Diamond

Diamond is the most precious of the gemstone. The word “Diamond” originally comes from the Greek word “Adams” which means “Unconquerable”.
Diamonds are formed by nature in the upper mantle of the earth’s crust. Crystallization took place millions and millions of years ago, under enormous pressure and at a very high temperature. Before being forced to the surface of the earth, they were stored in the upper mantle of the earth at a depth of 150-300km below the surface. The atoms in diamond are equidistant from one another.
Graphite and diamond both are the forms of carbon but with highly diverse properties. Diamond is the purest crystalline transparent form of carbon whereas charcoal, soot and coke are non-transparent and non-crystalline impure form of carbon. Diamond is bad conductor of electricity.
It is not surprising that rough diamonds are never completely free of impurities or irregularities in crystal structure. Growth of environment, chemical impurities can cause structural distraction; they can even scatter the crystal. In diamonds color vary so widely, sometimes it becomes difficult to judge the exact color.
Sine time in memorial up to 2600 minerals has been found in the earth’s crust, out of which one is diamond. Among all the minerals diamond is the hardest but not toughest (Jade is the toughest mineral of all), uncompressible, durable and indestructible gemstone. Only diamond can cut diamond. Diamond can withstand high temperature and great pressure but cannot withstand heavy hammering due to weak toughness. Diamond is brittle in nature. From where there is cleavage, diamond can be cleaved. Diamond’s original color can neither be changed nor destroyed. Diamond reflects light, and it is maximized with the cut.
In times of economic and monetary instability diamond has a very significant role to play. Acids and alcohol cannot change any of the properties of diamond like luster etc. Because of its size and value, diamond is the most valuable substance known. Diamond cannot be seen in the dark, because it doesn’t reflect its own light.
In astrology each gemstone represents different planets in the universe, diamond represents the planet Venus.

Properties

Chemical Composition: 

Carbon - C

Structure: 

• 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.

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.

Colors / Varieties: 

• All colors (transparent to opaque)
• Cryptocrystalline varieties: Bort, Carbonado, etc.
• Chameleon Diamond: Golden yellow in the dark which changes to gray green when exposed to light.

Crystal System / Forms: 

Cubic System / Variable octahedron, cube, dodecahedron, twinned macle and combination of cubic forms.

Hardness: 

10 (directional hardness variation)

Specific Gravity: 

3.515; crypto-crystalline carbonado 2.9 - 3.5

Cleavage / Fracture: 

Perfect octahedral cleavage / step like fracture

Optic Character: 

Isotropic

Lustre: 

Adamantine

Refractive Index / Birefringence: 

2.417

Pleochroism: 

Nil

Dispersion: 

0.044

Magnification: 

• 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.

U.V. Fluorescence: 

1. Colorless to yellow diamonds (cape series): Blue or yellow under ultra violet lamp. Natural colorless diamond exhibits blue under longwave while Synthetic colorless diamond generally exhibits blue under shortwave. Synthetic yellow diamond exhibits green in shortwave.
2. Brown: Green to greenish yellow under ultra violet lamp.
3. Pink: Variable; exhibits orange under ultra violet lamp.
4. Some diamonds exhibit phosphorescence.

Spectrum: 

1. Colorless to yellow diamonds (cape series): Lines at 415nm, 423nm, 435nm, 452nm and 478.5nm.
2. Brown: Lines at 503nm, 537nm and 495nm
3. Pink: Line at 415nm and a diffused band at 550nm
4. Treated yellow, green, brown, pink have characteristic spectrums.

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.

Treatment (Enhancement): 

1. Coating / Spraying: Blue color is sprayed just below the girdle in yellow tinted diamonds to neutralize the yellow color and make it appear whiter.
2. Colorless Impregnation: Fracture filling is done using lead glass to improve the clarity. It is identified by color flashes (blue / green / orange / pink) along cracks, diversification effects, etc.
3. Lasering: With the help of laser rays, dark colored impurities are removed by drilling holes to the impurity and leaching it out. It maybe filled with lead glass and sealed and identified by color flakes along the drill hole. A new technique KM treatment expands the inclusion to the nearby cleavage crack / feather, which is then leached out with the help of acids. The treatment is virtually impossible to detect conclusively.
4. Heating / Irradiation:
   1. Gamma rays produce a uniform blue-green color which on heating becomes dark green.
   2. Similarly using electrons, neutrons, protons, etc. various colors are obtained.
   3. Identification in case of cyclotron treated diamonds shows a dark ring within the girdle, umbrella effect (zone of color near the girdle).
   4. Spectroscopy is commonly preferred for the identification.
   5. Poor quality brown diamonds are exposed to high temperature of 900° to 1600° so that the diamond portions nearer to the cleavage / features turn to graphite giving black body color to the stone. The process is known as 'Graphitization' the treatment can be identified by observing the concentration of black / gray dots along the cracks or feathers.

Specific Tests & Remarks: 

This test is applicable only to well proportion round brilliant cut diamond.

1. • 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.
2. 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.
3. 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.
4. 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).

Synthesis: 

• Flux fusion using belt apparatus and split sphere techniques.
• Carbon Vapor Deposition (CVD) Method

Identification of Synthetic Diamonds

1. Microscopy: Color zoning and graining (rectangular / square / octagonal), metallic inclusions (iron, nickel)
2. U.V. Lamp: Green under longwave and yellow under shortwave.
3. Spectroscopy: Moderate absorption band between 450nm and 500nm, weak bands between 470nm and 600nm.
4. Reactions to diamond view and diamond sure.
5. 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

Simulants (with key 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).

Geological Occurrence: 

Found in kimberlite (a type of peridotite rock), sometimes in lamproitic rocks. In pipe deposits, alluvial, eluvial and marine deposits.

Sources: 

Africa (South Africa, Zaire, Botswana, Sierra Leone, Namaqualand, etc.), Australia, India (Madhya Pradesh, Andhra Pradesh, Orissa, etc.), China, Russia, Brazil, etc.

Cuts & Uses: 

Facetted cuts, beads, etc.