EMERAUDINE :
Prohibited appellation for a Dioptase.

EMERI :
French for emery.

EMERITA :
Commercial name for an imitation emerald ; made by starting with a nodule of colourless or very pale beryl, recovered with synthetic material fabricated by Lechleitner, and also called Symerald.
Physical and optical properties:
- Colours and Hardness more or less identical with those of natural emeralds.
- S.G. : 2.649 to 2.713
- R.I. : 1.571 - 1.590 (Birefr. : 0.007)
See also :
- Emerita - Symerald (ZDG n°49 , 1964, page 37).
- Untersuchung von Sandwich Smaragd (Lechleitner - Emerita), by Verena Theisen (ZDG n°56, 1966, page 18).

EMERY :
An impure variety of Corundum serving as an abrasive.

EMILDINE :
Name given in South Africa to a variety of Spessartite.

EMILITE :
Synonym for Emildine.

ENAMEL :
Vitreous opaque or semi-opaque composition applied by fusion on metals and sometimes employed in the past to imitate gemstones.

ENDIOPSIDE :
Mineral of  intermediate composition between Enstatite and Diopside.

ENDURA EMERALD :
Commercial name given to a glass employed, among others, as an imitation for emerald.

ENGELHEARDITE :
Octahedron variety of Zircon.

ENHYDRE :
Or Enhydros.
Chalcedony containing a droplet of water.

ENSTATITE :
Belongs to the group of the  pyroxenes.
Mg₂[Si₂O₆]
Silicate of magnesium.
Physical and optical properties:
- Colours : brownish green, green, grey, yellowish, white-greyish, red-brown, blackish, bronze,
- Transparency : transparent to opaque
- Lustre : vitreous
- Hardness : 5.5 (superior to those of other pyroxenes).
- S.G. : 3.20 to 3.30 (that augments with the iron content).
- R.I. : 1.658 (+0.020 / –0.001) - 1.668 (+0.022 /-0.001) (augmenting also with the iron content) (Birefr : 0.009 to 0.012).
- Biaxial positive.
- Crystal system : orthorhombic according to Lapadu and Webster, (monoclinic according to Liddicoat).
- Dichroism distinct : green - yellow green.
- The spectrum shows a line in the blue towards 505 nm.
- Fluorescence : none.
- Cleavage : easy.
The optical sign and the value of the birefringence are the only elements for distinguishing enstatite and bronzite from kornerupine (biaxial negative).

Can present the optical effect of cat’s eye when cut as a cabochon due to needle-like mineral inclusions.
Occurrences :
Is found together with olivine and spinel in, for example, the kimberlites of South Africa or in  gem-bearing gravels.
Madagascar, Sri Lanka.
See also :
- Stern-Diopside und Stern-Enstatite, by Prof. W.F. Eppler (ZDG n°62 , 1967, page 55).
- Some materials, by W.F. Eppler (TJG Vol.12 n)7 de 1971, page 259).

EOSITE :
Vanado-molybdate of lead, also called "Stone of Tibet".
Pb(Mo,V)O₄
Colours : white, pink, red.
See also :
- Nouvelles du Laboratoire (Technica n°322 , May 1973).

EOSPHORITE :
Collector’s stone.
(Mn₂₊,Fe₂₊)Al(OH)₂PO₄.H₂O
Physical and optical properties:
- Colours : colourless, yellowish, brownish pink, light pink
- Transparency : transparent to translucent
- Lustre : vitreous
- Hardness : 5
- S.G. : 3.06
- R.I. : 1.640 - 1.668 (+0.003) (birefr. : 0.028 to 0.032)
- Biaxial negative.

- Crystal system : orthorhombic
- Two absorption lines at 410 and 490 nm.
Confusions :
- Kunzite.
See also :
Eosphorite (Gems & Gemology Fall 1970, vol. XIII n°7)

EPIDOTE :
Synonym : Pistacite, Pistachite, Piztazite.
Silicate of calcium, aluminium and iron.
Ca₂(Al,Fe)₃Si₃O₁₂(OH)
Physical and optical properties:
- Colours : different shades of green and brown, black, white, yellowish, pink
- Transparency : Transparent
- Lustre :  vitreous
- Hardness : 6 to 7
- S.G. : 3.4
- R.I. : 1.729 - 1.768 (+0.012 / -0.035) (Birefr : 0.019 to 0.051)
- Biaxial negative, certain minerals of a high index are biaxial positive.
- Crystal system monoclinic.
- Pleochroism : strong : green/brown/yellow.
- Spectrum : only a central green-blue part is not absorbed.
- Cleavage : perfect parallel to base.
- Fracture : conchoidal.
- Fluorescence : none.
Occurrences :
France, Austria, Madagascar, Brazil, Sri Lanka, Switzerland, U.S.A., Myanmar, Norway..
Confusions :
Jade, vesiuvanite (= idocrase), tsavorite (isotropic).
The different varieties :
- Clesozoisite is a variety of light green to brown-green epidote poor in iron-content.
- Piemontite is a variety of opaque copper-red epidote.
- Saussurite is an association of epidote-albite-chlorite.
- Unakite is an association of green epidote and pink feldspar.
See also :
Der Group von Epidotes, by Verena Theisen (ZDG n°48 , 1964, page 24)

(ALUMINOUS) EPIDOTE :
See Clinozoïsite.

EPIPHOSPHORITE :
Variety of Apatite.

ERDMANNITE :
Variety of ferrous Zircon.
Designates also a variety of Ortite.

ERINIDE :
Or Erinite.
Commercial name for a  synthetic spinel of green-yellow colour imitating a Peridot.

ERLANE :
Variety of compact de Grossular Garnet.

ERNITE :
Synonym of Grossular Garnet.

ESCARBILLE DE CHAUX :
French. Variety of calcareous Alabaster and it is forbidden to sell it under the name Onyx.

ESCARBOUCLE :
French term given in the Middle Ages to red stones principally to the red Almandine Garnet.

ESCHERITE :
Variety of Epidote.

ESSIG SPINEL :
German. Synonym of Rubicelle (French).

ESSONITE :
Synonym of Hessonite. 

ESRAMADURITE :
Variety of Agate.

EUBAN :
Variety of Quartz.

EUCLASE :
Basic silicate of aluminium and beryllium.
BeAl[SiO₄]OH
Physical and optical properties:
- Colours : light blue to colourless, blue-green, ocean blue, violet (very rare)
- Transparency : Transparent to translucent
- Lustre : vitreous
- Hardness : 7.5
- S.G. : 3.05 to 3.13
- R.I. : 1.650 (+0.004) - 1.672 (+0.004/-0.003) (Birefr : +0.019 to +0.025)
- Biaxial positive.
- Dichroism : weak.
- U.V. : very weak luminescence
.- Crystal system : monoclinic
- Spectrum : absorption band in the blue-violet + line in the red (705nm double, 468nm weak, 455 weak).
- Cleavage : perfect and easy.
- Fracture : conchoidal.
- Appears greenish under the Chelsea filter.
- Becomes electrically charged when rubbed.
Occurrences :
Colombia, Brazil (Ouro Pretro, Minas Gerais), Zimbabwe, India, Tanzania (Morodoro), Austria.
Mineral of pegmatites sometimes associated to beryl and to topaz.
Also product of secondary deposits and found as a geode.
Confusions :
- Phenacite (S.G. : 2.96 ; R.I. : 1.65 to 1.67 ; uniaxial, colourless).
- Spodumene light green (S.G. : 3.2 ; R.I. : 1.66 to 1.68).
- Topaz blue (S.G. : 3.56 ; R.I. : 1.62).
- Aquamarine (S.G.: 2.7 to 2.8; R.I.: 1.57 to 1.59; uniaxial, often pure).
- Synthetic Spinel light blue (S.G. : 3.65 ; R.I. 1.73 ; isotropic, red under the Chelsea filter).
- Glass (S.G. & R.I. variable ; isotropic).
Treatments :
The colour of pale euclase may be enhanced by irradiation.

EUCOLITE :
Eucolite is an Eudialyte rich in calcium and containing Nb. (See Eudialyte)
Physical and optical properties:
- Colours : brown to vivid red.
- S.G. : 3
- R.I. : 1.634 - 1.643 (Birefr. : -0.009)
- Uniaxial negative.
Occurrences :
- Langesundfjord in Norway
- Magnet Cove in U.S.A.
- Madagascar

EUDIALYTE :
Collector’s stone
(Na,Ca,Fe)₆Zr[(OH,Cl)|(Si₃O₉)₂].
Physical and optical properties:
- Colours : yellowish brown, yellowish red, pink to vivid red, vitreous lustre.
- Hardness : 5 to 6
- S.G. : 2.88 to 3
- R.I. : 1.593 - 1.613 (Birefr. : +0.004)
- Uniaxial positive.
- Crystal system : trigonal.
Occurrences :
- Kola and Lujarre in Russia.
- Julianehaab and Norra Kärr in Greenland.
- Magnet Cove in U.S.A.
- Mont Saint Hilaire in Canada.
- Pilansberg in South Africa

EULYSITE :
Peridot ferriferous.

EUXINITE :
Collector’s stone
(Y,Ce,U,Pb,Ca)(Nb,Ta,Ti)₂(O,OH)₆
Physical and optical properties:
- Colours :  brownish grey to black
- Transparency : opaque
- Lustre : metallic lustre
- Hardness : 5.5 to 6.5
- S.G. : 4.7 to 5.0
- R.I. : 2.06 - 2.26
- Crystal system : orthorhombic
Occurrences :
Madagascar, Norway, Brazil, Finland, Canada, U.S.A., Australia.

EYE-OF-THE-WORLD :
Synonym of Opal.

EZTERI :
Jasper , green with red veins (term given by the Spanish speaking Americans).