Gemstone Review – Jewellery: Popular Gemstones – Agate to Emerald – agate gemstone properties
agate gemstone properties –
AGATE – Agate consists of silicon dioxide which was sedimented in ancient times to form beautiful flowing bands of different texture and colours. There are always many layers and bands of differing materials in all sorts of designs and colours – in quartz, chalcedony, jasper, or iron oxides – making agate one of the most intriguing gemstones for lapidary. Agates of all kinds have been popular in talismans over the centuries. Beautiful specimens of concentric rings are found at Winona, Minnesota. Heating agate artificially produces even more spectacular agates. There are many different kinds of Agates: Moss Agates or Seaweed Agates, Agatized Coral, Crazy-lace Agate, Plume Agate or Scenic Agate, Tree Agates, Onyx Agate, Eye Agate and Rainbow or Iris Agate with its many colours.
AMBER – The name is Arabic but it has come to us from the French and in Greek it means ‘electricity’. Pliny asserted amber as the sap of certain trees. It is now confirmed to be the fossil resin of an extinct species of pine tree of the Tertiary period. . It frequently preserves within itself plant structures and insects. In prehistoric it was used as a talismanic charm against disease and also burnt as incense. It has a peculiar electrical property discovered by Thales, one of the 7 sages of Greece, when it is subjected to friction on a natural woollen material to demonstrate an electro/magnetic power. Amber is found in colours from green to gold and orange, brown and even red. It is found either clear or opaque in nature with any cloudy appearance caused by imprisoned bubbles. Amber was also employed as an essence or scent and still is used as an ingredient in modern perfumes. Amber has wide distribution in Europe, Sicily and the Adriatic, Australasia, America and Russia, Siberia, Greenland, U.S, Mexico, Burma and Romania . It is occasionally washed up on beaches.
AMETHYST – Occidental or True Amethyst is a form of quartz. or coloured Rock crystal consisting of silica. Oriental amethyst is alumina. Others are violone, a silicate of aluminium and lithium. It contains iron in the quartz. The deeper the colour, the more valuable – due to presence of manganese oxide. Oriental Amethyst or Violet Sapphire is a form of corundum and similar to sapphire and ruby. A beautiful sample is a violet gem weighing 48 carats in the Allison Gem Collection, Australia The best examples come from Siberia, Ceylon, Brazil and Persia but a large one found in a cave of amethyst in Brazil is a huge crystal which measures 33′ by 6′ x 3′- the largest ever found.
AQUAMARINE – This gemstone is a transparent, pale water blue beryl with iron giving it the green/blue tint, varying from pale green to deep sea green. It is relatively inexpensive and mined in India, Siberia and Brazil, the most abundant source of aquamarine. This blue green stone is heated to produce the blue colour so popular in modern jewellery. A magnificent example of 46 carats is in the Allison Australian gem Collection.
BERYL – Beryl is used as a copper alloy and also in constructing the atomic bomb. Beryl and Aquamarine differ only in colour – Beryl is bright blue to white and Aquamarine is sea green to deep green. Best known is the deep green form of beryl, the precious emerald. The yellow beryl is the heliodor and pink beryl is morganite and there is also an extremely rare Red Beryl. Beryl is known for its huge crystals. Madagascar yielded a single crystal weighing nearly 40 tons far surpassing the 18-27 foot monster ones previously obtained from New England.
BLOODSTONE – Bloodstone is opaque and always cut as a cabochon, or un-faceted stone. It is a variety of green Jasper with many blood red specks in its composition. These are formed by iron oxide with which it is impregnated. Ancient Egyptians highly valued bloodstone amulets. It was once very popular in cutting seals and cameos. Found in India, Siberia and Russia. The Chinese believe it produces best results when set in gold.
CARNELIAN (Cornelian) – This is a translucent, orangey-red chalcedony sometimes found in yellowish tones and white, frequently with two combined. On exposure to the Sun the hues become brighter but not in artificial light. It is capable of high polish which was why it was considered as the best stone to use as a seal, according to Pliny. The transparent red type of carnelian is known as Sard and comes from Arabia, India, New Zealand, Europe, Mesopotamia, Surinam and Siberia. Many ancient Etruscan and Egyptian scarabaei have been found carved from this stone. Buddhism includes this in sacred 7 stones -Tibetans call it A-yu and as talisman has occult properties.
CORAL – Coral is formed by calcium carbonate in the skeletons of colonies of soft bodied molluscs in tropical waters. It ranges in colour from the rare black, to pink and reddish-orange, the classical “coral” of fashion. It is also found in a blue colour. The ancient Romans and Greeks used it in ornamentation. Red, pink, white and blue corals are made of calcium carbonate but black and golden corals are formed of the horny substance conchiolin. In all corals the skeletal structure is visible as delicately striped of spotted graining. Red and pink corals from the Mediterranean. were popular for centuries and often used in rosaries. There was an extensive trade through Europe into Arabia and to India where coral was also used medicinally. The black and golden corals fished off Hawaii, Australia and West Indies are more recent discoveries.
CRYSTAL – Rock Crystal or Frozen Water has always been considered a pure stone and once used as a divining stone and in modern fortune telling when the gypsies keep the tradition alive in using a crystal ball, a custom which is said to have begun in Persia. The stone is traditionally associated with mystical properties and linked to the moon. It is one of the 7 sacred substances of Buddhism. Its crystal has 6 sides and rarely is it found in large pieces – but the largest quartz crystal ever found was in Brazil – it was over 5m long and weighed more than 48 tonnes! Synthetic rock crystal is manufactured in Japan for industry and also jewellery.
DIAMOND – Diamond – the beautiful and most popular precious stone consists of pure carbon, the blackest of substances, which crystallizes in the cubic system at enormous pressures and high temperatures, sometimes from depth of 150 km in the earth. Apart from its unique flashes of light and colour from its faceted stone, the diamond has special properties and is the hardest of all stones. The best gem quality stones are colourless and transparent with a slightly blue tint but the pink and tinted diamonds are becoming popular also. Diamonds are said to have first been found in India more than 2000 years ago. Previously in that country diamonds were known but were never cut because it was believed that it had magical properties were destroyed by cutting. Cutting in Europe began after 1300 AD. Lasers are now used to cut diamonds but the only mineral capable of cutting a diamond is a diamond. Top world producers now are northern Australia which supplies 1/4 of the world’s needs – particularly for industrial purposes and also the coloured “champagne diamonds” and in the South African Kimberley region.
EMERALD – Emeralds are green forms of Beryl and the best are found in Bolivia, Brazil and Colombia. Also India and Pakistan but the finest are said to come from Colombia near Chivor where they occur in veins within dark shales and limestone. The Ural Mountains which are rich in emeralds retain the world market. Egypt’s emerald mines are over 4,000 years old. Pliny speaks of a colossal emerald statue of Serapis 13 1/2 feet high, in the ancient Egyptian labyrinth. It was called the “king” of green stones with extremely high value because of its rarity and the fact that seldom was there gemstone cut that was without flaw. The largest known emerald discovered was 11,000 carats found in an uncut state in South Africa. The largest cut stone of quality was 1,347 carats but it had obvious flaws. The largest perfect stone known was the Tsar of Russia’s – 30 carats. The Crown of the Andes made in 1593-99 in South America had 453 emeralds the largest being of 45 carats. However synthetic emeralds in modern times have plausible inclusions so testing must be done carefully in determining the quality of stone.
– Jewellery: Popular Gemstones – Agate to Emerald
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