarh in 1994, but the amount of alexandrite being produced from this deposit has been steadily declining over the years. The majority of Indian alexandrite produced today comes from Andhra Pradesh.

Amethyst

The amethyst has had legends and lore associated with it for centuries. The word amethyst comes from a translation of the Greek word 'amethystos', meaning 'not drunken'. Amethysts are thus believed to protect the wearer against intoxication, as well as to protect against evil spirits and stir arouse intellect.

A variety of the mineral quartz, the amethyst is a purple stone that gained favour with royalty worldwide. The stone is included in the British crown jewels, and was also patronised by Catherine the Great of Russia and several Egyptian queens. Since the Middle Ages, bishops' rings have also been made of amethyst, and it is thus referred to as the stone of the bishops. The purple colour of the gemstone is attained by the presence of iron in the quartz, but can be changed with heat treatment. Heating an amethyst can alter its colour to yellow, red, or even colourless. Green amethysts are becoming increasingly popular and can only be created by heating.

The best quality amethysts are transparent gems, clean and free of inclusions. To highlight the beauty of its purple hue and clear texture, the finest amethysts are usually cut as brilliant rounds to maximise the colour and lustre.

Amethysts are also durable gems, with a hardness of 7 on the Mohs scale. They are thus appropriate for daily wear, although they must not be exposed to prolonged and intense heat in order to prevent discolouration.

Brazil is the largest producer of amethysts today, followed by Uruguay and Madagascar. Other countries where amethysts can be found in smaller quantities are Bolivia, Zambia, Namibia, Russia and Myanmar.

Peridot

Peridot or the ‘golden stone’, originally known as topazion, is a variety of the mineral olivine and is transparent and bright yellow-green in colour. The earliest reference to the gem is in the Historia Naturalis written by the Roman historian Pliny in the 1st century. Pliny gives a detailed account of a gem named ‘topazion’ and dates its discovery to approximately 300 BCE. He writes: “Juba says that there is an island in the Red Sea called ‘Topazion,’ at a distance of three hundred stadia from the main land; that it is surrounded by fogs, and is often sought by navigators in consequence; and that, owing to this, it received its present name, the word ‘Topazion’ meaning ‘to seek’.”

Pliny’s island of ‘Topazion’ later known as Zabargad, was the largest of a group of islands off the south-eastern coast of Egypt in the Red Sea. Zabargad was once an oceanic volcano, which became visible above sea level after Africa and Asia's tectonic plates collided. As a result of its unique mineral forming conditions, the Island of Zabargad once possessed large deposits of the gem forsterite-olivine or Peridot. The ancient Egyptians treasured this beautiful green-gold gem and some of Cleopatra’s famed emeralds are now believed to have actually been peridots.

The origin of the word Peridot itself is unclear. In fact, fascinated by its radiant green colour, the Romans nicknamed it ‘the evening emerald’. The gem assumed the name peridot sometime in the 13th century, a term perhaps derived from the Arabic word faridat meaning ‘gem’ or the French word ‘peritot’ meaning ‘unclear’. From the 18th century onwards, the name peridot alone was used.

Considered to be a sacred gem, the peridot was a symbol of purity and virtue. The stone was believed to have magical properties and was worn as protection against evil. Peridot is said to protect the body’s aura and bring its wearer success, peace and good luck.

Other ancient sources of the stone include Burma, South Africa and Brazil. In recent times, the United States, Pakistan and Kashmir are the largest producers of peridot. A gem associated with success, power and good luck, peridots feature in the collection of the Nizam of Hyderabad. Mahboob Ali Pasha, the sixth Nizam was particularly fond of the gem and had them set into belt buckles, rings and coat buttons.

Tanzanite

The geographical origin of the Tanzanite can be easily garnered from the name of the gem – the East African nation of Tanzania is the only place on Earth where this beautiful blue stone is found.

How Tanzanite was created and discovered, on the other hand, is anything but simple. It is estimated that the creation of the stone began over 500 million years ago with the eruption of the volcano we now know as Mt. Kilimanjaro, which caused a shift in the physical and chemical properties of the earth around it, allowing the Zoisite crystals there to develop into Tanzanite.

Tanzanite was discovered only as recently as 1967 by Masai tribesmen tending to their cattle in the Merlani Hills of Tanzania. According to legend, heat from a grassfire near Kilimanjaro turned the naturally brown zoisite crystals into a fantastic shade of blue, and the Masai tribesmen, enthralled by the sea of blue stones they had never laid eyes on before, became the first human gatherers of Tanzanite. Even today, the areas where significant deposits of Tanzanite can be found and commercially mined comprise a mere four square kilometers near the towns of Arusha and Moshi in the Merlani Hills.

Zoisite is naturally found in a variety of colours ranging from brown to green. Treating the mineral with heat can impart it with a brilliant blue colour, and it is blue zoisite alone which is known as Tanzanite. Some Tanzanite may include a purplish tinge, and is the most coveted variety of the stone, as the purple and the blue complement each other magnificently.

Tanzanite is one of the few gemstones that can only be found in a concentrated region of the world, and this unique factor makes it highly sought after. The ever changing political, social and economic conditions of Tanzania also ensure that the stone is coveted, since collectors and suppliers cannot turn to another source to acquire it.

Tanzanite is believed to have calming and balancing properties and was added to the American Gem Trade Association’s list of birthstones, as the birthstone for the month of December.