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Amethyst
Amethyst is a variety of crystalline quartz (α-quartz), colored in violet. The name comes from the ancient Greek "αμέθυστος" (α - "not" + μέθυστος - "to be drunk").
Chemistry: SiO2;
Crystal system: Trigonal, trigonally trapezohedral symmetry class (point symmetry group);
Color: Purple, violet, reddish violet with pale hues.
Some amethysts have alexandrite effect (transform color hue depending on the light source).
The violet color of amethyst is due to the paramagnetic complex [O- →Fe4+].
Identification properties
| Physical properties | |
|---|---|
| Mohs hardness: | 7 |
| Density: | 2.66±0.01 g/cm3 |
| Cleavage: | none |
| Fracture: | conchoidal |
| Optical properties | |
|---|---|
| Optical character: | anisotropic, uniaxial, positive |
| Refractive Index: | no =1.544, ne =1.553 |
| Birefringence: | 0.009 |
| Pleochroism: | From poor to distinct, purple-reddish-violet hues |
| Dispertion: | 0.013 (BG); |
| Luster: | vitreous |
Inclusions and structural inhomogeneities
Gem basic treatments
| Treatment | Goal |
|---|---|
| Heat treatment (temperature range from 100 to 200°°С) | Removing the smoky and brownish hue, as well as for clarifying dark stones |
Synthetic or Imitation gem materials
Synthetic amethyst is produced by a synthesis methods called hydrothermal growth, based on the principle of temperature gradient.
The most commonly encountered synthetic amethyst is as follows:
- clear quartz treated by irradiation;
- surface-colored quartz;
- quartz treated by "ion impregnation" - very rarely;
- doublet: quartz + glass;
- color glass.
Inclusions and structural inhomogeneities
The accumulation of dye in the cavity on the surface of natural colored quartz. View mode - dark lighting.
The distribution of the dye in the drilling channel and cracks in natural colored quartz. View mode - dark lighting.
The distribution of the dye in the crack in natural colored quartz. View mode - dark lighting.
Gas-liquid inclusion in the seed of synthetic amethyst. View mode - dark lighting.
Fragment of seed in synthetic amethyst. View mode - transmitted diffused light.
Characteristic mineral inclusions in synthetic amethyst of the “chrysanthemum” type, represented by a splice of needle-like crystals (probably wollastonite). View mode - dark lighting
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