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Zircon
Zircon is a mineral which chemical name is zirconium silicate. It is possible that this particular mineral called "hyacinthus" is mentioned in the "Natural History of Fossil Tel" by Guy Pliny the Elder. However, V.Severgin expresses doubts that this term was understood to be zircon, but not another mineral (Severgin points to cordierite) or a group of minerals with the similar color in his comments on the Russian translation of 1810 . The modern name of the mineral was given by the German naturalist Abraham Gottlob Werner (p. 1749 - p. 1817) in his work "On the External Signs of Fossil Bodies" (Von den äußerlichen Kennzeichen der Fossilien) in 1774. Zircon, together with hyacinth, are given as two varieties in the "order of zircon" (Ordnung des Zirkons) in the book "Guide to Mineralogy for Lectures Developed by Christian Frederick Ludwig" in 1803. The name zircon (zirkon) is derived from the German, which is the Persian adaption of the yellow-orange variety "jargon" - "زرگون" ("zergun" - golden, "zar" - gold, "hun" – color).
Chemistry: ZrSiO4;
Crystal system: Tetragonal, ditetragonal-dipyramidal crystal class (point symmetry group);
Color: Zircon occurs in an array of colors. Its wide and varied palette of colorless, golden yellow, orange, red, green, blue, purple, brown, and black; but most often in nature are widespread yellow-orange with a red hue of different intensity.
There are jewelry color varieties as follows:
- colorless zircon;
- hyacinth - reddish brown, to purplish red;
- jargon - yellow, orange, with brown hues;
- starlite - blue, blue, with green hue.
The color of the hyacinth is due to the presence of a structural admixture of Nb4+ (changing the charge of Nb5+), Y3+ and other rare earth elements according to the number of researchers.
Окраска jargon is due to the presence of a hole-type defect in the crystal lattice. A defect is formed as a result of the presence of a heterovalent isomorphism of the impurity of the Fe3+ ion replacing Si4+ in combination with the irradiation.
The color of the starlite is not clear yet.
Identification properties
| Physical properties | |
|---|---|
| Mohs hardness: | 6.5-8 |
| Density: | 3.93 – 4.73 g/cm3 |
| Cleavage: | very poor |
| Fracture: | uneven, conchoidal |
| Optical properties | |
|---|---|
| Optical character: | anisotropic, uniaxial, positive |
| Refractive Index: | 1.810 – 2.024 |
| Birefringence: | 0.002 – 0.059 |
| Pleochroism: | weak |
| Dispertion: | 0.039 (BG) |
| Luster: | diamond, glassy, vitreous |
Inclusions and structural inhomogeneities
Gem basic treatments
| Treatment | Goal |
|---|---|
| Heat treatment | Altering or improving the apparent color of gem material |
| Irradiation treatment | Altering or improving the apparent color of gem material |
| Surface coating by applying a various coloring agent | Altering or improving the apparent color of gem material |
Synthetic or Imitation gem materials
There is no data on the production of synthetic zircon for the jewelry.
As a rule, imitation zircon is not produced, but sometimes there are attempts to give phianites for zircon and other synthetic materials similar in composition and crystal structure to phianite.
