How To Separate Frequently Encountered Fancy Colored Diamonds From Imitations

- 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 stones may have diagnostic spectrum.

- Microscope: Inclusions may be diagnostic, but look for inclusions that differentiate natural and synthetic, doublet / triplet.

- 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 fancy colored stones, which may resemble one another in appearance and values, are:

Diamond

- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: negative refractive index, dispersion, luster, look at the girdle plane; cleavage, inclusions, weak to strong fluorescence in long wave (may be inert). Diamonds may be treated. Sapphire, synthetic sapphire, spinel, synthetic spinel, zircon, synthetic rutile, synthetic yttrium aluminum garnet (YAG), synthetic gadolium gallium garnet (GGG), synthetic strontium titanate, synthetic cubic zircona (CZ), topaz, quartz, demantoid garnet, sphene, and glass may look like diamond. Standard / analytical techniques may be required to detect treatments / identify the stones.

Synthetic cubic zirconia

- Hardness: 8.5
- Specific gravity: 5.60 – 6.0
- Refractive index: 2.15 – 2.18 (average)
- Optic sign: SR
- Birefringence: -
- Other points: color, negative refractive index, dispersion, luster, orange flash on the pavilion, girdle, inclusions, fluorescence. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the stones.

Synthetic strontium titanate

- Hardness: 5.5
- Specific gravity: 5.13
- Refractive index: 2.41
- Optic sign: SR
- Birefringence: -
- Other points: color, negative refractive index, dispersion, luster, girdle, inclusions, fluorescence, rounded facet edges. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the stones.

Synthetic gadolium gallium garnet (GGG)

- Hardness: 6.5
- Specific gravity: 7.05
- Refractive index: 1.97
- Optic sign: SR
- Birefringence: -
- Other points: color, negative refractive index, dispersion, luster, girdle, color, inclusions, fluorescence (strong orange yellow (LW) and yellow (SW)), rounded facet edges. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the stones.

Synthetic yttrium aluminum garnet (YAG)

- Hardness: 8.5
- Specific gravity: 4.58
- Refractive index: 1.83
- Optic sign: SR
- Birefringence: -
- Other points: color, negative refractive index, dispersion, luster, girdle, inclusions, fluorescence (variable). Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the stones.

Synthetic rutile

- Hardness: 6.5
- Specific gravity: 4.25
- Refractive index: 2.61 – 2.90
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.287
- Other points: color, negative refractive index, strong dispersion, luster, doubling of back facets, inclusions, rounded facet edges. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the stones.

Demantoid garnet

- Hardness: 6.5
- Specific gravity: 3.85
- Refractive index: 1.89
- Optic sign: SR
- Birefringence: -
- Other points: color, negative refractive index reading, dispersion. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the 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, dispersion, negative refractive index, luster, inclusions, doubling of back facets, spectrum. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the stones.

Sphene

- Hardness: 5.5
- Specific gravity: 3.53
- Refractive index: 1.89 – 2.02
- Optic sign: Biaxial positive
- Birefringence: DR; 0.13
- Other points: color, dispersion, negative refractive index, luster, inclusions, doubling of back facets, spectrum. Gem quality stones are relatively clean. Standard / analytical techniques may be required to identify the stones.

Benitoite

- Hardness: 6.5
- Specific gravity: 3.67
- Refractive index: 1.76 – 1.80
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.047
- Other points: Color, inclusions, fluorescence, spectrum, dispersion. Standard / analytical techniques may be required to identify the stones.