Colors :- The Aurora collection of 296 diamonds consists of diamonds belonging to 12 different varieties of pure colors. These colors are blue, green, olive, yellow, brown, orange, red, pink, purple, black, gray and white. The collection also contains diamonds of modified colors which perhaps may include several of the following combinations :- grayish blue, purplish pink, orange pink, brownish pink, purplish red, brownish red, yellowish brown, orange brown, brownish yellow, brownish orange, pinkish purple, brownish purple, grayish purple, yellowish green, bluish green etc. Average size :- Most of the diamonds in the collection are less than one carat in weight.
Shapes :- The shapes of the diamonds included all possible shapes in which diamonds are cut in the diamond industry today, such as round, oval, cushion, pear, marquise, heart, trillion, emerald, asscher, princess, radiant etc.
Types of diamonds :- The diamonds in the collection belonged to all the different types and sub-types in the classification of diamonds.
The near-colorless (G-J), faint yellow (K-M), very light yellow (N-R), light yellow (S-Z), fancy light yellow and fancy yellow diamonds in the collection, are all Type Ia diamonds, in which the color is caused by nitrogen atoms found as aggregates of 2, 3, or 4 atoms, known as A-aggregates, N3 centers and B-aggregates respectively. A & B aggregates do not affect the color of diamonds, but N3 centers do. Almost 98 % of naturally occurring diamonds are Type Ia.
The darker shades of yellow such as fancy intense yellow, and fancy vivid yellow including the canary yellow, and the different shades of orange are Type Ib diamonds, caused by single nitrogen atoms scattered in the crystal. Only 0.1 % of naturally occurring diamonds are Type Ib.
Nitrogen atoms absorb visible light in the blue region of the spectrum, causing its complementary color yellow to appear. Very rarely nitrogen atoms absorb visible light in the green region of the spectrum causing its complementary color orange to appear.
The absolutely colorless diamonds (D-F), are Type IIa diamonds, in which the colorless nature results due to the absence of factors that cause color in diamonds, such as chemical impurities, and structural abnormalities. Their occurrence is 1-2 % of all naturally occurring diamonds.
Pink, red, purple, and brown colored diamonds are alsoType IIa diamonds in which the color is caused by the plastic deformation of the crystal structure. There occurrence however is less than 0.1 % of all natural diamonds. The occurrence of plastically distorted brown diamonds is very high in the Argyle diamond mines, and accounts for almost 80 % of the production of gem quality diamonds
Green diamonds are also Type IIa diamonds, in which the green color is caused by the exposure of diamonds over long periods of time to natural radiation like alpha, beta and gamma radiation, which alters the structure of the diamond, producing the green color. The occurrence of green diamonds is less than 0.1 % of all naturally occurring diamonds.
Blue diamonds are Type IIb diamonds, in which the presence of trace quantities of boron impurities in the crystal structure of the diamond imparts the blue color, as well as semi-conducting properties to the diamond. Their occurrence is less than 0.1 % of all naturally occurring diamonds.
Black diamonds are in a class by themselves and not classified with other diamonds. Black diamonds are not made up of large single crystals like conventional diamonds, but are aggregates of millions of tiny crystals. They are porous and contain trapped gases. They are harder than conventional diamonds, and are difficult to cut and polish. However there may be softer areas within the crystal, that results in large losses when attempting to cut a black diamond. The black color is caused by iron compounds like hematite and magnetite associated with the crystals. Another important fact about black diamonds is that they do not originate in lamproite and kimberlite pipes like the conventional diamonds. Scientists of the Florida International University has proposed an extra-terrestrial origin for black diamonds, found only in Brazil and the Central African Republic.
