ZAFIRINA :

Spanish name ; Prohibited appellation for a blue spinel or a blue chalcedony .

ZAFIRO :

Spanish name for aq sapphire ; used sometimes incorrectly to designate lapis-lazuli

ZARATITE :

Hydrated Carbonate of nickel, sold a long time ago illegally under the appellation of nickel -emerald 

ZEASITE :

Old term . Variety of fire opal .

ZEBEDASSITE :

Synonym for saponite   .

ZEILANITE :

Synonym for ceylonite

ZENITHIT :

Commercial name for fabulite

ZEPHAROWICHITE :

Variety of variscite

ZERMATTITE :

Variety of serpentine from Zermatt ( Switzerland ) ; synonym : Schweitzerite

ZEUXITE :

Variety of ferriferous tourmaline of green colour, originating from Brazil

ZIANITE :

Synonym of cyanite or disthene

ZIMSTEIN :

German synonym for hessonite

ZINC BLENDE :

English name for sphalerite

ZINCITE :

ZnO 

Physical and optical properties :

Colours : red dark to yellowish ; colour red due to des traces de manganese

Transparency : transparent to opaque

Lustre : sub-adamantine

Hardness : 4 to 4.5

Density : 5.4 to 5.7

R.I. : 2.013 – 2.029

Birefringence : 0.016

Cleavage : parfait

System hexagonal

ZINC SPINEL:

Synonym for gahnite .

ZINKSPATH :

German name for smithsonite

ZINNTEIN :

German name for cassiterite

ZIRCOLITE :

Commercial name for an artificial spinel colourless

ZIRCON :

Etym. from the French word : jargon = argot (‘dialect , ‘slang’ ), from its fraudulous use to imitate a diamond

Zr(SiO₄) tetragonal

Physical and optical properties :

There are two distinctly different types:

- the normal or high type, or alpha zircon

-          Colours : honey-yellow, light green, blue and red

        the treated stones are of this type (heated to 800 – 1000 °C) : colourlesss, blue and

        golden yellow

-          Transparency : transparent

-          Lustre : sometimes adamantine

-          Hardness : 7 to 7.5

-          Density : 4.60 to 4.82

-          R.I. : 1.925 – 1.984 (±0.040)

-          Birefringence : 0.059

-          Dispersion : 0.022

-          Dichroism : yellow : very weak : honet-yellow, brownisyellow h

             Blue : distinct : blue, yellow-greyish to colourless

-          Uniaxial positive

-          System tetragonal

- the metamict or low type, or gamma zircon

-          Colours : deep green, green to brownish green

-          Transparency : transparent

-          Lustre : greasy

-          Hardness : 6 to 6.5

-          Density : 3.90 to 4.10

-          R.I. : 1.810 – 1.815 (±0.030)

-          Birefringence : very weak or none : 0.002 to 0.005

-          Uniaxial positive

-          System tetragonal

- there is also an intermediate type, or bèta zircon ;

 these stones become after being treated (heated) colourless stones or left only slightly coloured ; they take on sometimes their original natural colorations after exposure to direct sunlight

-          Colours : generally smoky brown, sometimes reddish brown, yellowish brown or brownish green

-          Transparency : transparent

-          Hardness: 7 to 7.5

-          Density : 4.07 to 4.57

-          R.I. : 1.875 – 1.905 (±0.030)

-          Birefringence : 0.006 to 0.050

-          Dispersion : 0.022

-          Uniaxial positive

-          System tetragonal

ZIRCONITE :

Name given to a brown zircon

ZIRCTONE :

Commercial name given to an artificial corundum of bluish green colour

ZOBLITZITE :

Variety of serpentine

ZOISITE :

Etym.: dedicated to collector Zoïs

Ca₂A1₃(O.OH.SiO₄.Si₂0₇)

Physical and optical properties :

  Colours : green opaque ( anyolithe ), black, apple green, grey-greenish, brown, yellow, grey-

               white, blue ( Tanzanite : colour mostly due to heat-treatment of brown stones), pink

               ( Thulite )

Transparency : transparent to opaque

Lustre : vitreous

Hardness : 6 to 7

Density : 3.25 to 3.37

R.I. : 1.700 – 1.706

Birefringence: 0.006

Biaxial positive

System orthorhombic

ZONITE :

Local name given in Arizona to a jasper with different colours

ZONOCHLORITE :

Variety of amorphous prehnite banded with different green colours

ZOISITE MONOCLINIC :

See clinozoisite