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Diamond World Data

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Jabotinski St., Ramat-Gan 52520, Israel

 


Diamonds basics

Diamond is one of the molecular forms of carbon (defined as the element C) and occurrs in the basic form of a tetrahedral structure in which each carbon atom is in the center of a tetrahedron and is chemically bonded to 4 other carbon atoms in the edges of the tetrahedron. 

 

 

 

 

 The basic structure of a diamond

 Diamond structure

The basic structure of a diamond

 Diamond structure


As can be clearly seen in the figures the basic steric structure is of a tetrahedron and the tetrahedron structure is repeated in the macrostructure of the diamond.

 

This structure is a very stable basic unit with strong chemical bonds which results in the hardest material known. It is very stable under high pressure conditions and in order to decompose it one needs to heat it to very high temperatures, exceeding 3,500oC. However if one heats the diamond in the presence of oxygen (like air which is a mixture of several gases and contains ~21% oxygen) it will react with the oxygen and will form carbon dioxide CO2.

 

Furthermore, it is very stable under high pressure but at atmospheric conditions it is not stable and if it is heated in the absence of oxygen to 1,200oC it will be converted to a more stable form of carbon known as graphite.


Under atmospheric pressure graphite is much more stable as the molecular form of carbon.


 The basic structure of graphite

 

 

 

 Graphite structure

 The basic structure of graphite

 Graphite structure

 

Graphite's basic structure is composed of a layer of hexagon rings (a ring consisted of 6 carbon atoms) and the rings are connected to each other forming the layer. The graphite contains many such layers hooked between them by weak bonds. Graphite is a very good heat and electric conducting material.


As the diamond is the stable form of carbon only under very high pressure, this is the reason that at depths of 100-150 km under the earth's surface (very high pressures) most carbon abundant is in the form of diamonds. At this depth the temperature reaches 1,000-1,200oC and it takes millions of years for the carbon atoms to move and form the diamond structure. Diamonds are ejected to the earth's surface via volcanic eruptions

 Diamond ejection to earth

 Diamond ejection to earth's surface via a volcanic eruption


and if they are cooled to room temperature before the diamond has reacted with the atmospheric oxygen to for the gaseous carbon dioxide they will stay as such without converting to graphite the more stable form of carbon at atmospheric pressure. During the cooling process a matte layer is formed on the surface of the diamond and the outside appearance of the rough diamond (before polishing) is that of a small pebble. Most of the diamonds contain some fractures, graphite centers, inclusions etc. and thus are not fit for the jewelry industry and are used for the cutting, polishing and drilling industry. The fractures stem from the mining process which involves mechanical stress induced on the diamonds. The source of this is because of rock detonations and grinding of the rock during the separation of the rough stones from the rock.


As stated above the diamond is a very stable and also the hardest material known. It is also very stable chemically and does not react with the most active oxidizing chemicals like aqua regia, sulfuric acid. Also up to 600-700oC it does not react with oxygen and in the absence of oxygen it is not transformed into the more stable graphite form at temperatures lower than 1,200oC.


Furthermore diamond has a very high index of refraction and white light passing through a diamond will be separated to the full visible light and produce flashes of colored light (known as fire of the diamond). However one should remember that a diamond should be polished in order to eliminate the outer layer of rough stone, which is not transparent to visible light and does not allow any separation of the white visible light to it's colored components creating it's fire. Also fluorescence processes in diamonds which are exposed to UV (ultraviolet) radiation is observed in some diamonds. This might/might not affect the fire of the stones. Blue, orange, green and yellow fluorescence's have been observed as is image below.

 

 ×¦×™×œ×•× של יהלומי גלם

 ×¦×™×œ×•× של יהלומים עם פלואורסצנסיה כחולה, ירוקה כתומה וצהובה

 Diamond rough stones

 Fluorescence process in diamonds exposed to UV light. rough stones

 

 
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