FABULITE :
Or Strontium Titanate.
Synonyms : Starilian or Symant.
Synthetic Product, imitating diamond.
SrTiO₃, titanate of strontium.
Physical and optical properties :
- Colours : colourless (colour D in diamond grading table)
- Transparency : Transparent
- Hardness : 5 to 6
- S.G. : 5.13
- R.I. : 2.41
- System : cubic
See also :
- Fabulite Doublets (Gems & Gemology, Fall 1971 Vol. XIII, n°11).
- Ein neues Doublet als Diamantimitation (ZDG n°53 , 1965, page 56).
- Dispersion von Fabulite, Strontium Titanate (ZDG n°59 , 1967, page 16).
- Modern Synthetic Gemstones, by R. Webster (TJG Vol. 12 n°4 , 1970, page 139).
- Titania et Fabulite (TEC n°138, 1958, page 22).
- La Fabulite, by Prof. Dr. Schlossmacher (TEC n°152 , 1959, page 143).

FAHLUNGRANAT :
German. Synonym of Almandine Garnet.

FAIRY STONE :
English Term for the French name Pierre de Fée. Used as a synonym for a staurotide or a twinned variety of staurotide .

FALKENAUGE :
German term for the French name Œil-de-Faucon. (English term is Hawk’s eye).

FASHODA RUBY :
See Ruby Fashoda.

FAUSSE AMETHYSTE :
French term. Prohibited appellation for a violet Fluorite.

FAUSSE CHRYSOLITE :
French term. Prohibited appellation for a Moldavite.

FAUSSE EMERAUDE :
French term.  Prohibited appellation for a green Fluorite.

FAUSSE HYACINTHE :
French term.  Prohibited appellation . Formerly hyacinth meant a Hessonite garnet, now applied to the reddish brown zircon.

FAUSSE TOPAZE :
French term.  Prohibited appellation for a yellow fluorite or for a citrine.

FAUX LAPIS :
French term used for German Lapis or Swiss lapis (= both terms used for died jasper).

FAUX SAPPHIRE :
French term.  Prohibited appellation for a blue Fluorite.

FAYALITE :
Name given by the English to a variety of ferrous Peridot from Fayal (Açores), opaque and black. It’s surface is sometimes brown and iridescent.
Fe₂SiO₄.

FEDERGIPS :
German term for Feather Gypsum (also in German : Fasergips).
German Term for satin Spar or fibrous Gypsum.

FEIJAO :
Brazilian name. Variety of black Tourmaline from Brazil.

FEITSUI :
Or Fei Ts'ui (“fei cui”) Chinese term. Translation = ‘not true jade’ (although applied to real jadeite).
Synonym of Jadeite.
Name given by the Chinese to a -for them new type- of Jade coming from the jadeite deposits in Burma and that was imported to China only from the middle of the 18^th century onward in large quantities (before, the Chinese had no access to this source of ‘jade’ and in the beginning the material was regarded suspiciously hence the name : ‘not real jade’), having -in the best qualities- the colour of the back-feathers of the Kingfisher bird : a blue-green brilliant colour ; more recently also applied to Jadeite in general.

FELDSPAR :
Group of silicates of aluminium, of calcium, of potassium and of sodium.
Stones belonging to the group of the feldspars :
Amazonite, Orthose, Moonstone, Sun Stone, Spectrolite, Labradorite, etc.
The stones of this group are the most abundant of the earth’s crest.
Physical and optical properties :
- Colours : divers tints going from white to sometimes very pinkish to grey, yellow, green ; Certain feldspars display an iridescence coupled with vivid colours.  This phenomenon is called labradorisation and is thus typical for labradorite but may also occur in orthose, anderite, oligoclase, adularia, anorthite, etc.
- The gem variety of respectively adularia is called Moonstone, of oligoclase Sun Stone and of microcline Amazonite.
- Hardness : 6
- S.G. : 2.56 to 2.70
- R.I. : 1.52 - 1.54 (Birefr : +0.008)
- Dichroism : none.
- Cleavage : easy.
- System monoclinic (sanidine, orthose, celsian, hylophane) or triclinic (microcline, albite, oligoclase, andesite, labradorite, anorthite).
Occurrences :
Madagascar (orthose of pale yellow colour).
Treatments :
It is possible to encounter feldspars dyed blue to imitate lapis-lazuli.
See also :
- Feldspat, by Elisabeth Strack (ZDG n°55 , 1966, page 30).
- Helbrauner klar durchsichtiger Alkalifeldspat von Volkesfeld-Eifel, by H. Bank and M. Okrusch (ZDG n°61 , 1967, page 50).
- Les feldspaths, by Pierre Van de Walle (TEC n°253 , 1967, page 513).
- Durchsichtiger blassgelblicher Plagioklas aus den U.S.A., by H. Bank (ZDG 19 , 1970 n°3/4, page 134).

(BLUE) FELDSPAR :
Synonym of Lazulite.

(NACREOUS) FELDSPAR :
Synonym of Moonstone.

(TENACEOUS) FELDSPAR :
Synonym of Saussurite.

FELDSPAR APYRE :
Synonym of Andalousite.

FELDSPAT :
German name for Feldspar

FELSENRUBIN :
German term. Prohibited Appellation for a Pyrope or Almandine Garnet.

FEMALE :
Adjective used formerly to designate gemstones of light colours (female sapphire : a light blue sapphire, “female ruby” : a pink coloured or very pale ruby). Prohibited Appellation.

FEMELLE :
French or Female.
Prohibited Appellation.

FER AZUR :
French term. Synonym for Vivianite.

FER OLIGISITE :
French term. Synonym for Hematite.

FER OXYDE ROUGE :
French term. Synonym for Hematite.

FER PHOSPHATE :
French term. Synonym for Vivianite.

FER SPECULAIRE :
French term. Synonym for Hematite.

FER SULFURE :
Synonym for Pyrite.

FEROZAH :
Or Firozah, or Firuza ;
Persian term for Turquoise (Meaning :  Victorious).

FERROPICOTITE :
French term. Spinel with in its composition chrome is replaced by iron.

FETTBOL :
German term. Synonym of Chloropal.

FEUEROPAL :
German term for a Fire Opal.

FIBROLITE :
Synonym for Sillimanite.
Silicate of aluminium.
Al₂SiO₅
Physical and optical properties :
- Colours : white, grey, yellow, greenish, blue, blue-green, red, brown.
- Hardness : 6 to 7.5
- S.G. : 3.17 to 3.24
- R.I. : 1.659 - 1.680 (Birefr. : 0.019)
- Uniaxial positive.
- System orthorhombic.

FIGURE STONE :
English Name for Agalmatolite.

FIORITE :
Variety of common Opal having a lustre like that of a pearl.

FIRE OPAL :
Variety of opal almost exclusively coming from Mexico; it does not generally have an opalescent effect (= does not show a play of colours)
- Colours : yellow, yellow-orange, brown-red, red
- Hardness : 6
- R.I.: 1.45
- S.G. : 2.0

FIRESTONE :
Name given by the English to a Quartz artificially cracked by heat to obtain an iridescent effect.

FIRMAMENT STONE :
Synonym of precious Opal.

FIRUZEGI :
Synonym of Turquoise.

FISCHAUGE :
German term. Synonym of Fish Eye, or Moonstone.
Term equally employed for an Opal Girasol.

FLECHES D’AMOUR :
French term. Hyalin Quartz with as inclusions lots of needles of rutile.
Equally previously used in Russia to designate an Amethyst containing needles of Goethite.

FLINT GLASS :
Glass containing lead oxides and sometimes used as an imitation for gemstones.
Physical and optical properties :
- Colours : Divers.
- Hardness : 5
- S.G. : 2.9 to 5.0
- R.I. : 1.54 to 1.78

FLOWERING OBSIDIAN :
Name given by the Americans to a variety of Obsidian from Oregon presenting the colours red, brown-red flecked by black, golden, silver-grey, acajou.

FLUORAPATITE :
Variety of fluorine-containing Apatite.

FLUORITE :
Or Fluorine, Fluor-Spar.
Fluoride of calcium.
CaF₂.
Physical and optical properties :
- Colours : Colourless when pure, green, sometimes orange, blue, light violet to dark violet, pink, red. The colour is in all cases distributed in a way of zonations parallel to the faces of the cube or of the octahedron.
- Hardness : 4
- P.S : 3 to 3.5
- R.I. : 1.434 ; birefringence : none (but may sometimes present an abnormal birefringence).
- System : cubic.
- Cleavage perfect following the octahedron.
- Fluorescence : generally strong, blue-violet.
Inclusions :
healing fractures, negative crystals filled with saline water and gas presenting typical forms derived from the cube (octahedron, tetrahedron,…).
Pyrite may be included in the crystal.
Inclusions in the form of a net.
Treatments :
Iradiation of fluorite can enhance its colour.
Occurences :
Abundant in hydrothermal veins of blende, galena, pyrite. May accompany baryte.
Fluorite is present in the whole world, examples :
- Cumberland, Switzerland, U.S.A., Canada, Germany, Spain, Italy, Norway, Australia
Confusions :
- Amethyst (S.G. : 2.65 ; R.I. : 1.545 to 1.555)
- Emerald (S.G. : 2.70 ; R.I. : 1.57).
- Glass (S.G. variable ; R.I. : superior to 1.48)
Imitations :
Glass.
Synthetics :
See" synthetic fluorite ".
See also :
- Beitrag zum Farb- und Lumineszenzproblem des Fluorits, by A. Neuhaus, K. Recker and R. Leckebusch. ( ZDG n°61 , 1967, page 89).
- La Fluorite, by M. Hemon & H.J. Schubnel ( AFG n°12, page 7).
- Synthèse de la Fluorine, by F. Duyk (AFG n°25, page 12).
- Modern Synthetic Gemstones, by R. Webster (TJG Vol.12 n°4 , 1970, page 119).
- Synthèse de la Fluorine, by F. Duyk (TJG Vol.12 n°6 , 1971, page 209).
- L'exploitation du " Blue John " dans les collines du Derbyshire, H. Mornard (TEC n°301 , 1971, page 405).

FLUOR DORE :
French term. Or Gold Fluss.
See Aventurine, Aventurine Feldspar or Sun Stone (and Gold Fluss).

FLUSSPATH :
German term. Synonym of Fluorite.

FORSTERITE :
Name given by the English to a variety of Peridot with a very high magnesium content.
Mg₂SiO₄

FORSCHERITE :
Or Forcherite.
Variety of Opal.

FOSSIL CORAL :
See Beekite.

FOSSIL TURQUOISE :

Prohibited Appellation for odontolite .

FOWLERITE :
Variety of Rhodonite of brownish colour, of Sussex Co., in New Jersey.

FREMY RUBIS :
French. Name given to the flux synthetic ruby fabricated by the French chemist Frémy.

FRENCH SAPPHIRE

FRESNOITE :
In its 50 years of existence the GIA got only one fresnoite to examine up to now. This stone of yellow to peach colour, very rare, owns its name to the town of Fresno in California where it was discovered for the first time.
The one examined by GIA came from the Junnila mine in the County of San Benito in California, at a short distance only from the famous mine of benitoite.
Fresnoite is a Silicate of barium and  titanium, tetragonal, of yellow to peach colour.
The rare examples known don’t exceed 2 ct.
Ba₂TiSi₂O₈
R.I. : 1.765 – 1.773 (Birefr. : 0.008).
S.G. : 4.5 to 4.6
There exists a synthesized  version obtained by the Czochralski method, but the total absence of inclusions are the elements of identification, where the natural stones present numerous inclusions under the form of " finger prints" and libellae. (Sources : G & G Autumn 2000)

FRIABLE AMBER :
English Name for Gedanite.

FRIEDELITE :
Etym. : dedicated to Ch. Friedel (France, 1832 - 1899).
H₇(Mn,Cl)Mn₄,Si₄O₁₆.
Collector’s stone, very rare.
Physical and optical properties :
- Colours : ; pink-red, red-orange, reddish brown ;.
- transparency : translucent
- lustre : vitreous, slightly nacreous
- Hardness : 4 to 5
- S.G. : 3.04 to 3.07
- R.I. : 1.62 - 1.656 (Birefr. : -0.030 to -0.036)
- Uniaxial negative.
- Crystal System : trigonal.
- Cleavage : quite good.
- Fluorescence : dark red and sometimes yellow under U.V.L., sometimes green under U.V.S.
- Red under Chelsea filter.
- Spectrum : a large band around 556nm and a weak band at 456nm.
Occurences :
- Franklin Furnace in New Jersey, U.S.A.
- Mine of Adervielle in the valley of Louron in the Hautes Pyrénées in France.
- Wermland in Sweden.
- Eureka in Colorado, U.S.A..
- Kyurazawa Mine at Togichi in Japan.
- South Africa.

FUCHSITE :
Green Mica found as an inclusion in aventurine Quartz (chromiferous mica).

FUGITIVE OPAL :
Variety of opal showing red flames all of a sudden that disappear as soon as they appeared.

FULGURITE :
Synonym for Lechatelierite or silica-glass
SiO₂  , vitreous phase
“Mother Nature makes glass each time a large amount of energy is released during a sufficient period of time at the Earth's surface, provided that the soil composition is suitable for making glass. The latter condition is satisfied, for example, by sandy soil, with the resultant natural glass being silica glass named "lechatelierite" after the French chemist Henry Le Châtelier (1850-1936). There are two phenomena that are responsible for making natural glass on Earth: meteorites and lightning. Glass that is made as a result of the collision of a meteorite with the Earth's surface is called meteoritic glass or tektite. Glass (a glassy object, to be exact) that is made as a result of a cloud-to-ground lightning discharge is called a fulgurite (from the Latin "fulgur" which means lightning). Fulgurites come in a great variety of forms and can be viewed as nature's own works of art. It is worth noting that lechatelierite (natural silica glass) is not present in obsidian, a glass-like material associated with volcanic activity. On the other hand, volcanic activity is known to generate lightning which, if it strikes sandy soil, may produce a fulgurite. Silica glass has been also made as a result of nuclear explosions. In 1945, the first nuclear bomb (equivalent to 18,000 tons of TNT) was detonated in the New Mexico desert. The explosion formed a crater 800 yards in diameter, glazed with a dull gray-green silica glass. This glass was named "trinitite" after Trinity Site where the first nuclear bomb test was conducted.”

Extract from ‘LIGHTNING MAKES GLASS’ by Vladimir A. Rakov , 29th Annual Conference of the Glass Art Society, Tampa, Florida, 1999 .

See also :
Odontolite and Fulgurite, by G. V. Axon, TJG, Vol.12 n°5 , 1971, page 171.

FUNKITE :
Variety of Diopside.

FUSCITE :
Synonym of Scapolite.

FUTURAN :
Commercial name for a plastic composed of phenol aldehyde, used to imitate amber .