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Diamonds are the hardest mineral form of carbon. Carbon is present on earth in two forms: diamonds and graphite. Graphite is a soft greyish-black mineral, whereas diamond is a hard and colourless form of carbon. They are found naturally on earth, and it is the hardest naturally present substance and most popular gemstone. They are weighed in carats.1 carat
= 200 milligrams. They are formed under high pressure and temperature in the earth’s mantle.
The structure of the diamond is octahedral. Each carbon atom is bonded to four other carbon atoms. They are present in the crystal form, and face-centred crystal lattice is present in the diamonds.
Types of diamonds
Diamond is categorised into two types based on the nature of impurities present in them:
Type I:
These diamonds contain nitrogen as the main impurity. The concentration of nitrogen can be 0.1%. They are further divided into three types:
Type IaA: In this, the nitrogen atoms are present in pairs, so it does not affect the colour of the diamond.
Type IaB: In this type, the nitrogen atoms are present in even numbers, which give it a yellow to brown tint.
Type lb: In this type, the nitrogen atoms are present in a free state. They are dispersed in the whole crystal, not present in groups. This gives the diamond a yellow colour or sometimes brown.
Type II:
The diamonds categorised in type II have an unknown amount of nitrogen impurities. They can be of colour brown, pink, and red, according to the structural abnormality.
Type IIb: It is one of the diamonds used as a gem and is normally present in light blue colour due to the mixing of boron.
Type lla: They are blue-grey.
Colours in diamonds
Diamonds occur in various colours such as grey, brown, white, yellow, brown, pink, red, blue, etc. The colour of a diamond is due to impurities and structural defects in it. Pure diamonds are always colourless and transparent.
Brown and yellow colour diamonds:
The impurity of nitrogen gives the diamond a brown and yellowish colour. The colour is based on the percentage of presence of nitrogen. There are two conditions for these colours.
- Suppose the nitrogen percentage is higher and present in even numbers in the lattice. In that case, it will be yellow to tinted brown.
- Suppose the nitrogen atoms are all over the crystal, individually, not in pairs or groups. In that case, the colour will be extreme yellow to brown.
White colour diamonds:
The white colour diamonds are translucent and opaque in appearance. The colour is due to the presence of clouds, which are fine and reflective, giving it a white colour.
Pink or red colour diamonds:
These colours are due to the abnormality in the structure of the diamond. When too much stress is caused by the earth, due to which the displacement of carbon in the diamond crystal. Transmission of light gives it a pink colour.
Red colour diamonds are the most valuable diamonds. Strong transmission of red wavelength causes the colour of diamond red.
Orange colour diamonds:
They are very rare diamonds. The transmission of orange colour and absorption of blue colour, given it orange colour.
Green colour diamonds:
They are also very rare in nature. The green colour of the diamond is due to the presence of impurities such as hydrogen, nickel, or nitrogen. The presence of green diamonds is also due to the emission of green light and absorption of red light.
Blue colour diamonds:
Blue colour diamonds: is often caused due to presence of boron atoms in the lattice of a diamond. A tiny quantity of boron can cause noticeable blue colour.
Violet colour diamonds:
It is the rarest colour in the diamond. It is caused by the presence of hydrogen atoms in the crystal lattice of the diamonds.
Purple colour diamonds:
This colour is also the rarest in diamonds. The colour purple or sometimes pink is caused due to the displacement of carbon atoms.
Black colour diamonds:
Naturally, the black colour in diamonds is due to the high concentration of minerals, which causes the passing of very little light through it. These diamonds are translucent or opaque.
Conclusion
Diamonds are costly and natural minerals. They are composed of carbon. Pure diamonds have no colour, but due to the presence of impurities, they become of different colours. They can be brown, yellow, pink, red, black, and violet. There are two kinds of diamonds present based on the presence of impurities in them:
- Type I
- Type II
