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IASPIS :
Ancient orthograph for Jasper.
ICELAND AGATE :
Prohibited Appellation for a brownish or greyish obsidian.
ICELAND SPAR :
English Name for a calcite from Iceland.
ICE SPAR :
Synonym of sanidine.
ICE STONE :
Name given by the Ojibway Indians of America to white stones.
From there, equally applied to Rock crystal.
ICHTYOPHTHALME :
Or Ichtyophthalmite.
Synonym of Apophyllite.
IDOCRASE :
Or Vesuvianite, (Vésuvienne in French)
Etym. : named after Mount Vesuvius, Italy, where it
was first found
Complicated calcium aluminium silicate
Ca10(Mg,Fe)2Al4(OH)4/(SiO4)5/(Si2O7)2
Varieties : californite , cyprine, xanthite, wiluite
Physical and optical properties :
- Colours : yellow-green to pistache green, brown of different nuances,
rarely bluish or pink or colourless.
- Transparency : transparent to translucent
- Hardness : 5.5 to 7
- S.G. : 3.30 to 3.50
- R.I. : 1,700 – 1.710 to 1.721 – 1.723 (Birefr. : 0.001
to 0.010).
- Uniaxial negative.
- System : tetragonal.
Occurrences :
Canada, Russia, USA, Italy
IGMERALD :
Commercial Name for a synthetic emerald fabricated by I.G. Farben industry in
Germany already before the 2nd World War.
ILLUDERITE :
Synonym of Zoisite.
ILMENITE :
Oxide of titanium with up to about 6 % of Fe2O3.
FeTiO3
Physical and optical properties :
- Colours : black.
- Transparency : opaque
- Hardness : 5 to 6
- S.G. : 4.5 to 5
- System : hexagonal.
IMAGE STONE :
English Name for an agalmatolite.
IMPERIAL JADE :
Name given to jadeite of emerald green colour (from Burma).
IMPERIAL MEXICAN JADE :
Prohibited Appellation for a green Calcite.
IMPERIAL YU-STONE :
Name given in the Orient (especially China) to a green aventurine quartz.
INANGA :
Name given by the Maori people to a variety of different local nephrite varieties of grey colour.
INCA PINK :
Argentina Term for a Rhodocrosite.
INCA STONE :
Synonym of Pyrite.
INDIAN AGATE :
Name serving to designate the Stone of Mocha, or moss agate, equally dendritic Agate.
INDIAN EMERALD :
Prohibited Appellation for a green sapphire or correctly an emerald from
India.
INDIAN JADE :
Prohibited Appellation serving to designate an aventurine quartz.
INDICOLITE :
Synonym for indigolite.
INDIGOLITE :
Synonym of Indicolite. Variety of lithic, dark blue tourmaline ranging in colour from
blue-blackish, blue violet to blue-greenish.
INDIGO SAPPHIRE :
Variety of sapphire of a very dark blue colour.
INDIVISIBLE QUARTZ :
Synonym of Opal.
INKY SAPPHIRE :
Variety of Sapphire of a very dark blue colour.
INTAGLIO :
Stone ( generally onyx Agate, Carnelian or Chalcedony)
cut and engraved in dept to serve as seal.
INTAILLE :
French for Intaglio.
INVELITE :
Plastic material similar to Bakelite.
INVERELL SAPPHIRE :
Commercial Name for a local mineral of Crooked River, Oregon, resembling to a
rubanated red Jasper.
IOLITE
:
Synonyms : cordierite or dichroite
Silicate
of aluminium ad magnesium.
Mg2Al3[Al Si5
O18]
Physical and optical properties:
- Colours : divers tones of blue (light blue, intense blue with a touch
of violet), brownish.
-
Transparency : transparent to translucent
-
Lustre : vitreous to greasy
- Hardness : 7 to 7.5
- S.G. : 2.57 to 2.66
- R.I. : 1.542 - 1.551 (Birefr : 0.006 to 0.016)
- Biaxial negative.
- System : orthorhombic, pseudo-hexagonal.
- Strongly dichroic, visible to the naked eye : blue – dark violet
- pale blue.
- Cleavage axial net to imperfect and basal separation plan.
- Spectrum : absorption band in the red comprising also the orange +
band in the violet up to the indigo + lines in the blue, in the green
and 2 in the yellow.
- Fluorescence : none.
The stone is cut in such a way that the table is perpendicular to the
direction of principal absorption (giving the blue, perpendicular to the pseudo hexagonal axis of the crystal).
Occurrences :
Classical constituent of schist rocks and gneisses having undergone
a contact metamorphism.
Granites and pegmatitic granites, often associated with andalusite,
spinel ad corundum.
Sri Lanka, Norway, Brazil, India, Madagascar, Sri Lanka, Canada, South-West
Africa.
Imitations :
- Glass (S.G. & R.I. variables ; gas bubbles).
- Corundum synthetic (S.G. : 4 ; R.I. : 1.77
; curved zones of coloration and curved growth lines).
Inclusions :
Divers colourless or brownish open fractures containing sometimes rather
dark dendrites.
Lamellar inclusions of greenish mica, crystals of goethite in the form
of hexagonal platelets, of hematite or of rutile are also visible in
certain cases.
Eventually inclusions of monazite with radioactive halo.
Occurrences :
Sri Lanka (colour blue-violet to grey), India, Myanmar, Madagascar,
Canada, California.
Confusions :
The most probable confusions are all the blue stones.
- Benitoite (S.G. : 3.67 ; R.I. : 1.757 and 1.804 ; dichroism : blue and whitish).
- Sapphire (S.G. : 3.99 ; R.I. : 1.76 to 1.77 ; healing fractures like wings)
- Spinel blue to violet (S.G. : 3.65 ; R.I. : 1.71 to 1.72 ; isotropic).
- Tanzanite (S.G. : 3.3 ; R.I. : 1.70 to 1.71 ; strongly dichroic).
- Tourmaline blue (= Indigolite) or violet (S.G. 3 to 3.2 ; R.I. : 1.62 to 1.64 ;
medium dichroic)
- Amethyst (S.G. : 2.65 ; R.I. : 1.54 to 1.55 ; optical and physical characteristics
the closest of all possible confusions but amethyst is more pure violet
in colour).
See also :
- Cordierite (ZDG n°43 , 1963, page 21).
- Note sur les Cordiérites par H. J. Schubnel (AFG n°21, page 12).
- Cordiérite ou iolite (TEC n°163 of 1960, page 82).
IRIDOT :
Name given to opal around 1880.
IRIS :
Variety of quartz rainbow coloured, showing beautiful reflections of colours.
IRISH DIAMOND :
Prohibited Appellation for a rock crystal.
(BLUE) IRONSTONE :
Synonym of Vivianite.
ISLE OF WIGHT DIAMOND :
Prohibited Appellation for a rock crystal.
ISOLITE :
Synonym of Cordierite.
ISOPYRE :
Impure Variety of Opal.
ITATLI :
Aztec Name for Obsidian. Synonym also Iztli.
IVAARITE :
Titaniferous Garnet, related to Schorlomite.
IVORY :
Phosphated secretion constituting the tusks of the elephant.
If the material comes from another animal, its nature has to be specified.
Ca3OH)2(PO4)6Ca4
Physical and optical properties :
- Colour : opaque ; creamy white, yellowish white.
- Hardness : 2.5 to 2.75
- R.I. : 1.54
- S.G. : 1.70 to 195 (but never 2).
- Fluorescence : different hues of blue.
Occurrences :
Africa, Myanmar, India, Sumatra.
Treatments :
- Old ivory being more appreciated than new ivory, artificial aging
is a treatment frequently used (treatment in tea, brownishing with the
smoke of incense). The use of oil is equally used to give a patina to
the ivory when polishing.
- The powder and the fragments of ivory produced when cutting serve
to fabricate the black of ivory by combustion.
- Ivory may be tinted with the aid of divers metallic salts or organic
materials.
Imitations :
- The most convincing imitation is the one produced by plaques of celluloid
correctly arranged, and assembled under pressure.
- Plastics and moulds of plaster of suitable colour, treated with a
product based on wax.
Confusions :
Bone, wood, corozo (fruit which, when mature, becomes milky, then solid
and whitish), different kinds of tooth, the horned casque of the Kakatoe.
IVORY TURQUOISE :
English Name for Odontolite.
IWAARITE :
Synonym of Ivaarite.
IZTAC CHALCHIHUITE :
Mexican Onyx, white and green.
IZTLI :
Aztec Name for Obsidian.
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