DIAMONTOÏDE :
Synonym of Demantoid.

DIAMONDITE :
Imitation of diamond from the Fashion Craft Company (U.S.A.) with Hardness 9.5
See also :
- Diamondite und Symant, eine Imitation für Diamant mit Härte 9.5, by K. Schlossmacher (ZDG n°30 , 1950, page 9).
- Diamonite et Symant, by K. Schlossmacher (TEC n°176, 1961, page 142).

DIAPHORITE :
Alteration of Rhodonite.

DIASPORE :
Collector’s stone.
AlO(OH)
Physical and optical properties:
- Colours : light brown, yellowish, lilac, pink, pinkish, colourless
- Transparency : Transparent to translucent.
- Lustre vitreous
- Hardness : 6.6 to 7
- S.G. : 3.3 to 3.5
- R.I. : 1.702 - 1.750 (Birefr. : 0.048)
- Biaxial positive
- Crystal system orthorhombic
- Dichroism : white - violet blue - green / reddish brown to reddish violet - grey to green (for stones from Turkey)

Occurrences :
U.S.A., Russia, Uruguay, Turkey.

DIASPRO :
Italian Term designating a kind of Jasper.

DICHROiTE :
Synonym of Iolite

DICKSBERGITE :
Synonym of Rutile.

DILLENBURGITE :
Variety of Chrysocolla.

DIOCROMA :
Variety of Zircon.

DIONYSIAS :
According to Plinius : a black stone, hard and with red spots.

DIOPSIDE :
Belongs to the group of the pyroxenes.
Silicate of calcium and magnesium.
CaMg(SiO₃)₂
Physical and optical properties:
- Colours : light green to dark green, bottle green, yellow and colourless (rare), vivid green  chromiferous, dark green to black, blue-violet
- transparency : Translucent to opaque (violane)
- lustre : vitreous lustre (violane : greasy aspect )
- Hardness : 5.5 to 6 (for violane).
- S.G. : 3.2 to 3.31 (violane 3.23).
- R.I. : 1.664 - 1.765 (Birefr. : +0.030 ; violane : 0.009).
- Biaxial positive.
- Crystal system monoclinic.
- Spectrum : specific absorption : 3 bands in the blue or chrome spectrum for vivid green diopside.
- Cleavage perfect.
- Fracture conchoidal.
- Pleochroism weak yellow green, grass green , olive green.
- Fluorescence strong dark violet.
Optical particularities :
Sometimes, diopside can be chatoyant or even asteriated. The asteriated stone is very dark green, almost black ad slightly magnetic.
The star shows four branches ad is caused by the presence of fine allongated lamellae of magneto-ilmenite intersecting at 73°.
Occurrences :
Product of regional or contact metamorphism. Sometimes accompanying calcium-garnet, epidote,  spinel or scapolite.
It is a common mineral in kimberlites.
Kimberley (chrome-diopside), Myanmar (cat’s eye chrome-diopside ), Italy, Austria, Sri Lanka, Brazil, Scandinavia, Canada, U.S.A., Russia.
See also :
- Diopside Katzenauge (ZDG n°54 , 1965, page 36).
- Sterndiopside und Sternenstatite, by W. F. Eppler (ZDG n°62 , 1967, page 55).
- Nature des inclusions du diopside black étoilé de l'India, by C. Mario, P. Picot & H. J. Schubnel (AFG n°12, page 11).
- A propos de la " Sibérite ", by J.P. Poirot (AFG n°26, page 5).

DIOPSIDE-JADEITE :
Term employed for a pyroxene intermediate between Jadeite and Diopside, and designated in central America under the name of Sado-jadeite.

DIOPTASE :
Collector’s stone
Hydrosilicate of copper.
Cu₆[Si₆O₁₈]. 6H₂
Physical and optical properties:
- Colours : emerald green, bluish green, grey green, blackish green
- Transparency : Translucent to transparent
- lustre : vitreous
- Hardness : 5
- S.G. : 3.30
- R.I. : 1.644 (+0.012) - 1.697 (+0.012) (Birefr. : +0.051 to +0.054)
- Uniaxial positive
- Crystal system : trigonal  according to Lapadu and others (prismatic crystals and generally rhomboedrically terminated); hexagonal according to Webster
- Pleochroism rather weak : deep green / luminescent green.
- Spectrum : absorption bands in the blue and the violet and a large part of the yellow-green.
- Appears black under Chelsea filter.
- Fracture irregular.
- Cleavage perfect following rhombohedron.
Occurrences :
Turkestan, Russia, Congo, Namibia, Chili, Arizona.
Confusions :
Emerald (S.G. 2.7 ; R.I. 1.57 ; reddish or grey under Chelsea filter)

DIOPTASITE :
Synonym of Dioptase.

DIPYRE :
Or Dipyrite.
Name given to a Scapolite.
See also :
- Scapolite, by Rüdiger Perizonius (ZDG n°57of 1966, page 41)

DIRIGEM :
Commercial name for a synthetic spinel of green colour.

DISTHENE :
Synonym for Kyanite or Cyanite.
 
DISTRENE :
Plastic material used to imitate amber.
Physical and optical properties:
- Colours : idem amber.
- Hardness :
- S.G. : 1.05 (according to Anderson)
- R.I. : 1.58

DITROITE :
Or Ditroyte.
Synonym for Sodalite.
Name given by certain German authors.

DJEVALITE :
Variety of synthetic Cubic Zirconium (CZ).
Artificial product imitating Diamond.
ZrO₂ + 10 – 17 % CaO
Physical and optical properties:
- Colours : colourless to light brownish
- Transparency : Transparent
- Hardness : 8 to 8.5
- S.G. : 5.6 to 5.7
- R.I. : 2.177 (±0.005)
- Crystal system : cubic
- under S.W.U.V. : weak brownish

DOLIANITE :
Variety of Apophyllite.

DOLOMITE :
Etym. : named after the French mineralogist and geologist D. de Dolomieu (1750-1801)
Collector’s stone
CaMg(CO₃)₂  
Physical and optical properties:
- Colours : colourless or pastel colours, grey, greenish, brown.
- Transparency : transparent to translucent
- Lustre : vitreous
- Hardness : 3.5 to 4.5
- S.G. : 2.85 to 2.95
- R.I. : 1.500 - 1.680 (birefr. : - 0.180)
- Uniaxial negative
- Crystal system : trigonal

DOMEYKITE :
Etym. : named after the Chilean mineralogist, I. Domeyk (1802-1889).
Collector’s stone
Arsenide of Cu
Cu₃As
Physical and optical properties:
- Colours : white the colour of tin to metallic grey (sometimes dark brown).
- Transparency : opaque
- Lustre : metallic
- Hardness : 3.0 to 3.5
- S.G. : 7.2 to 8.1
Occurrences :
Michigan, USA

DOPPELSPATH :
Or Doppelstein. German.
Synonym for Iceland spar.  Name referring to its strong birefringence.

DOUBLET :
Stone composed of two parts : two gemstones, or one gem and one glass part or two glasses, serving to make with two small stones one bigger stone or to imitate a natural gemstone.
(Example : upper part made of garnet for its lustre and hardness, and the lower part made out of  a coloured glass in the colour of the gem it is imitating).

DRAGEE DE CARLSBAD :
French. Small calcareous concretions the size of a pea, also called " Perles des Cavernes " (pearls of the caves).

DRAGOMITE :
Or D'Ragomite or Dragonite.
Rock crystal of Marmarosch, Galicia.

DRAGONITE :
Mythical stone, according to Plinius found in the head of a dragon, probably a quartz (pebble) of rounded form.

DRAVITE :
Variety of magnesium-Tourmaline, of yellow-green to dark brown colour that can become colourless by heating.

DRIMYLLUS :
Or Stone of Drimyllus.
According to Plutarchus, a stone similar to a sardonyx and found near the Euphrate, at Mount Drimyllus.

DUFRENITE :
Hydrated phosphate found in massive or fibrous concretions, of green colour passing, due to alteration, into yellow and brown.
Fe++Fe+++₄(PO₄)₃(OH)₅·2(H₂O)
Physical and optical properties:
- Colours : Brown, Greenish brown, Green black, Dark green, Olive green.
- Transparency : opaque
- Lustre : silky
- Hardness : 3.5 to 4
- S.G. : 3.2 to 3.4
- R.I. : a=1.82-1.842, b=1.83-1.85, g=1.875-1.925 (birefr. : 0.055-0.083)
- Biaxial (+/-)
- Crystal system : monoclinic

DUMORTIERITE :
Etym. : named after the French paleontologist, M. E. Dumortier (1803-1873).
Al₇(BO₃)(SiO₄)₃(O,OH)₃
Physical and optical properties:
- Colours : cobalt blue, blue-violet, pink, violet
- Transparency : Translucent to opaque
- Lustre : vitreous
- Hardness : 7
- S.G. : 3.26 to 3.41
- R.I. : 1.675 - 1.692 ( Birefr. : - 0.017 ; brownish red : - 0.037)
- Biaxial negative
- Crystal system : orthorhombic
- Dichroism : very strong : blue / violet red / colourless or blue / yellow / colourless, for the red-brown : black / deep red brown / brown.
- Good cleavage following the prism.
Occurrences :
Madagascar, Brazil, Canada, U.S.A., Sri Lanka, France, Norway.

DURANGITE :
Collector’s stone
NaAl[F|AsO₄] 
Physical and optical properties:
- Colours : light yellow, dark green, red-orange, red.
- Transparency : transparent to translucent
- Lustre : vitreous
- Hardness : 5
- S.G. : 3.97 to 4.07
- R.I. : 1.662 - 1.712 (Birefr. : - 0.050)
- Biaxial negative.
- Dichroism : colourless / very pale yellow / yellow-orangy
Occurrences :
Durango, Mexico

DUPA XAGO :
Term employed by the Pomo indians of California for designating an obsidian harder than the Bati Xaga.

DYSLUITE :
Variety of brownish Gahnite containing zinc, manganese and iron.

DYSSYNTRIBITE :
Variety of .