- Visual observation: (10x lens) Look for color, luster, cut, doublet/triplet junctions, if any.
- Determine optic character: Single refractive (SR) / Double refractive (DR) / Anomalous Double refractive (ADR) / Aggregate (AGG).
- Spectrum: Many yellow stones may have diagnostic spectrum.
- Microscope: Inclusions may be diagnostic, but look for inclusions that differentiate natural and synthetic, doublet / triplet.
- Dichroscope: Different cutting orientations of natural and synthetic corundum may be revealed by dichroscope.
- Fluorescence: Look under shortwave and longwave for diagnostic colors.
- Immersion cell: Use immersion cell and high refractive index liquid to separate doublets/triplets.
- Refractometer: Confirm spectroscope reading with refractometer.
The yellow stones, which may resemble one another in appearance and values, are:
Quartz, Citrine
- Hardness: 7
- Specific gravity: 2.65
- Refractive index: 1.54 – 1.55
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.009
- Other points: Color, inclusions. Citrine may be treated. Gem quality stones are relatively clean. Common look-alikes are yellow beryl, yellow labradorite, scapolite, and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Synthetic quartz , citrine
- Hardness: 7
- Specific gravity: 2.65
- Refractive index: 1.54 – 1.55
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.009
- Other points: Color, inclusions, twinning pattern. Synthetic citrine is produced by the hydrothermal process. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify stones.
Feldspar, Orthoclase
- Hardness: 6
- Specific gravity: 2.56
- Refractive index: 1.52 – 1.53
- Optic sign: Biaxial negative
- Birefringence: DR; 0.006
- Other points: Color, inclusions, cleavage. Gem quality stones are relatively clean. Common look-alikes are yellow beryl, citrine, scapolite, and glass. Standard / analytical techniques may be required to identify stones.
Feldspar, Labradorite
- Hardness: 6
- Specific gravity: 2.70 (average)
- Refractive index: 1.56 – 1.57
- Optic sign: Biaxial positive
- Birefringence: DR; 0.009
- Other points: Color, inclusions, cleavage. Gem quality stones are relatively clean. Common look-alikes are yellow beryl, citrine, scapolite, and glass. Standard / analytical techniques may be required to identify stones.
Beryl
- Hardness: 7.75
- Specific gravity: 2.70 – 2.90
- Refractive index: 1.56 – 1.59
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.005/9
- Other points: Color, inclusions. Gem quality stones are relatively clean. Yellow beryl may treated. Common look-alikes are yellow labradorite, citrine, scapolite, and glass. Standard / analytical techniques may be required to identify stones.
Scapolite
- Hardness: 6
- Specific gravity: 2.50-2.70
- Refractive index: 1.54 – 1.58
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.009 - 026
- Other points: Color, inclusions, fluorescence. Gem quality stones are relatively clean. Common look-alikes are yellow labradorite, citrine, yellow beryl, and glass. Standard / analytical techniques may be required to identify stones.
Apatite
- Hardness: 5
- Specific gravity: 3.18
- Refractive index: 1.63 – 1.64
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.002 – 0.004
- Other points: Color, inclusions, spectrum. Apatite may be treated. Gem quality stones are relatively clean. Common imitations include chrysoberyl, sapphire, tourmaline, danburite, peridot, topaz and glass. Standard / analytical techniques may be required to identify stones.
Danburite
- Hardness: 7
- Specific gravity: 3.00
- Refractive index: 1.63 – 1.64
- Optic sign: Biaxial negative
- Birefringence: DR; 0.006
- Other points: Color, inclusions, spectrum. Gem quality stones are relatively clean. Common imitations include chrysoberyl, sapphire, tourmaline, apatite, peridot, topaz and glass. Standard / analytical techniques may be required to identify stones.
Topaz
- Hardness: 8
- Specific gravity: 3.53
- Refractive index: 1.63 – 1.64
- Optic sign: Biaxial positive
- Birefringence: DR; 0.008
- Other points: Color, inclusions, cleavage. Topaz may be treated. Gem quality stones are relatively clean. Common imitations include chrysoberyl, sapphire, tourmaline, apatite, peridot, danburite and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Tourmaline
- Hardness: 7
- Specific gravity: 3.05
- Refractive index: 1.62 – 1.64
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.018
- Other points: Color, inclusions, doubling of back facets, pleochroism. Tourmaline may be treated. Gem quality stones are relatively clean. Common imitations include chrysoberyl, sapphire, topaz, apatite, peridot, danburite and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Idocrase
- Hardness: 6.5
- Specific gravity: 3.35
- Refractive index: 1.70 – 1.73
- Optic sign: Uniaxial negative / positive
- Birefringence: DR; 0.005
- Other points: Color, spectrum. Common imitations include chrysoberyl, sapphire, topaz, apatite, peridot, danburite, tourmaline, and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Grossular garnet
- Hardness: 7.25
- Specific gravity: 3.60 – 3.70
- Refractive index: 1.74 – 1.75
- Optic sign: SR
- Birefringence: -
- Other points: Color, inclusions. Gem quality stones are relatively clean. Common imitations include chrysoberyl, sapphire, topaz, apatite, peridot, danburite, tourmaline, and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Chrysoberyl
- Hardness: 8.5
- Specific gravity: 3.72
- Refractive index: 1.74 – 1.75
- Optic sign: Biaxial positive
- Birefringence: DR; 0.009
- Other points: Color, inclusions, spectrum. Chrysoberyl may be treated. Gem quality stones are relatively clean. Common imitations include idocrase, hessonite garnet, sapphire, topaz, apatite, peridot, danburite, tourmaline, and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Sapphire
- Hardness: 9
- Specific gravity: 4
- Refractive index: 1.76 – 1.77
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Color, inclusions, spectrum. Yellow sapphire may be treated. Gem quality stones are relatively clean. Common imitations include chrysoberyl, idocrase, hessonite garnet, topaz, apatite, peridot, danburite, tourmaline, and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Andradite garnet (yellow demantoid)
- Hardness: 6.5
- Specific gravity: 3.85
- Refractive index: 1.89
- Optic sign: SR
- Birefringence: -
- Other points: Color, inclusions, negative refractive index reading, spectrum, dispersion, luster. Common imitations include chrysoberyl, idocrase, sapphire, topaz, apatite, peridot, danburite, tourmaline, zircon, sphene, and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Zircon
- Hardness: 7.5
- Specific gravity: 4.69
- Refractive index: 1.93 – 1.99
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.059
- Other points: Color, inclusions, doubling of back facets, spectrum, luster. Zircon may be treated. Gem quality stones are relatively clean. Common imitations include chrysoberyl, idocrase, sapphire, topaz, apatite, peridot, danburite, tourmaline, demantoid garnet, sphene and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Sphene
- Hardness: 5.5
- Specific gravity: 3.53
- Refractive index: 1.89 – 2.02
- Optic sign: Biaxial positive
- Birefringence: DR; 0.051
- Other points: Color, negative refractive index reading, dispersion, doubling of back facets, spectrum. Common imitations include chrysoberyl, idocrase, sapphire, topaz, apatite, peridot, danburite, tourmaline, zircon, demantoid garnet and glass. Standard / analytical techniques may be required to detect treatments / identify stones.
Synthetic cubic zirconia
- Hardness: 8.5
- Specific gravity: 5.65+
- Refractive index: 2.15+
- Optic sign: SR
- Birefringence: -
- Other points: Color, inclusions, negative refractive index, luster, dispersion, orange flash on the pavilion. Most gem quality stones are relatively clean. High dispersion will easily identify the stone. Standard / analytical techniques may be required to identify stones.
Diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Color, negative refractive index reading, dispersion, spectrum, inclusions. Yellow diamonds may be treated. Gem quality stones are relatively clean. Common imitations are synthetic cubic zirconia, synthetic moissanite, synthetic strontium titanate, GGG and glass. Analytical / standard techniques may be required to detect treatments / identify the stones.
Synthetic diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Color, negative refractive index reading, dispersion, spectrum, inclusions. Synthetic yellow diamonds are produced by high pressure high temperature method. Gem quality stones are relatively clean. Analytical / standard techniques may be required to identify the stones.
Glass
- Hardness: 5.5
- Specific gravity: 3.70
- Refractive index: 1.60 – 1.66
- Optic sign: SR
- Birefringence: -
- Other points: Color, soft, inclusions (gas bubbles, swirls), luster, spectrum.
Assembled Stones
Doublets / Triplets
Corundum composites (natural crown/synthetic base)
Refractive index: 1.76 – 1.77
Birefringence: DR; 0.008
Other points: Immersion (Look for differences in color and luster between the sections)
Garnet topped doublet (glass)
- Refractive index: 1.76 +
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Look for differences in color and luster between the sections, gas bubbles)
No comments:
Post a Comment