Diamond and alexandrite are two of the rarest gemstones on Earth. A diamond is created due to extreme temperature and pressure on carbon deep underground. Alexandrite, named after the Russian Tsar Alexander II in April 1834 when it was discovered in the emerald mines in the Urals, is even more rare than diamond due to the unusual combination of minerals that form it. These minerals include titanium, iron and chromium, which give alexandrite the rare quality of changing colour in changing light, from green to purple.
Natural versus Synthetic Stones
Technology has enabled jewellers to create synthetic versions of both diamond and alexandrite, but the real value is in natural stones. Natural alexandrite is very rare, and therefore extremely valuable. Up until 1987, the only source of alexandrite was in Russia, until new alexandrite deposits were discovered in Brazil. Diamonds are much more prevalent, with Botswana, Russia and Canada responsible for over 18,000,000 carats each per year.
Clarity describes the absence or presence of a gemstone's flaws, which are referred to as inclusions. There are different reasons for inclusions, such as a crystal in the stone, or lines that can be grainy or feathery. Diamonds and alexandrite are rated almost on the same scale. The most expensive diamonds can be termed flawless. They are created from one mineral, carbon. If they are said to be included, it means they are flawed to some degree.
Because coloured gemstones are always a combination of more than one element, flaws will always be present. VVS is the rating for very very slightly included. The scale continues with VS, Very Slightly; SI1 and 2, Slightly Included; then I1, 2 and 3, Included. I3 would be the most flawed and therefore least desirable stone, but still of value, especially if it is alexandrite.
Cut used to refer to the shape of the gemstone, but jewellers now evaluate the stone's overall proportions and how the cut enhances the brilliance of the stone. Stones can be cut in a variety of shapes, but the more facets, the more valuable the stone will be. The cut is up to 30 per cent of the value of a stone, so a bad cut can be very costly.
The shape of a gemstone can be anything from square cut to cushion to pear drop or heart, depending on the nature of the stone and the facets the gem cutter is trying to bring out through his work. The more intricate the cut for a diamond or alexandrite, the more expensive the stone.
Carat is the term used to express the weight of a diamond, with one carat equalling 200 milligrams of actual weight--about the same weight as a small paper clip. Any alexandrite over one carat is extremely rare and will be far more valuable than a diamond of the same size.
Green diamonds are quite rare compared with colourless stones and diamonds in other colours. They are comparable in terms of beauty, but do not have the duality of colouring that alexandrite acquires depending on the light. Purple diamonds are also rare, and likewise do not have the duality of colouring of alexandrite.
Alexandrite is valued in terms of both of its colours. When discussing its main colour, green, visible in natural light, hue and saturation are evaluated. These terms refer to how green the stone is, with either hints of yellow or blue, and how deep the colouring of the stone appears, from nearly see-through to deep green. The same assessment will be used for its secondary colour, which can range from a lavender grey to red or even brown, with purple as the most desirable colour. The saturation can range from pale purple to a deep violet colour.