• Atomic Number: 6

• Atomic Weight: 12.011

• Outermost Electron: 4

But the diamond is distinctly different from its close cousins the common mineral graphite and lonsdaleite, both of which are also composed of carbon. why is diamond the hardest surface known while graphite is exceedingly soft? Why is diamond transparent while graphite is opaque and metallic black? What is it that makes diamond so unique?

The key to these question lie in diamond's particular arrangement of carbon atoms or its crystal structure.

Crystal Structure

A neutral carbon atom has 6 protons and 6 electrons surrounding its nucleus. Four of the electrons in a carbon atom are valence electrons, which are electrons that are available to form bonds with other atoms. In graphite, each carbon atom bonds only 3 of its 4 valence electrons with neighboring carbons. The resulting structure of these bonds is a flat sheet of connected carbon atoms. Though individually strong, these layers are only weakly connected to one another, and the ease with which they are separated is what makes graphite so slippery.

In diamond, however, every carbon shares all 4 of its available electrons with adjacent carbon atoms, forming a tetrahedral unit. This shared electron-pair bonding forms the strongest known chemical linkage, the covalent bond, which is responsible for many of diamond's superlative properties. The repeating structural unit of diamond consists of 8 atoms which are fundamentally arranged in a cube.

The diamond structure shows how each atom(red ball) is connected to 4 other carbon atoms by strong chemical bonds, creating diamond's rigid crystal structure.

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Dodecahedron

Macle twin

Diamond Crystal

​​Real diamond crystals don't have completely smooth faces. Trigons are triangular growths that reflect subtle changes in height on a diamond's face. The trigons shown here are slight indentations that were most likely produced by a natural etching of the crystal. However, raised trigons, which point in the same direction as the crystal face, may also occur from etching, dissolution, or as part of the natural growth of the crystal.

Fluorescence

and Phosphorescence

This simplified diagram shows the conditions of pressure and temperature where diamond and graphite will be the stable forms of carbon. The points show the conditions at which diamonds were first grown by the companies ASEA and General Electric in the early 1950s. Temperatures are in Kelvin--subtract 273 to convert to degrees Celsius.

This magnitude of pressure is difficult to comprehend. For example, the pressure of 55,000 atmospheres necessary to make a diamond at 1400 degrees C (orange hot) would require: the Eiffel Tower (7000 metric tons) resting on a 5 inch plate.

An interesting property of some diamonds is that they can glow in the dark. When illuminated by ultraviolet light, certain diamonds can absorb the high-energy radiation and re-emit it as visible light. These diamonds are called fluorescent. Some can even continue glowing after the ultraviolet source is turned off. These diamonds are phosphorescent.

All diamonds do not fluoresce, only about 30% of diamonds exhibit some degree of fluorescence. Most diamond grading laboratories consider diamond fluorescence an identifying characteristic but it is not a grading factor 4Cs. Just report and describe a diamond's fluorescence by its intensity as like 'None, Faint, Medium,  Strong and Very Strong. Some experts of diamond think blue fluorescence enhances a diamond's color, especially diamond whit I to  M color grades. This blue fluorescence can make a faint yellowish diamond with a very strong to medium bluish fluorescence may have a slightly higher color grade than similar diamonds that do not fluoresce.