How to identify crystal?
Crystal Introduction
Figure 1 Crystal(citrine)
Quartz is one of the most common rock-forming minerals in the earth’s crust and is also a type of gemstone with a large number of applications in the jewelry industry. monocrystalline quartz is called crystal. Crystal is one of the most common gemstones.
The chemical composition of crystal is silicon dioxide (SiO2), which forms colorless and transparent crystals when pure. When it contains trace elements such as aluminum and iron, the trace elements form different types of color centers after irradiation, producing different colors, such as smoke, purple, yellow, etc.
Crystal Identification
A gemstone that meets all of the following identification characteristics is a crystal.
- Refractive index and birefringence of crystal
The refractive index and birefringence of crystal are measured using a gem refractometer (Figure 2).
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The refractive index (Figure 3) is: 1.544~1.553, and the birefringence is: 0.009.
Figure 2 Gem refractometer |
Figure 3 The refractive index reading |
- Optical characteristics of crystal
The optical characteristics of crystal are mainly detected by a gem polariscope (Figure 4). The authenticity of crystal can be determined by using only a gem polariscope, because only crystal has a “bull’s eye interference figure” (Figure 5).
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The optical characteristics of crystal are: anisotropic body (four bright and four dark under a polariscope), uniaxial crystal, bull’s eye interference figure (Figure 5), and positive optics (measured by a gem refractometer).
Figure 4 Gem polariscope |
Figure 5 uniaxial crystal interference figure |
- Pleochroism of crystal
The pleochroism of crystal is related to body color, it is measured by a dichroscope(Figure 6). The strength of the dichroism of crystal and the color change depend on the color of the crystal itself and the depth of the color. Taking white crystal as an example, the pleochroism is shown in Figure 7, and the pleochroism is relatively weak.
Figure 6 Dichroscope |
Figure 6 dichroism of crystal |
- Crystal Density
The density of crystal is measured by density balance (Figure 8). The density of crystal is relatively stable, which is 2.66g/cm3.
Figure 8 density balance
- Magnify for inspection
Magnified features of the crystal are measured using a gemological microscope (Figure 9).
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Figure 9 gemological microscope
- Natural crystals have abundant internal inclusions. Figures 10 to 19 show the internal features of natural crystals.
Figure 10 Needle-like inclusions
Figure 11 Sheet-like mineral inclusions
Figure 12 Facet edge double image
Figure 13 Gas-liquid inclusion
Figure 14 Mist-like inclusions and fine needle-like inclusions
Figure 15 Green needle-shaped mineral inclusions
Figure 16 Dendritic inclusions
Figure 17 Worm-like inclusions
Figure 18 Oil inclusions
Figure 19 Filamentous inclusions of hair crystal
- Figures 20 and 21 show the magnified observation characteristics of synthetic crystals
Figure 20 Bread-crumb like inclusions
Figure 21 Bread-crumb like inclusions
- Figures 22 and 23 are magnified features of the treated crystal.
Figure 22 Dyed crystal, color distribution along the cracks
Figure 23 Coated crystal