DALLASITE :
Name given by the Americans to a green and white Jasper found in the Dallas Mountains, in British Colombia.

DAMMSTEIN :
German. Synonym of Amber.

DANBURITE :
Collector’s stone.
Borosilicate of calcium.
CaB₂(SiO₄)₂
Physical and optical properties:
- Colours : most often colourless, but also yellow, pink, yellow-orange, brownish yellow, greyish.
- Transparency : Transparent
- Lustre : vitreous
- Hardness : 7 to 7.5
- S.G. : 3
- R.I. : 1.630 - 1.636 (Birefr. : - 0.006).
- Biaxial negative.
- System orthorhombic
- Spectrum of rare earth elements (like yellow apatite).
Occurrences :
Encountered in gem bearing gravels.
Sri Lanka, Japan, Mexico, Madagascar, Myanmar (Mogok).
Confusions :
- Topaz (S.G. : 3.56 ; R.I. : 1.62 to 1.63)
- Apatite (S.G. : 3.2 ; R.I. : 1.63 ; spectrum of rare earth elements, fines lines in the yellow and the green).
- Glass (S.G. : 3.7 ; R.I. variable ; bubbles and traces of fusion).
- Brazilianite ( S.G. : 2.98 ; R.I. : 1.60 to 1.62 ; very rare).
- Tourmaline (S.G. : 3.1 ; R.I. : 1.62 to 1.64).
- Citrine (S.G. : 2.65 ; R.I. : 1.54 to 1.55).
Remarks :
Danburyite or Danburyte are two terms erroneously used to designate a synthetic corundum of orange to pale red colour.
See also :
- Danburite aus Mexico (ZDG n°56 of 1966 page34)
- Danburite aus Mexico (ZDG n°58 of 1966 page 28)

DAOURITE :
lithic tourmaline of blood red colour (rubellite).

DARLINGITE :
Variety of Jasper.

DARWIN GLASS :
Etym. : from the location Mount Darwin (first scientifically recorded in 1927).

Kind of natural glass from near Mount Darwin in Tasmania, rich in silicon.

Closely related to Lybian glass; it is a meteorite crater glass, formed due to a meteorite impact; little different in composition from tektites .
Physical and optical properties:
- Colours : greyish green
- Transparency : opaque, slightly translucent on the borders
- S.G. : 1.8 to 2.3

DATHOLITE :
Or datolite. Collector’s stone.
Ca(B.OH)SiO₄
Physical and optical properties:
- Colours : milky white to brown-orangy, colourless, yellowish, violet, reddish, greenish, brownish.
- Transparency : transparent to opaque
- Hardness : 5 to 5.5
- S.G. : 2.9 to 3
- R.I. : 1.624 - 1.670 (Birefr. : -0.044).
- Biaxial negative.
- Crystal System : monoclinic.
- Cleavage none.
Occurrences :
Austria, U.S.A., Great Britain.
Confusion :
Danburite (S.G. : 3 ; R.I. 1.630 to 1.636)

DAUPHINITE :
Synonym of Anastase.

DAURITE :
Deformed orthographe of the term Daourite.

DAVIDSONITE :
Variety of Beryl of greenish yellow colour.

DEKOLITE :
Synonym for Bakelite.

DELAFOSSITE :
Spinel variety, containing copper.

DELATYNITE :
Or Delatinite.
Variety of amber found at Delatyn in the Carpathian mountains, Galicia, Ukraine.

A variety rich in carbon, low in succinic acid and quite free from S.

Physical and optical properties:
- Hardness : 2 to 2.5
- S.G. : 1.0444

DELAWARITE :
Variety of orthose of green aventurine colour found in Delaware County in Pennsylvania, U.S.A.

DELPHINITE :
Epidote of the Dauphiné, France, having a yellowish green colour.

DELVAUXENE :
Or Delvauxite.
Variety of Dufrenite.

DEMANTOID :
Etym. : from the old Flemish word ‘demant’ meaning ‘diamond’ because of the lustre of demantoid.

Belonging to the group of the Garnets, variety of Andradite.
= chromiferous Andradite of green colour (top quality, emerald green).
Ca₃Fe₂[SiO₄]₃
Demantoid is the most precious of the garnets. Only found as small crystals (rarely over 1 to 2 ct).
Physical and optical properties:
- Colours : grass green to emerald green, yellowish green, olive green brownish, green
- Transparency : Transparent
- Lustre : very vivid, adamantine
- Hardness : 6.5
- S.G. : 3.82 to 3.90
- R.I. : 1.888 to 1.889
- Crystal System cubic.
- Spectrum typical of chrome.
- Reddish under Chelsea filter.
Occurrences :
Italian Alps, Urals, Africa, Korea.
In sites riche in chrome.
Inclusions :
Demantoid from the Urals (not necessarily from other locations) almost always presents fibres of Chrysotile (asbestos) in the form of a horse-tail.
Confusions :
- Diamond green (S.G. : 3.52 ; R.I. : 2.418 ; stays green under Chelsea).
- Zircon green (S.G. : 4 ; R.I. : 1.85 to 1.90 ; reddish under Chelsea, spectrum typical of low zircon).
- Peridot = Olivine (S.G. : 3.35 ; R.I. 1.65 to 1.69 ; doubling of facet junctions very clearly visible).
- Hiddenite ( S.G. : 3.15 ; R.I. : 1.66 to 1.68)
- Tourmaline (S.G. : 3 to 3.2 ; R.I. : 1.62 to 1.64 ; ; doubling of facets is masked in green tourmaline because of the strong absorption of the ordinary ray).
- Emerald (S.G. : 2.7 ; R.I. : 1.57).

Supplementary information :                                                                                                            

DEMANTOÏDE :
French for demantoid.

DEMANTSPATH :
Old German synonym for Corundum.

DEMIDOFFITE :
Or Demidowite or Demidovite.
Mixture of Chrysocolla and a copper phosphate of blue colour.

DEMION :
Synonym of Cornelian.

DENDRITE :
Variety of pyrolusite (oxide of manganese), forming irregular designs in many minerals and notably in some Quartz.

DERBYSHIRE SPAR :
Name given by the English to a massive blue Fluorite.

DERBYSTONE :
Name given by the English to a Fluorite coloured artificially in amethyst colour.

DERMATINE :
Variety of Serpentine.

DESMINE :
Synonym of Stilbite

DESTINEZITE :
Variety of Dufrenite.

DEVIL’S STONE :

Synonym for peristerite.

DEVONSHIRE EMERALD :
Magnificent Emerald of intense grass green colour weighing 1383.95 cts, originating from the mines of Muzo, Columbia.
Offered in 1831 to the sixth Duke of Devonshire by Don Pedro (Emperor of Brazil).
Actually in the British Museum.

DEWEYLITE :
Two meanings possible for the term Deweylite :
- Ornamental stone, of reddish or light yellowish colour (Eppler).
- Amorphous mineral of the group of the serpentines (Dana ; S.G. : 2.00 to 2.2 ; Hardness : 2 to 3.5)

DIABASE :
Decorative stone of dark colour composed essentially of plagioclase and augite (group of the pyroxenes).

DIAKON :
Or Perpex.
Plastic material used in Great Britain to imitate Ivory.
Physical and optical properties:
- Colours :
- Hardness :
- S.G. : 1.50 (Anderson)
- R.I. : 1.50

DIALLAGE :
An old name referring to Amphibole, Pyroxene and/or Hypersthene.

(METALLOIDE) DIALLAGE :
Synonym of Bastite.

(GREEN) DIALLAGE :
Synonym of Smaragdite.

DIALLOGNON :
Synonym of Smaragdite.

DIALOGITE :
Or Diallogite.
Ancient Name for Rhodocrosite.

DIAMONAIR :
See also :
- Le " diamonair " (TEC n°284 of 1970, page 152).
- Le Diamonair, by F. Duyk (TEC n°298 of 1971, page 225).
- Diamonair (Publ. Question & Answer) (TEC n°313 of 1972, page 415).

DIAMOND :
Etym. : from the Greek ‘adamas’ meaning invincible Carbon.
C
Physical and optical properties:
- Colours : Colourless , all colours up to black (See for example pink diamond)
- Transparency : transparent
- Lustre : adamantine
- Hardness : 10
- S.G. : 3.52
- R.I. : 2.407 to 2.451
- Cleavage perfect.
- Crystal System cubic.
The atoms are linked by covalent bindings, the strongest binding.
Occurrences :
Alluvionnary sites, and in situ in kimberlites and lamproites.
India, North America, Russia, China, South America, Australia, … .
Supplementary information :                                                                                                            
Table of characteristics of diamond and of its principal imitations.

Synthetics :(See synthetic Diamond)
The fabrication of synthetic diamonds reposes on the natural crystallisation conditions of the stone, high temperature (1500 to 2000C°) and high pressure (50.000 to 100.000 atmospheres).
To favour crystallisation, iron, nickel, cobalt are necessary.
The synthetic diamonds are produced starting from graphite and carbon isotopes.
The method of fabrication of synthetics diamond uses temperatures between 1700 C° and 2760C° with pressure of 10 T/cm².
The stones produced can be coloured or colourless and vary between 0.5 ct and 1 ct.
Identification :
· Magnetism possible.
· Dark cross between polarising filter (false birefringence due to internal tensions).
· Spectrum : bands possible at 415,5 nm, between 658-637 nm and 560 to 460 nm.
· Metallic inclusions.
· No natural inclusions (like magnetite, chromite, pyrope, green diopside, enstatite, diamond octahedron ).
· Inclusions of " pinpoints ".
· Fluorescence under SWUV and very weak to none under LWUV.
· Possibility of slight phosphorescence.
Treatments :
Diamonds of poor quality can be heated to temperatures and pressures that are those of the natural formation of the stone (similar equipment used as for producing synthetic diamond). (treatment = called HPHT).
The treated stones can gain a better colour (in the white range) or a fancy colour, without other changes to hardness or density.
Ex : Diamond GE POL.
Supplementary information relative to treatments :
- A rough diamond of 13.12 carats of yellow colour identified after spectroscopic examination as having been treated in view of enhancing its colour.
The results obtained showed a strong absorption line at 415nm but absence of the band at 478nm (the last one being present in stones of natural colour).
A  pair of lines at 495 and 503 nm in association with a green luminescence is present in the stones of natural colour. In the present case, the luminescence was absent.
The treatment has been confirmed by other, more sophisticated instruments.

Confusions :
All  colourless gems. Topaz, zircon (colourless by thermal treatment), sapphire, sphalerite, sphene, cassiterite.
Imitations :
Glass doped with lead, colourless strass, doublets and divers triplets, synthetic corundums like colourless Verneuil, synthetic spinel, synthetic rutile, fabulite (=strontium titanate ), YAG, GGG, zirconium oxide.

Prohibited appellations : (V. Prohibited appellations)
- " diamond of Alaska " for black hematite or for rock crystal.
- " diamond of Alençon " for a (smoky) quartz or a rock crystal.
- " German diamond " for a smoky quartz.
- " diamond of the Alps " for a pyrite.
- " aluminium diamond "  pour synthetic corundum.
- " diamond of Arkansas " for quartz named also Horatio Diamond.
- " diamond of Bohemia " for a quartz.
- " diamond of Brazil " for a rock crystal, but may also designate the provenance of a natural diamond.
- " diamond of Briançon " for a quartz.
- " diamond of Brighton " fora quartz.
- " diamond of Bristol " for a quartz.
- " diamond of Buxton " for a quartz.
- " diamond of Sri Lanka " for a colourless zircon.
- " diamond of Colorado " for a transparent smoky quartz.
- " diamond of the Dauphiné " for a hyalin quartz.
- " doublet diamond " for a stone that is in fact a doublet.
- " diamond of Hawaï " for a quartz.
- " Irish diamond " for a quartz.
- " Marmorosch diamond " for a variety of quartz.
- " Matura diamond " for a discoloured zircon.
- " Mexican diamond " for a quartz.
- " diamond of Rennes " for a hyalin quartz.
- " diamond of Nevada " for a discoloured obsidian.
- " black diamond of Nevada " or “Black Diamond” for a hematite or for a carbonado.
- " Occidental diamond " for a quartz.
- " diamond of Pennsylvania " for a pyrite.
- " diamond of the Rhine " for a colourless beryl.
- " diamond of Saxony " for a white topaz.
- " diamond of Tasmania " for a white topaz.
- " diamond of Wight " for a quartz.
- " diamondite " for a white sapphire

See also Gemmological News concerning the diamond.