The appearance of asterism can be produced on almost any transparent cabochon by cutting hundreds of fine grooves into its base. The grooves are usually cut in three directions with a diamond tool, and a mirror or a mirror-like coating is attached to the back. This creates a 6-rayed star of reasonable intensity. The mirror on the back of the stone and the appearance of the star is quite easy to identify. Usually synthetic gemstones are used in this imitation.
The most effective imitation star stone is made by placing a hollow cabochon of synthetic corundum over a piece of asteriated natural corundum, and then closing the back with a third piece. Once assembled and set in a piece of jewelry the girdle plane can be hidden by the setting. Sometimes a slice of black star corundum is glued to the back of the cabochon of synthetic corundum. The assembled stones can easily identified by their separation planes.
Another good imitation star stone is made up of a white opaque glass which is pressed into a mold to form cabochon with six raised ridges on the crown. The ridged cabochon is then coated with a thin layer of deep blue glaze which barely covers the ridges. The finished stone has a very similar appearance to a natural star sapphire with the star on or just below the surface. The stones are easy to identify because the stars does not move or roll across the surface when the stone is turned. Physical constants are typical of glass, not corundum.
Star diopside and star enstatite are two less-known inexpensive stones, which are often confused with one another. Both may display four rayed stars which meet at almost 90º. The reason for confusion is that they are frequently mixed into the same lots and sold as black stars. Star diopside usually display very sharp star, while enstatite may show weaker more diffused star and a unique bronzy sheen. Enstatite may also display eight rayed star.
Wednesday, January 17, 2007
Tuesday, January 16, 2007
How To Separate Frequently Encountered Red Stones
- 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 red 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 red stones, which may resemble one another in appearance and values, are:
Red Beryl
- Hardness: 7.5
- Specific gravity: 2.70 (average)
- Refractive index: 1.57 – 1.58
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.006
- Other points: Inclusions, color. There are many treated stones in the gem market. Analytical techniques may be required to detect treatments.
Tourmaline
- Hardness: 7
- Specific gravity: 3.03
- Refractive index: 1.62 – 1.64
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.018
- Other points: Inclusions, color, pleochroism. There are many treated stones in the gem market. Many gem quality tourmalines are relatively clean. Analytical techniques may be required to detect treatments.
Topaz
- Hardness: 8
- Specific gravity: 3.53
- Refractive index: 1.63 – 1.64
- Optic sign: Biaxial positive
- Birefringence: DR; 0.008
- Other points: Inclusions, color (pink stones may be confused for pink sapphires). There are many treated stones in the market. Most gem quality stones are relatively clean. Analytical techniques may be required to detect treatments.
Spinel
- Hardness: 8
- Specific gravity: 3.60
- Refractive index: 1.718
- Optic sign: SR
- Birefringence: -
- Other points: Inclusions, color, spectrum.
Garnet (pyrope)
- Hardness: 7.5
- Specific gravity: 3.78 (average)
- Refractive index: 1.75 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Garnet (almandine)
- Hardness: 7.5
- Specific gravity: 4.10 (average)
- Refractive index: 1.78 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to separate natural vs synthetic). There are many treated stones in the gem market. Analytical techniques may be required to detect treatments.
Synthetic Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to differentiate flux and hydrothermal). Gem quality stones are relatively clean.
Synthetic red cubic zirconia
- Hardness: 8.5
- Specific gravity: 5.65 +
- Refractive index: 2.15 +
- Optic sign: SR
- Birefringence: -
- Other points: negative refractive index, luster, color, orange flash on the pavilion, dispersion. Gem quality stones are relatively clean.
Red Zircon
- Hardness: 7.5
- Specific gravity: 4.69
- Refractive index: 1.93 – 1.99
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.059
- Other points: Inclusions, color, spectrum, doubling of the back facets, dispersion, luster, negative refractive index reading. There are many treated stones in the gem market. Analytical techniques may be required to detect treatments.
Red Diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Rare, negative refractive index reading, inclusions, luster, spectrum, dispersion. There are many treated stones in the market. Most treated diamonds are relatively clean. Analytical techniques may be required to detect treatments.
Synthetic red diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Negative refractive index reading, color, inclusions, luster, spectrum, fluorescence. Synthetic diamonds are produced by the high pressure high temperature method. Gem quality stones are relatively clean. Analytical 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/ADR
- Birefringence: -
- Other points: Soft, inclusions (gas bubbles), color.
Assembled Stones
Doublets / Triplets
Corundum (natural crown / synthetic base)
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).
Synthetic spinel soude (spinel / spinel)
- Refractive index: 1.728
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Look for differences in color and luster between the sections, gas bubbles).
- Determine optic character: Single refractive (SR) / Double refractive (DR) / Anomalous Double refractive (ADR) / Aggregate (AGG).
- Spectrum: Many red 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 red stones, which may resemble one another in appearance and values, are:
Red Beryl
- Hardness: 7.5
- Specific gravity: 2.70 (average)
- Refractive index: 1.57 – 1.58
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.006
- Other points: Inclusions, color. There are many treated stones in the gem market. Analytical techniques may be required to detect treatments.
Tourmaline
- Hardness: 7
- Specific gravity: 3.03
- Refractive index: 1.62 – 1.64
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.018
- Other points: Inclusions, color, pleochroism. There are many treated stones in the gem market. Many gem quality tourmalines are relatively clean. Analytical techniques may be required to detect treatments.
Topaz
- Hardness: 8
- Specific gravity: 3.53
- Refractive index: 1.63 – 1.64
- Optic sign: Biaxial positive
- Birefringence: DR; 0.008
- Other points: Inclusions, color (pink stones may be confused for pink sapphires). There are many treated stones in the market. Most gem quality stones are relatively clean. Analytical techniques may be required to detect treatments.
Spinel
- Hardness: 8
- Specific gravity: 3.60
- Refractive index: 1.718
- Optic sign: SR
- Birefringence: -
- Other points: Inclusions, color, spectrum.
Garnet (pyrope)
- Hardness: 7.5
- Specific gravity: 3.78 (average)
- Refractive index: 1.75 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Garnet (almandine)
- Hardness: 7.5
- Specific gravity: 4.10 (average)
- Refractive index: 1.78 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to separate natural vs synthetic). There are many treated stones in the gem market. Analytical techniques may be required to detect treatments.
Synthetic Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to differentiate flux and hydrothermal). Gem quality stones are relatively clean.
Synthetic red cubic zirconia
- Hardness: 8.5
- Specific gravity: 5.65 +
- Refractive index: 2.15 +
- Optic sign: SR
- Birefringence: -
- Other points: negative refractive index, luster, color, orange flash on the pavilion, dispersion. Gem quality stones are relatively clean.
Red Zircon
- Hardness: 7.5
- Specific gravity: 4.69
- Refractive index: 1.93 – 1.99
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.059
- Other points: Inclusions, color, spectrum, doubling of the back facets, dispersion, luster, negative refractive index reading. There are many treated stones in the gem market. Analytical techniques may be required to detect treatments.
Red Diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Rare, negative refractive index reading, inclusions, luster, spectrum, dispersion. There are many treated stones in the market. Most treated diamonds are relatively clean. Analytical techniques may be required to detect treatments.
Synthetic red diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Negative refractive index reading, color, inclusions, luster, spectrum, fluorescence. Synthetic diamonds are produced by the high pressure high temperature method. Gem quality stones are relatively clean. Analytical 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/ADR
- Birefringence: -
- Other points: Soft, inclusions (gas bubbles), color.
Assembled Stones
Doublets / Triplets
Corundum (natural crown / synthetic base)
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).
Synthetic spinel soude (spinel / spinel)
- Refractive index: 1.728
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Look for differences in color and luster between the sections, gas bubbles).
How To Observe Fluorescence Under Ultraviolet Light
- Make observations in a darkened environment. Allow a few moments for your eyes to adjust to the darkness in order to be able to detect weak fluorescence.
- Place the stone (s) on a non-reflective background directly under the light source. In order to be sure that the color noted is actually a fluorescent effect, and not a reflection of the Ultraviolet light source from the facets of the stone, always position the stone in several directions.
- Look for a dull powdery color on the surface of the stone (ignore color due to the surface reflection of visible light and from light leaking into the test unit). Record, in both long and short wave ultraviolet light, the reaction of the stone as Inert, Weak, or Strong fluorescence and note the color.
Note: If the stone fluoresces strongly, look for phosphorescence (after-glow).
- Observe the crown, pavilion and girdle of the stone, as it may be a doublet or a triplet.
- Place the stone (s) on a non-reflective background directly under the light source. In order to be sure that the color noted is actually a fluorescent effect, and not a reflection of the Ultraviolet light source from the facets of the stone, always position the stone in several directions.
- Look for a dull powdery color on the surface of the stone (ignore color due to the surface reflection of visible light and from light leaking into the test unit). Record, in both long and short wave ultraviolet light, the reaction of the stone as Inert, Weak, or Strong fluorescence and note the color.
Note: If the stone fluoresces strongly, look for phosphorescence (after-glow).
- Observe the crown, pavilion and girdle of the stone, as it may be a doublet or a triplet.
Trapiche Emerald
Trapiche emeralds consist of emerald crystals which contain inclusions of a mixture of albite feldspar and beryl. These inclusions radiate out from a hexagonal core to form a six spoke pattern.
Trapiche emeralds are unique to the Colombian deposits, but similar crystals have been found in Brazil and elsewhere. Trapiche is the Spanish word for cog wheels once used to crush sugarcane. If certain types of trapiche emeralds are cut as cabochons with the base perpendicular to the crystallographic axis of the crystal, a hexagonal chatoyancy may be seen. It is due to fibrous inclusions contained in each of the six spokes that radiate outward from the core.
Trapiche emeralds are unique to the Colombian deposits, but similar crystals have been found in Brazil and elsewhere. Trapiche is the Spanish word for cog wheels once used to crush sugarcane. If certain types of trapiche emeralds are cut as cabochons with the base perpendicular to the crystallographic axis of the crystal, a hexagonal chatoyancy may be seen. It is due to fibrous inclusions contained in each of the six spokes that radiate outward from the core.
Natural Diamonds Face Competition From Synthetic
Times News Network writes:
While the gems and jewellery industry is preparing itself to take on the Chinese dragon, the problem of synthetic diamonds making steady in-roads lurks beneath the shiny surface of the industry.
“India is a price sensitive market and synthetic diamonds could give competition to natural diamonds over the next decade,” said Ronald Lorie, CEO of International Gemological Institute (IGI).
Synthetic or cultured diamonds are laboratory-created diamonds that have the same chemical, optical and physical characteristics as mined diamonds. The two are literally indistinguishable to the naked eyes.
The IGI’s Mumbai Gemological laboratory receive close to three to four synthetic diamonds of yellowish orange colour every week, which are easily identifiable. But it is not the case with white synthetic diamonds, which look very similar to original diamonds, admits Mr Lorie.
Even the recently published KPMG report on the industry speaks broadly about the emergence of synthetic diamonds as a commercially viable alternative posing a new challenge for the world’s diamond industry. There is a dual threat to the natural diamond industry — threat of substitution and deception impacting consumer confidence and the threat of changing consumer preference, said the report.
The KPMG has estimated the current value of synthetic at wholesale to be close to $50 million and expects the market to grow at a CAGR of 45% over the next 10 years. Giving the current situation the sale of synthetic diamonds jewellery is likely to cross $2 billion by 2015 at wholesale against the sale of natural diamond jewellery sales of $6 billion at the retail level.
With the view to inform and protect the consumers and the industry, the IGI has started grading the synthetic diamonds from January 1, 2007. IGI has been laser inscribing synthetic diamonds it grades this way with the words ‘laboratory-grown,’ said Mr Lorie.
Chandrakant Sanghvi, regional chairman of GJEPC said: “There is no threat to the industry at this moment.” But synthetic diamonds could replace the natural diamonds in jewellery due to its cheap value.”
Chuni Gajera owner of Laxmi Diamond said: “Synthetic diamond can give a stiff competition to natural diamonds. But synthetics are not being sold as real. Synthetics could gain momentum in the sale of jewellery.
More info @ http://economictimes.indiatimes.com/Markets/Commodities/Natural_diamonds_face_competition_from_synthetics_/articleshow/1144422.cms
While the gems and jewellery industry is preparing itself to take on the Chinese dragon, the problem of synthetic diamonds making steady in-roads lurks beneath the shiny surface of the industry.
“India is a price sensitive market and synthetic diamonds could give competition to natural diamonds over the next decade,” said Ronald Lorie, CEO of International Gemological Institute (IGI).
Synthetic or cultured diamonds are laboratory-created diamonds that have the same chemical, optical and physical characteristics as mined diamonds. The two are literally indistinguishable to the naked eyes.
The IGI’s Mumbai Gemological laboratory receive close to three to four synthetic diamonds of yellowish orange colour every week, which are easily identifiable. But it is not the case with white synthetic diamonds, which look very similar to original diamonds, admits Mr Lorie.
Even the recently published KPMG report on the industry speaks broadly about the emergence of synthetic diamonds as a commercially viable alternative posing a new challenge for the world’s diamond industry. There is a dual threat to the natural diamond industry — threat of substitution and deception impacting consumer confidence and the threat of changing consumer preference, said the report.
The KPMG has estimated the current value of synthetic at wholesale to be close to $50 million and expects the market to grow at a CAGR of 45% over the next 10 years. Giving the current situation the sale of synthetic diamonds jewellery is likely to cross $2 billion by 2015 at wholesale against the sale of natural diamond jewellery sales of $6 billion at the retail level.
With the view to inform and protect the consumers and the industry, the IGI has started grading the synthetic diamonds from January 1, 2007. IGI has been laser inscribing synthetic diamonds it grades this way with the words ‘laboratory-grown,’ said Mr Lorie.
Chandrakant Sanghvi, regional chairman of GJEPC said: “There is no threat to the industry at this moment.” But synthetic diamonds could replace the natural diamonds in jewellery due to its cheap value.”
Chuni Gajera owner of Laxmi Diamond said: “Synthetic diamond can give a stiff competition to natural diamonds. But synthetics are not being sold as real. Synthetics could gain momentum in the sale of jewellery.
More info @ http://economictimes.indiatimes.com/Markets/Commodities/Natural_diamonds_face_competition_from_synthetics_/articleshow/1144422.cms
How To Separate Frequently Encountered Red Stones
- 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 red 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 red stones, which may resemble one another in appearance and values, are:
Red Beryl
- Hardness: 7.5
- Specific gravity: 2.70 (average)
- Refractive index: 1.57 – 1.58
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.006
- Other points: Inclusions, color.
Tourmaline
- Hardness: 7
- Specific gravity: 3.03
- Refractive index: 1.62 – 1.64
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.018
- Other points: Inclusions, color, pleochroism. There are many treated tourmalines in the gem market. Many
gem quality tourmalines are relatively clean. Analytical techniques may be required to detect treatments.
Topaz
- Hardness: 8
- Specific gravity: 3.53
- Refractive index: 1.63 – 1.64
- Optic sign: Biaxial positive
- Birefringence: DR; 0.008
- Other points: Inclusions, color (pink stones may be confused for pink sapphires). There are many treated
topaz in the market. Most gem quality stones are relatively clean. Analytical techniques may be required
to detect treatments.
Spinel
- Hardness: 8
- Specific gravity: 3.60
- Refractive index: 1.718
- Optic sign: SR
- Birefringence: -
- Other points: Inclusions, color, spectrum.
Garnet (pyrope)
- Hardness: 7.5
- Specific gravity: 3.78 (average)
- Refractive index: 1.75 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Garnet (almandine)
- Hardness: 7.5
- Specific gravity: 4.10 (average)
- Refractive index: 1.78 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to separate natural vs synthetic).
Synthetic Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to differentiate flux and hydrothermal).
Synthetic red cubic zirconia
- Hardness: 8.5
- Specific gravity: 5.65 +
- Refractive index: 2.15 +
- Optic sign: SR
- Birefringence: -
- Other points: negative refractive index, luster, color, orange flash on the pavilion, dispersion.
Red Zircon
- Hardness: 7.5
- Specific gravity: 4.69
- Refractive index: 1.93 – 1.99
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.059
- Other points: Inclusions, color, spectrum, doubling of the back facets, dispersion, luster, negative refractive
index reading.
Red Diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Rare, negative refractive index reading, inclusions, luster, spectrum, dispersion. There are
many treated diamonds in the market. Most treated diamonds are relatively clean. Analytical techniques
may be required to detect treatments.
Synthetic red diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Negative refractive index reading, color, inclusions, luster, spectrum, fluorescence. Synthetic
diamonds are produced by the high pressure high temperature method. Gem quality stones are relatively
clean. Analytical 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/ADR
- Birefringence: -
- Other points: Soft, inclusions (gas bubbles), color.
Assembled Stones
Doublets / Triplets
Corundum (natural crown / synthetic base)
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).
Synthetic spinel soude (spinel / spinel)
- Refractive index: 1.728
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Look for differences in color and luster between the sections, gas bubbles).
- Determine optic character: Single refractive (SR) / Double refractive (DR) / Anomalous Double
refractive (ADR) / Aggregate (AGG).
- Spectrum: Many red 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 red stones, which may resemble one another in appearance and values, are:
Red Beryl
- Hardness: 7.5
- Specific gravity: 2.70 (average)
- Refractive index: 1.57 – 1.58
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.006
- Other points: Inclusions, color.
Tourmaline
- Hardness: 7
- Specific gravity: 3.03
- Refractive index: 1.62 – 1.64
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.018
- Other points: Inclusions, color, pleochroism. There are many treated tourmalines in the gem market. Many
gem quality tourmalines are relatively clean. Analytical techniques may be required to detect treatments.
Topaz
- Hardness: 8
- Specific gravity: 3.53
- Refractive index: 1.63 – 1.64
- Optic sign: Biaxial positive
- Birefringence: DR; 0.008
- Other points: Inclusions, color (pink stones may be confused for pink sapphires). There are many treated
topaz in the market. Most gem quality stones are relatively clean. Analytical techniques may be required
to detect treatments.
Spinel
- Hardness: 8
- Specific gravity: 3.60
- Refractive index: 1.718
- Optic sign: SR
- Birefringence: -
- Other points: Inclusions, color, spectrum.
Garnet (pyrope)
- Hardness: 7.5
- Specific gravity: 3.78 (average)
- Refractive index: 1.75 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Garnet (almandine)
- Hardness: 7.5
- Specific gravity: 4.10 (average)
- Refractive index: 1.78 (average)
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Inclusions, color (may be confused for Thai ruby / synthetic ruby), spectrum.
Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to separate natural vs synthetic).
Synthetic Ruby
- Hardness: 9
- Specific gravity: 4 (average)
- Refractive index: 1.76 – 1.77 (average)
- Optic sign: Uniaxial negative
- Birefringence: DR; 0.008
- Other points: Inclusions, color, spectrum (use microscope to differentiate flux and hydrothermal).
Synthetic red cubic zirconia
- Hardness: 8.5
- Specific gravity: 5.65 +
- Refractive index: 2.15 +
- Optic sign: SR
- Birefringence: -
- Other points: negative refractive index, luster, color, orange flash on the pavilion, dispersion.
Red Zircon
- Hardness: 7.5
- Specific gravity: 4.69
- Refractive index: 1.93 – 1.99
- Optic sign: Uniaxial positive
- Birefringence: DR; 0.059
- Other points: Inclusions, color, spectrum, doubling of the back facets, dispersion, luster, negative refractive
index reading.
Red Diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Rare, negative refractive index reading, inclusions, luster, spectrum, dispersion. There are
many treated diamonds in the market. Most treated diamonds are relatively clean. Analytical techniques
may be required to detect treatments.
Synthetic red diamond
- Hardness: 10
- Specific gravity: 3.52
- Refractive index: 2.42
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Negative refractive index reading, color, inclusions, luster, spectrum, fluorescence. Synthetic
diamonds are produced by the high pressure high temperature method. Gem quality stones are relatively
clean. Analytical 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/ADR
- Birefringence: -
- Other points: Soft, inclusions (gas bubbles), color.
Assembled Stones
Doublets / Triplets
Corundum (natural crown / synthetic base)
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).
Synthetic spinel soude (spinel / spinel)
- Refractive index: 1.728
- Optic sign: SR/ADR
- Birefringence: -
- Other points: Look for differences in color and luster between the sections, gas bubbles).
Monday, January 15, 2007
Overweighing What Can Be Counted
Charles T Munger, Vice-Chairman of Berkshire Hathaway Corporation writes:
The late, great, Thomas Hunt Morgan, who was one of the greatest biologist who ever lived, when he got to Caltech, had a very interesting, extreme way of avoiding some mistakes from overcounting what could be measured, and undercounting what couldn't. At that time there were no computers and the computer substitute then available to science and engineering was the Frieden calculator, and Caltech was full of Frieden calculators. And Thomas Hunt Morgan banned the Frieden calculator from the biology department. And when they said, "What the hell are you doing, Mr Morgan?" He said, "Well, I am like a guy who is prospecting for gold along the banks of the Sacramento River in 1849. With a little intelligence, I can reach down and pick up big nuggets of gold. And as long as I can do that, I'm not going to let any people in my department waste scarce resources in placer mining." And that's the way Thomas Hunt Morgan got through life.
I have adopted the same technique. I haven't had to do any placer mining yet. And it begins to look like I'm going to get all the way through, as I had always hoped, without doing any of that damned placer mining. Of course if I were a physician, particularly an academic physician, I'd have to do the statistics, do the placer mining. But it's amazing what you can do in life without placer mining if you've got a few good mental tricks and just keep ragging the problems the way Thomas Hunt Morgan did.
The late, great, Thomas Hunt Morgan, who was one of the greatest biologist who ever lived, when he got to Caltech, had a very interesting, extreme way of avoiding some mistakes from overcounting what could be measured, and undercounting what couldn't. At that time there were no computers and the computer substitute then available to science and engineering was the Frieden calculator, and Caltech was full of Frieden calculators. And Thomas Hunt Morgan banned the Frieden calculator from the biology department. And when they said, "What the hell are you doing, Mr Morgan?" He said, "Well, I am like a guy who is prospecting for gold along the banks of the Sacramento River in 1849. With a little intelligence, I can reach down and pick up big nuggets of gold. And as long as I can do that, I'm not going to let any people in my department waste scarce resources in placer mining." And that's the way Thomas Hunt Morgan got through life.
I have adopted the same technique. I haven't had to do any placer mining yet. And it begins to look like I'm going to get all the way through, as I had always hoped, without doing any of that damned placer mining. Of course if I were a physician, particularly an academic physician, I'd have to do the statistics, do the placer mining. But it's amazing what you can do in life without placer mining if you've got a few good mental tricks and just keep ragging the problems the way Thomas Hunt Morgan did.
Diamond Cut: Escada Cut
The Escada cut is the creation of Pluczenik Group, the Antwerp-based master cutters and sightholders. The cut is trade marked and patented to the Pluczenik Group.
The Escada diamond jewelry concept is the result of innovative input from Italian luxury jewelry producer Crova and creative marketing by the De Beers Diamond Trading Company. The cut symbolizes the ever renewing cycle of 12 months of the year.
The cut is a 12-sided dodecagonal cut with unique geometry of facets. The 97-facet stones are difficult to cut. It requires the most advanced cutting techniques and technology.
All stones above 0.20carats will be identified with a laser inscription on the girdle and will be lab certified. The Escada logo will also appear on the shank of each ring.
The Escada Diamond Jewelry Collection is sold through Escada’s integrated distribution network at the company’s 365 stores in more than 50 countries and at high-end department stores.
The Escada diamond jewelry concept is the result of innovative input from Italian luxury jewelry producer Crova and creative marketing by the De Beers Diamond Trading Company. The cut symbolizes the ever renewing cycle of 12 months of the year.
The cut is a 12-sided dodecagonal cut with unique geometry of facets. The 97-facet stones are difficult to cut. It requires the most advanced cutting techniques and technology.
All stones above 0.20carats will be identified with a laser inscription on the girdle and will be lab certified. The Escada logo will also appear on the shank of each ring.
The Escada Diamond Jewelry Collection is sold through Escada’s integrated distribution network at the company’s 365 stores in more than 50 countries and at high-end department stores.
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