ABSTRACT
O’Donoghue, M. (1987) Quartz, Butterworth-Heinemann, Oxford O’Donoghue, M. (1988) Gemstones, Chapman and Hall, London O’Donoghue, M. (1997) Synthetic, Imitation & Treated Gemstones, ButterworthHeinemann, Oxford Pagel-Theisen, V. (1980) Diamond Grading ABC, 7th edn, Pagel-Theisen, Frankfurt Read, P.G. (1983) Gemmological Instruments, 2nd edn, Butterworth-Heinemann, Oxford Read, P.G. (1988) Dictionary of Gemmology, 2nd edn, Butterworth-Heinemann, Oxford Rouse, J.D. (1986) Garnet, Butterworth-Heinemann, Oxford Schumann, W. (1977) Gemstones of the World, NAG, London Sinkankas, J. (1985) Gem Cutting, 3rd edn, Van Nostrand, New York Sinkankas, J. and Read, P.G. (1986) Beryl, Butterworth-Heinemann, Oxford Smith, G.F.H. (1972) Gemstones, 14th edn, Chapman and Hall, London Themelis, T. (1992) The Heat Treatment of Ruby and Sapphire, Gemlab Inc., USA Theophrastus (1774) History of Stones, London Tolanski, S. (1962) The History and Use of Diamond, Methuen, London Walton, Sir J. (1952) Physical Gemmology, Pitman, London Watermeyer, B. (1980) Diamond Cutting, Purnell, Cape Town Webster, R. (1976) Practical Gemmology, 6th edn, NAG, London Webster, R. (1979) The Gemmologist’s Compendium, 6th edn, NAG, London Webster, R. (1994) Gems, 5th edn, Butterworth-Heinemann, Oxford Yaverbaum, L.H. (1990) Synthetic Gems – production techniques, Noyes Data Corporation, Park Ridge, NJ
Chemical composition, varieties, constants, characteristics and occurrence
Amber Composition: Fossilized tree resin containing a mixture of hydrocarbons plus some succinic
acid, and consisting mainly of carbon (79%), hydrogen (10%) and oxygen (11%) Varieties: Opaque white, lemon, golden, red-brown, brown and black. Translucent to
transparent colourless, pale yellow, deep yellow, light to deep red, and occasionally green and blue/grey
Refractive index: 1.54 Specific gravity: 1.05-1.10 Hardness: 2.5 Lustre: Resinous Luminescence: Bluish white (LW UV), greenish (SW UV) Inclusions: Plant particles and insects, bubbles Occurrence: Sea amber from the Baltic and North Sea coasts. Pit amber from Sicily,
Romania, Myanmar, the Dominican Republic and Kaliningrad in the former USSR
Copal Composition: A younger fossil tree resin than amber (sometimes used as an amber simulant) Constants: Copal resin has constants similar to those of amber, but unlike amber it is
softened by ether, has a crazed surface, and crumbles easily under the knife blade Inclusions: Occasionally contains insects Occurrence: East Africa and South America
Coral Composition: A branching tree-like structure formed by the skeleton remains of various
types of marine polyp, and consisting either of a fibrous aragonite form of CaCO3 (white and pink varieties) or of a horn-like material of conchiolin (black and golden varieties, although these are not strictly corals in the gemmological sense)
Varieties: White, pink (‘angel’s skin’), red, golden and black Refractive index: About 1.48 for carbonate coral; 1.56 for conchiolin type Specific gravity: 2.60-2.70 for carbonate coral; 1.37 for the conchiolin type Hardness: 3.5 for carbonate coral; 2.5-3.0 for the conchiolin type Lustre: Waxy Occurrence: White, pink and red coral is found in shallow subtropical waters in the
western Mediterranean and the Malay and Japanese seas. Black and golden coral is harvested off the Malaysian Archipelago, the coastline of northern Australia, in the Red Sea and off the Hawaiian islands
Ivory Composition: Ivory consists almost entirely of dentine, although enamel and other
organic substances are associated with the complete tusk or tooth Varieties: Ivory is obtained from elephant tusks, the tusks of the walrus and the
hippopotamus, the teeth of the narwhal and the sperm whale and, more rarely, the tusks of fossilized mammoths
Refractive index: A vague refractometer reading about 1.54 Specific gravity: 1.7-2.0 Hardness: 2.0-3.0
Jet Composition: Organic, carboniferous with traces of mineral elements. Jet is a form of
fossilized wood (similar to lignite or brown coal) halfway in formation between peat and bituminous coal
Varieties: Hard jet and soft jet (black and dark brown) Refractive index: 1.64-1.68 Specific gravity: 1.3-1.4 Hardness: 2.5-4.0 Lustre: Resinous Fracture: Conchoidal Occurrence: France, Germany, Spain, UK (on the Yorkshire coast around Whitby),
USA and the former USSR
Odontalite Composition: A bluish fossil bone or ivory obtained from prehistoric animals such as the
mammoth. The bone contains calcite and owes its colour to vivanite, an iron phosphate. It is also known as bone or fossil turquoise, and is used as a turquoise simulant
Refractive index: 1.57-1.63 Specific gravity: 3.0-3.25 Hardness: 5.0 Occurrence: France
Pearl (native) Composition: Calcium carbonate (86%), conchiolin (12%), water (2%) Varieties: White, black and pink blister, cyst and fresh-water pearls; non-nacreous
pink conch pearls Refractive index: 1.52-1.66 (1.53-1.69 for black pearls)
