Getting to know Diamonds
Diamonds are formed by the transformation of carbon into pure carbon. This process takes billions of years to occur, at very high pressure (at depths of more than 70-150 km) and temperature (over 1300°C).
Only a small quantity of the diamonds extracted from the mines is destined for jewelry, and of this quota only a very few are high quality gems larger than one carat.
Diamond features the highest hardness of any naturally occurring material. On the Mohs scale of mineral hardness (from 1 to 10) it is the hardest (10), followed by corundum (9) that are 140 times less hard.
Another typical property of diamond is its very high refractive index (2.42).
These two features lead non-experts in gemology to confuse diamonds with synthetically produced moissanite (silicon carbide) because it is 35 times harder than corundum and has a refractive index that is higher than that of diamond (2.65).
Moissanite is birefractive (diamond is singly refractive), and this allows experts to distinguish it from look-alikes without the need for gem analysis. The market offers other diamonds with the same hardness (10) and refractive (2.42) indices of natural diamonds. These are synthetically produced in laboratories and are known by special names – CVD, Chemical Vapor Deposition and HPHT, High Pressure High Temperature. They can be distinguished from natural diamonds only when tested using special instruments.
The gemologist analyses the gem based on the ‘4C’s’:
Carat – Clarity – Color – Cut
Carat (ct.) is the weight metric used for precious gems. One metric carat amounts to two-tenths of a gram and is divided into 100 points (one point is one hundredth of a carat).
Clarity, the clarity scale is divided into:
P3 or I3, P2 or I2, P1 or I1 (inclusions visible to the naked eye),
SI2, SI1 (inclusions visible under x10 magnification – barring rare exceptions),
VS2, VS1 (very small inclusions difficult to see under x10 magnification),
VVS2, VVS1 (very very small inclusions difficult to see under x10 magnification),
IF (internally flawless),
FL (flawless both inside and out).
Color in a diamond is determined by the presence of atoms other than carbon that remain trapped in the diamond’s crystal structure during formation. The most common diamonds contain nitrogen atoms that give each diamond its color that can range from colorless to more or less intense yellow/brown tones, based on the distribution of the atoms.
D, E, F, G, H, I, J, K, L – Z
(the most desirable colours are D, E or F.)
Cut Diamonds can be cut in different ways: round brilliant, oval, emerald, heart, marquise, princess, pear as well as other fancy shapes. The round brilliant diamond cut is the one most commonly seen because it refracts light in the most desirable way. A round cut consists of 56 facets plus the table, distributed between the diamond’s crown and pavilion.