OTHER TYPES OF GEMSTONES
We have covered most of the gemstones especially the precious ones within this website. There are other stones that may be of interest
In the red spectrum…
A pinkish orange stone from the parent spodumene. Found in 1902 in California and sent to Tiffany’s mineralogist George Kunz. He thought it to be spodumene but not seen before in this colour. It was named in Kunz’s honour in 1903 and is now a highly prized gem. Another stone in the same group is the green gem material called Hiddenite, discovered in California in 1879. For more information on this group of gems visit the website www.pelagems.com
Often thought to be an imitation gemstone this gem comes in many colours but in red it looks particularly good and a substitute for ruby in many cases, but of course at a fraction of the price. The red colour is caused by chromium , sometimes called rubicelle. If iron is present then the colour is blue., It can be cut as a facetted stone, and sometimes as a cabouchon, this is a smooth pebble like cut, also know as a carbuncle. Found it granites and metamorphic rocks it is often found in the waterworn pebbles in the gem gravels of Burma, Sri Lanka and Madagascar.
However the stone has been simulated since 1910, and has been used to imitate many precious gemstones, and the name derives from the Latin, spina meaning little thorn, this refers to the sharp points on some crystals.
In the yellow/orange/brown spectrum
A stone long used in the production of jewellery and also known as brown quartz. It comes from the Cairngorm mountains of Scotland, where it is also called a Cairngorm. When irradiated the colourless quartz changes colour to grey brown, suggesting that natural brown quartz may have been formed by natural radiation. Brazil is another source of the stone and crystals weighing over 300kg have been found. Most stones for jewellery use have been heat treated to obtain the deep chocolate colouration which is quite normal. Smoky quartz has been fashioned not only for jewellery, but polished to form majestic scent bottles and intaglio seals, especially popular with the ancient Romans
This is also known as a grossular garnet which does appear in a whole range of colours, but the popular orange brown colour is formed when manganese and iron are present, the green colour mined in Kenya, Canada, Pakistan among others has also been called Tsavorite. In Madagascar it is often referred to as the cinnamon stone. Both the ancient Greeks and Romans made cameos and cabochon stones from hessonite as well as for jewellery. It can be worn as the birthstone for January, like garnet.
Also referred to as Chalcedony this opaque stone has long been used in the production of men’s signet rings. Once thought to still the blood and calm the temper! Its colour density depends on the presence of iron oxides. The best variety is found in India where it is placed in the sun to change brown tints to red. It should not be confused with jasper which is usually translucent, cornelian is always opaque.
This stone occurs in a range of different colours, the familiar sherry orange brown to pink, blue and green. Natural pink topaz are rare so most are actually heat treated to bring the colour to pink, a practice that is legal and understood and to be able to sell at a reasonable price. The blue variety are also irradiated are are similar in colour to aquamarine.. Topaz is found in igneous rocks such as pegmatites, granites and volcanic lavas. The main sources are in Brazil, the USA, Sri Lanka and a number of other countries. Brazil and Pakistan are known for the natural pink topaz, and this variety in mythology has been worn around the neck to dispel bad omens, calm anger and heal poor vision.
The name is said to have come from the Greek name for a small island in the Red Sea called Topazious , now called Zabargad, although some scholars trace the origin of the name to India, the Sanskrit word for fire, being tapaz. Today the stone is the birthstone for November , and has been used for various wedding anniversaries, the 4th, 19th, or the 23rd. Russia named one variety the Imperial Topaz, and was worn by Czarinas in the 18th and 19th centuries. The most famous was the 1680 carat stone, which was colourless and known as the ‘Braganza Diamond’, and set into the Portuguese crown jewels.
The green spectrum
Also called olivine the pale green olive like colour is due to the presence of the presence of iron and has a distinctive oily lustre. Found in Egypt, China and Brazil among others the stone was brought to Europe in the Middle Ages by the Crusaders where peridot had been mined for over 3500 years.
It is the birthstone for August, and for the 16th year of marriage. In the 19th century the mines on St Johns Island in Egypt produced millions of dollars worth of the stone, but by the 193os this had tapered out, and by 1958 it was no longer found in that region.
A stripy green stone which is opaque and cannot be facetted. It was thought that it would ward off danger and illness, and success in business. It is found mostly in Zaire and Russia. The name derives from middle French melochite meaning mallow green and its resemblance in colour to the mallow plant.
Thought for many centuries to be a single gemstone but in 1863 it was recognised as not so, one being jadeite made up of interlocking granular pyroxene crystals which occurs in a wide range of colours from just the usual green to white, orange, red, blue and black. The other is nephrite jade and is found in fibrous amphibole crystals. These form an interlocking structure tougher than steel and excellent for carvings and again colours vary from moss green to cream colour magnesium rich material.
Jadeite’s rich green colour called imperial jade is due to chromium. It moistly is found in Burma which has supplied China for over 200 years, and Guatemala was another important source.
Its history goes back thousands of years and was used by Stone Age people to shape into weapons, tools and ornaments. In China it has been used and treasured for over 3000 years, and it was known as ‘ju’ or the Royal Stone. It was so precious that there were wars in China over some of the largest precious jade stones. Today rare and antique ornaments fetch huge prices at auction, as the Chinese proverb goes, ‘ gold has a price, jade is priceless’. Early Spanish explorers used it to cure aches and pains, especially in the hip and leg after they saw natives holding pieces of the stone to their sides to alleviate pain.
Not known to many and only used occasionally in jewellery . Usually bottle green to brown in colour, and its the increase in iron in the material that makes the colour a deeper green. The very bright green in the stone is due to an excess in chromium. Said to promote emotional well being.
In the blue/violet spectrum
known as lapis lazuli a blue rock made up of several different minerals, including sodalite, hauyne, calcite and pyrite. It is the little gold specks in lapis that are in fact the presence of pyrites. Found in limestone boulders and used often in jewellery and ornaments in Afghanistan , and has been used in Egypt and was found in the mask of Tutankhamen. Argentina also has a rich source. It was believed that a wearer of lapis would be protected from evil.
The region if Afghanistan called Bactria has been excavating the stone since 700BC, and still extracting the mineral today, and seen as one of the world’s oldest known commercial gemstone. Traders took the stone to all parts of the Middle East and India where it was cut into beads and cabochons, and it has been cut into bowls, dagger handles, hair combs and amulets.
A violet blue gemstone also known as cordierite has also been called a water sapphire due to its similarity to that stone when cut. It is found in many countries, especially Sri Lanka, Burma and Madagascar. The name derives from the Greek word ios which means violet. The Vikings used the stone’s pleochroism a virtue by using thin slices of the stone as a light polariser to navigate their trips. By observing the sky through these they could locate the exact position of the sun on overcast days, cancelling out the haze.
Used for a 21st wedding anniversary and as a substitute for September birthstone
Most famous for its colourless stone this should not be confused with cubic zirconia which is a man made simulate for diamond. Zircon does however closely resemble a diamond. Blue zircon has been used extensively over the years and this colour is obtained when the stone is heated. These come from Vietnam and Thailand and have been used in jewellery particularly in the early to middle part of the 20th century. The clear stones can be identified from diamonds if closely viewed as they often have small surface marks or chipped edges being a softer material than diamond.
The wearer of zircons was often thought to be blessed with wisdom, honour and riches, and any loss of lustre was thought to worn of danger ahead. The name derives from the arabic zargun which means gold colour. They do come in a variety of colours and the golden brown ‘gold’ colour is the most sought after for jewellery.
This ever popular opaque stone has been mined for over 2000 years. Persia was a known mining area for the stone and are known for their robin’s egg blue colour. They believed the stone represented heaven due to its sky blue colour . Native American tribes worshipped the stone and the Aztecs believed the stone was sacred and made intricate masks and other adornments for special ceremonies.
The colour in the stone is due to copper aluminium phosphate, it is the copper that gives it a blue to green colour. Sometimes if zinc is present it has more of a yellowish tinge. It is formed when a chemical reaction in the veins of rock, the copper and aluminium , forms clumps of turquoise material. The matrix effect is seen in this stone, this being brown lines that run through its form and when seen in its raw state.
Turquoise has been thought to warn the wearer of danger or illness by changing colour, and has often been imitated. It is possible to powder the stone and mix with epoxy resin and glue to form a stone that can then be polished. Good plastic can also be used. However the only way to really test this is by heating a needle. If the hot end penetrates the stone and gives off an acrid smell you will know it is plastic, the real thing will not allow penetration of its surface. This works well on amber too.
A stone that in recent years has become very popular with the public. Tanzanite is found in only one place on Earth, that being Merelani in Tanzania. The stone was initially discovered by a Masai tribesmen in 1967 and he showed it to a local fortune hunter called Manuel d’Souza who quickly registered his mining claims. In belief that it was a new sapphire deposit he did not realise that he had in fact laid claim to one of the world’s rarest ever gems. It was Tiffany & Co that recognised the potential of this gem and did a deal to become its main distributor. Almost overnight it became one of the world’s most sought after gemstones.
It is in fact a specific colour of zoisite, and what makes it special is the rare effect it shows by giving a balance between blue and purple when viewed from different directions.
Tanzanites are often heat treated to bring out the density of colour, quite normal in the gem supply world, as sometimes there is some brown colour in the natural stone. In fact most of the natural stone when extracted from the mine is more brown in colour and heat treatment is the only way to get the natural purple colour out of it. It is odd that this stone lay dormant and undiscovered for so long, and one story is that a bushfire may have accidentally heated the natural brown zoisite and created the beautiful purple now known as tanzanite.
It has been designated as the official birthstone for December, although turquoise shares this too, and for the 24th year of marriage. It has a similar hardness to emerald, and it has quite a high refractive index and with its birefringence compared to other blue stones has quite a distinctive brilliance and sparkle. The largest crystal ever found was over 16,000carats large, and called the Mawenzi after the second highest peak of Kilimanjaro.
What is termed as ‘precious coral’ is taken from deep water rocky seabeds with low levels of sedimentation. It is slowly built by small marine animals known as coral polyps, these being found in dark caverns and crevices., Bit by bit over a long period of time the shells build up to form complex branches and skeletal structures composed of hardened calcium carbonate and coloured by cartooned pigments.
Most coral used in jewellery are varieties of corallium rubrum or noble coral, one of the most popular corals are known as the ‘angel skin coral’ a pink to salmon coloured coral.
The protection of coral is a very current issue as many coral fields are being destroyed, but mostly by types of dragnet fishing rather than collection for jewellery use. Some areas are however protected, Hawaii is one example. However China is regulated by permits. Italy has been one major trading nation of coral and some others areas of the western mediterranean, also the Midway Islands, Japan and Australia.
The stone has been popular from the 1st century AD and used by the Gauls in their helmets and weapons as they believed it was a protective stone. The Romans hung branch coral around the necks of their children to protect them from danger. It is not a particular stone for any birth month, but mythology has suggested that the wearer is protected from danger if their birthdays fall under the Zodiac signs of Pisces, Scorpio or Capricorn. It is the stone used for the 35th wedding anniversary.
It is a good idea when cleaning coral, or any organic gemstone to use a soft cloth rather than cleaning fluids, and do not leave in direct sunlight as this will fade the colour. Also as with pearls, when using perfumes or hair spray always put this type of jewellery onto yourself after such applications, and when storing wrap in acid free tissue.
A very contentious issue this, and we as a company will not stock or purchase ivory from any source whether protected or not. If we do purchase any antique ivory we will sell at auction and the money we donate to the WWF for the protection of elephants. It is an issue that the owners of Charles Hart and Vintage Tom very seriously.
However, we cannot ignore the fact that for centuries ivory has been traded from many countries to produce beautiful and intricate designs in ornamentation and jewellery making, it’s just we feel it looks better on the animal in the raw state. For many years ivory was taken only from elephant tusks, but today in fairness this has been outlawed and ivory if it is used at all comes from fossilised sources along with narwhal, seal lion and wild boars teeth.
To distinguish ivory from bone there is a distinctive graining which is referred to as the ‘engine turned effect’, and as ivory ages it turns from white to yellow cream and then to a brown patina. However throughout ancient and modern history ivory has been treasured and simple amulets have been found dating back 7000 years,and the Chinese penchant goes back to 5000BC!
The majority of the older carvings come from Asian elephants found on the male animal, but in recent times the African elephant has been hunted for the material. It was staggering just how many items were made from ivory before the invention of plastics. Buttons, piano keys, billiard balls and furniture inlay to name but a few.
By the 1970s environmental movements managed to gain some influence and by 1989 a worldwide ban has been implemented. The downside to this of course is that being illegal to kill elephants for ivory has meant that those who do so illegally have a product to sell that is infinitely more valuable, and antique ivory items are going to be that much more expensive due to there being less available.
There have always been simulants for ivory, both bone and vegetable ivory (from the doum palm or tagua nuts) have been used, and from the late 19th century celluloid and casein were widely used and today modern plastics look very good with the ‘grain’ added to give the authentic ivory effect- so much better than the real thing- in our opinion! Ivory was used for the 14th wedding anniversary, but today we suggest that pearl would be a good alternative.
For those who own ivory and would like to sell to us, we can arrange to send to auction for you and then present a cheque to a charity of your choice.
SOME USEFUL TERMS USED IN GEMMOLOGY-
Asterism- the star effect seen on some stones like sapphires
Cabouchon- a gem cut to form a dome, sometimes called en cabochon
Chatoyancy- The cats eye effect sometimes seen on some stones
Cleavage- the breaking of a stone along its natural weak fault line
Crown- the top part of a stone, especially a diamond
Dichroic- refers to a stone that appears to have two different colours, as in water melon topaz
Diffraction- the splitting of white light into its spectral colours
Dispersion- also known as fire, again the splitting of white light into its spectral colours
Doublet- a composite stone made of two parts and glued together
Facet- surface cut of a polished gem
Heat Treatment- when a stone is treated in a laboratory to enhance or change its colour
Inclusions- small marks in a stone, sometimes useful to identify a stone
Paste- a glass substance made to imitate a gemstone
Pavilion- lower part of a stone under the middle portion called the girdle
Refraction- the bending of light as it passes from air into a different medium
Rough- a term used to describe gem material or crystals still in the rock
Specific Gravity- density as measured when it is compared to an equal volume of water
Step cut- a cut characterised by a rectangular table facet and girdle
We have a huge selection of gemstones available in our online store at Vintage Tom, so please browse our store and get in touch if you have any questions.