April’s birthstone is unique and beautiful diamond. The most popular and one of the most valuable gemstones, diamond is famously ‘a girl’s best friend’. No gemstone is more advertised or more likely to be seen adorning the bodies of the rich and famous. It can be found in jewellers on every high street, so what makes this gemstone so special?
Diamonds form at much greater depths within the Earth than other gemstones, where conditions are extreme. The only reason that we can access them is because volcanic activity brings them closer to the surface. They are formed entirely of carbon (they are the only gem material formed exclusively of a single element), which at surface temperature and pressure forms as graphite. Under the extreme temperatures found deep within the Earth, the atoms bond differently and diamond is the result: it is incredible how different the two materials are!
Diamond has a unique combination of brilliance and fire, and unparalleled bright adamantine lustre. The round brilliant cut was specifically developed over generations to show off these features to their best advantage. Brilliance is the bright return of light by a gem and is a combination of reflections from the internal surfaces of the pavilion (bottom of the stone) and the external surfaces of the crown (top of the stone). Fire is the flashes of spectral colours seen when the gem disperses light: splitting it into its separate colours in a similar way to a prism. Diamond produces a significant amount of dispersion, which coupled with its intense brilliance and lustre, gives it a distinctive appearance unlike that of any other gemstone.
The other unique feature of diamond is its hardness and ability to resist scratching. Hardness in gemstones is measured on the Mohs’ Scale which allocates a hardness value between 1 and 10 to materials based on their relative hardness. The scale is not linear and simply demonstrates that one material is harder than another. Diamond is the only gemstone with a hardness of 10. Sapphires and rubies are 9 on the scale, but the difference in hardness between them and diamond is greater than the difference between them and talc which has a hardness of 1. Diamond’s exceptional hardness means it can be worn for decades and still maintain its lustre without scratches or worn facet edges. In this sense diamonds really are forever!
It is worth bearing in mind that although diamonds are incredibly hard, they lack toughness in comparison to some other materials. It is therefore possible to chip or break a diamond even though it is very difficult to scratch it. This is due to the structure of the material; diamond has a very organised and tightly packed structure. The atoms are bonded tightly together, but there are more bonds in some directions and less in others; this causes those directions with less bonds to be comparatively slightly weaker, and along these planes it is easier to break apart the structure. This property is known as cleavage. If a diamond is struck with force in the wrong direction it is possible to break it, although this does not happen easily!
Diamonds are most famous for their pure colourless appearance, but they do form in a wide range of colours including yellow, blue, pink, green, black, brown and red. These colours can be caused by a variety of reasons such as the presence of additional elements as impurities within the gem, defects in the crystal structure or exposure to radiation. They are known as fancy colours and are rarer and more expensive than colourless diamonds in most cases (black and brown being exceptions). Most fancy colour diamonds that you will see have been enhanced using irradiation and heat treatments; natural fancy colour stones with vivid colours can be among the most expensive gems on the planet.
Diamonds can vary hugely in quality and are graded for their colour, clarity and cut. This can have a significant impact upon price as well as helping you to understand what you are buying. You can read more about these factors in our series of blogs ‘Choosing Your Diamond’. If you have any more questions about this incredible gemstone then our team of highly qualified gemmologists and diamond graders will be happy to share their knowledge with you. You can view a wide range of diamond jewellery on our website and even more stunning items can be viewed in our showroom.