Cause of Color :
- Yellow: Nitrogen and related color centers.
- Blue: Boron
- Green: Color center due to natural or artificial irradiation.
- Other colors are due to trace elements and related color centers.
Chemical Composition :
Carbon – C
Classification / Type :
Diamonds are classified Type 1 and Type 2 on the basis of elements in the structure which give rise to varying properties / color. Types of Diamonds:
- Type 1: Contains nitrogen which is subdivided into Type 1a and Type 1b.
- Type 1a: Nitrogen as clusters. Most natural diamonds fall in this type. It is further sub-divided into Type 1aA and Type 1aB depending on the arrangement of nitrogen atoms with or without a vacancy.
- Type 1b: Nitrogen is present in a single state as foreign atoms. Almost all synthetic diamonds and a very small of natural diamonds fall in this type.
- Type 2: Contains hardly any nitrogen but contains other elements which are subdivided into Type 2a and Type 2b.
- Type 2a: No appreciable nitrogen, generally brown, pink and colorless.
- Type 2b: Contain boron and as a result such diamonds are semi-conducting. Generally blue diamonds.
Crystal System / Forms :
Cubic System / Variable octahedron, cube, dodecahedron, twinned macle and combination of cubic forms.
Cuts & Uses :
Facetted cuts, beads, etc.
10 (directional hardness variation)
- External features: Naturals, nicks, pits, scratches, polishing lines, damaged culet, etc.
- Crystalline fingerprints or inclusions of Olivine, graphite, garnet, diopside, spinel, diamond, etc.; fingerprints
- Structural inclusions: Twin planes (knots), grain lines, fine cleavage cracks (bearding) along girdle.
Optic Character :
Refractive Index / Birefringence :
Simulants (with separation tests) :
Synthetic Moissanite (doubling, dispersion, inclusions), Zircon (optic character, spectrum, doubling), Strontium Titanate (dispersion, S.G., inclusions), Y.A.G. (S.G., dispersion), G.G.G. (S.G., lustre), Synthetic Rutile (optic character, dispersion, doubling), Natural / Synthetic Sapphire (optic character, lustre, dispersion), Doublets (inclusions, lustre).
Africa (South Africa, Zaire, Botswana, Sierra Leone, Namaqualand, etc.), Australia, India (Madhya Pradesh, Andhra Pradesh, Orissa, etc.), China, Russia, Brazil, etc.
Specific Tests :
This test is applicable only to well proportion round brilliant cut diamond.
- Read through effect: When placed table down on written matter and viewed from above the girdle, will not exhibit a read through effect.
- This is due to the proportioning with respect to total internal reflection.
- Surface tension: This property is defined when ‘Ink’ is used. A line drawn across the surface with a diamond pen will remain as an unbroken line in a diamond but will bead up in a simulant.
- X-ray transparency: Transparent to x-rays due to lower atomic mass (atomic mass = 12). When x-ray is passed at 90° to the surface of the diamond it will pass through it but at angles other than 90° it will flourish which is due to the structure of diamond.
- Thermal Conduction::
- Single crystal diamond varies from 1000 watts/m/°C for Type 1 to 2600 watts/m/°C for Type 2a.
- This is measured with the help of a thermal probe and is also observed in the age old property of the Breath Test (when you blow on a diamond, the condensed moisture droplets evaporate quickly as compared to its simulants).
- Colorless to yellow diamonds (cape series): Lines at 415nm, 423nm, 435nm, 452nm and 478.5nm.
- Brown: Lines at 503nm, 537nm and 495nm
- Pink: Line at 415nm and a diffused band at 550nm
- Treated yellow, green, brown, pink have characteristic spectrums.
- Tetrahedral structure with each carbon atom, which is in the centre of a tetrahedron, covalently bonded to four other carbon atoms.
- Bond lengths are 1.54 Angstrom unit giving rise to strong atomic bonding and therefore the hardness and stability in a diamond.
- Flux fusion using belt apparatus and split sphere techniques.
- Carbon Vapor Deposition (CVD) Method
Identification of Synthetic Diamonds
- Microscopy: Color zoning and graining (rectangular / square / octagonal), metallic inclusions (iron, nickel)
- U.V. Lamp: Green under longwave and yellow under shortwave.
- Spectroscopy: Moderate absorption band between 450nm and 500nm, weak bands between 470nm and 600nm.
- Reactions to diamond view and diamond sure.
- Types of Synthetic Diamonds
- Synthetic Yellow Diamond: Type 1b
- Synthetic Blue Diamond: Type 2b or mixed with Type 2b + Type 2a
- Synthetic Colorless Diamond: Type 2a or mixed with Type 2a + Type 1b + Type 2b