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- Ear-shells see Abalone.
- Egeran a name applied to the variety of idocrase found at Eger, Hungary. See Idocrase.
- "Egyptian alabaster" name applied to a banded calcite. The alabaster of the ancients being calcite. The modern alabaster is massive gypsum.
- Egyptian jasper jasper in which the colours run in zones.
- Egyptian marble a marble stained black by bitumen and veined yellow with dolomite. It is usually obtained from Italy.
- Eight-cut a simple modification of the brilliant-cut used for small diamonds. The table being surrounded by eight foursided faces. See Cuts of stone, see Chart 186.
- Eilat stone a blue to green mottled stone consisting of a mixture of chrysocolla and other copper minerals. Found in Israel.
- Ekamte a metamict calcium thorium silicate; R.I. 1-60; S.G. 3-28; H. 6.5. Stones have a green colour, are singly refractive and are radio-active. Only known source is Ceylon.
- Elaeolite a massive variety of the mineral nepheline R.I. 1-538 --- 1-542; H. 5 to 6; S.G. 2-55 to 2-65; Hexagonal; Colours, green, red, brown, blue and grey.
- Elath stone same as Eilat stone, which see.
- Electron volt Unit of energy used in nuclear physics. It is used by physicists rather than wavelength to which it has a definite relation.
- Ele Emery an intimate mixture of granular corundum, magnetite and some haematite. Often used for abrasive purposes, the grain is found to break down under pressure, so that new cutting edges are constantly present. The material is best suited for polishing purposes.
ctro-conductivity; when a substance, whether mineral or not, after being held between two electrodes at different electrical potentials allows current to pass the substance is said to be electro-conductive. The test has a value with blue diamonds, for, as far as has been found, all natural blue diamonds conduct electricity as they are of the Type IIb, while the diamonds artificially coloured by electron bombardment are not electro-conducting.
- Electro-magnetic spectrum the term used for the range of wave-lengths of radiant energy from the long waves of wireless to the extremely short wave-lengths of the cosmic radiations. Below the wireless waves come the infra-red or heat rays, light rays, ultra-violet rays, X-rays, the gamma rays of radium and the cosmic rays.
- Electroned diamonds diamonds coloured an aquamarine blue colour by treatment with high-speed electrons from a Van de Graaf generator. The colouring is only skin deep and the stones are not radio-active, nor are they electro-conductive.
- Emerald grass-green beryl, which see.
- "Emerald, African" green fluorspar.
- "Emerald, Brazilian" a MISNOMER ( COMMERCIAL LABEL ) for green tourmaline.
- Emerald coated beryl cut and polished aquamarine or yellow beryl upon which a coating of synthetic emerald has been deposited. See Emerita.
- "Emerald, Evening" a MISNOMER ( COMMERCIAL LABEL ) for peridot.
- "Emerald matrix" a MISNOMER ( COMMERCIAL LABEL ) for green fluorspar.
- "Emerald, Oriental" a MISNOMER ( COMMERCIAL LABEL ) for green corundum.
- "Emerald, Scientific" may be synthetic corundum or spinel, a beryl glass or just paste.
- Emerald, Spanish" a MISNOMER ( COMMERCIAL LABEL ) for green glass.
- Emerald, Synthetic see Manufactured stones, Chart 171.
- "Emerald, Synthetic" a MISNOMER ( COMMERCIAL LABEL ) for the green variety of synthetic corundum or spinel.
- "Emerald, Uralian" a MISNOMER ( COMMERCIAL LABEL ) for demantoid garnet.
- Emerald-cut name applied to a diamond cut in the trap (step) cut style, so called from the method of cutting emeralds. See Cuts of stones, Charts 181, 185.
- "Emeraldine" a MISNOMER ( COMMERCIAL LABEL ) for a chalcedony stained green with chromic oxide. It is a deeper green than the stained chalcedony which owes its colour to nickel and, unlike the nickel type, shows a red residual colour under the dichromatic filter
- "Emeraldite" a MISNOMER ( COMMERCIAL LABEL ) for green tourmaline.
- "Emerita" the name given to the emerald coated beryls made by the Lechleitner process which causes a deposit of synthetic emerald on to the surfaces of previously fashioned aquamarine or yellow beryl. Now called "symerald".
- Enantiomorphism crystals which show right and left-handed formation, not only in their outward appearance but in their optical properties also are said to exhibit enantiomorphism. These crystals show circular polarisation. Example, quartz.
- Endoscope an instrument for the detection of cultured pearls. It depends upon the difference between the concentric structure of real pearls and the parallel structure of the motherof-pearl bead in cultured pearl. Can only be used for drilled pearls.
- Enstatite R.I. 1-665 --- 1-674; S.G. 3-25 to 3-30; H. 5.5; Rhombic; Colour, green; Localities, South Africa. Burma.
- Eosite an aventurine quartz with reddish veins. The best of this material is probably from the Altai Mountains of Russia.
- Epiasterism a star effect seen in a suitably cut cabochon stone when light is reflected from suitably oriented inclusions within the stone. The asterism of star corundum is of this type.
- Epidote R.I. 1-735-1-765 ; S.G. 3-25 to 3-50; H. 6 to 7; Monoclinic; Colours, yellow, green, pistachio green, brown, and red; Localities, Italy, France, Germany and Alaska. Alternative name "Pistacite".
- Epithelium the name applied to the surface layer of cells of the "mantle" which covers the pearl oyster. These cells have secretory powers and produce the pearl-shell and the pearl.
- "Erinide" an American trade-marked name for greenish synthetic spinel.
- "Erinoid" a trade name for the formalised casein plastic.
- Essence d 'orient a preparation of fish scales (from the underpart of the "bleak") which is used to produce the orient in imitation pearls.
- Essonite see Garnet, Hesso''ite.
- Etch figures small geometrical elevations or depressions produced on the faces of crystals due to solvent action, and which have a ciefinite relation to the internal crystal structure.
- Ether (ethyl ether) a volatile inflammable liquid used as a test for amber and copal. Copal is softened by this liquid while amber is unaffected.
- Ethylene dibromide a useful liquid with a low surface tension which thus may be used in place of water or density determinations by the direct weighing method. It is necessary to correct for temperature when using this liquid. See Correction Tables Chart 229.
- Euclase R.I. 1-650 --- 1-669 to 1-652 --- 1-671; S.G. 3-05 to 3-10; H. 7.5; Monoclinic; Colours pale green, pale blue and colourless; Localities, Brazil and Russia.
- Euhedral crystals crystals which show good faces and form.
- "Evening Emerald" MISNOMER ( COMMERCIAL LABEL ) for peridot.
- Extinction when a doubly refracting crystal is viewed in parallel polarised light with the Nicol prisms (or "Polaroid" discs) crossed, on rotation of the stage, the field becomes four times light and four times dark, i.e., extinction at 90 degrees. With isotropic materials the field remains dark at all positions. Isotropic material, when under strain, may show anomalous extinction but rarely orientated at 90 degrees. (Anomalous double refraction.)
- Extraordinary ray that ray in a doubly refracting uniaxial mineral in which the velocity varies according to the direction in which it passes through the crystal.
- Eyed agate agate in which the coloured bands are circularly arranged in such a way that they resemble an eye.