Aquamarine – the beautiful blue birthstone of March
Aquamarine, as the name suggests, is a gemstone that has long been associated with sailors and the sea. For many centuries aquamarine was thought to have protective powers and the ability to improve a person’s health. Aquamarine is the birthstone of March and in recent years it has become an increasingly popular choice for engagement rings. The stone can actually be found in a range of hues from ocean blue to blue-green and it can compliment other gemstones very well. Aquamarine is positioned roughly in the middle of the gem pricing spectrum but the best aesthetics are achieved with larger carat examples. In recent years synthetic aquamarine has become more common and these stones can represent an opportunity for buyers that are on a budget. Akin to emerald, aquamarine is a member of the beryl family and its colouration is derived from iron speciation in the crystal. Unlike most coloured gemstones the true value of an aquamarine is derived mainly from its tone rather than its hue or saturation – the darker the stone the higher its premium. Stones that are sometimes referred to as “white aquamarine” are not actually aquamarine at all and are in fact goshenite or colourless beryl. Aquamarine tends to have a 5-30% green hue and heat treatment can successfully remove any yellow colouration and enhance the blueness of the stone. Despite the general market preference for stones that are as blue as possible, some collectors actually prefer examples with a hint of “sea-green” colouration.
(Aquamarine crystals derive their unique colour from iron speciation in the host rock)
When it comes to cutting and polishing aquamarine, faceting should only be carried out on eye-clean specimens (VS or better in GIA parlance). Any visible inclusions will substantially reduce a stone’s value and some highly transparent examples display a highly sought after ‘icy’ quality. Due to the fact that it is the tone of an aquamarine which has the greatest influence on its value, cutters aim to shape them so as to enhance this quality over all others and tend to favour the emerald cut. Unusually among gemstones the price per carat of aquamarine does not increase exponentially, as it does with many of its peers. In fact it starts to drop above 25 carats, the generally accepted limit for jewellery creation. Above this size they tend to be used for carving. There are some examples of extremely large carved aquamarine, including the 10,363 carat “Dom Pedro Aquamarine 1,” the largest in the world, which was produced in Minas Gerais, Brazil and is now housed in the Smithsonian Institute Museum of Natural History, Washington D.C. Generally aquamarine of over 5 carats tends to be darker and hence the 5-25 carat range contains the most desirable stones. Most rare of all are star and cat’s eye aquamarine, which display asterism and chatoyancy (a band of bright lustre caused by reflection from hollow inclusions in the stone) respectively. Star aquamarines are the most highly prized of all but cat’s eye cabochon can also fetch a premium, setting their value close to some of their faceted peers.
(“Dom Pedro Aquamarine 1” – the largest example in the world, which is housed in the Smithsonian)
As with many coloured stones, heat treatment is commonly applied to aquamarine, where it is specifically targeted at the reduction in yellow hues and the deepening of the shades of blue. The outcome of this treatment varies quite widely and often depends open the gem’s provenance and chemical composition. The results are permanent but they do not fade or change in any way over time so no special care is needed. Some aquamarine will not respond to heat at all, due to the nature of their crystalline structure and the geochemistry of their origin. It is important to note that some aquamarine are synthetic and grown hydrothermally in a lab, often resulting in stones that are very difficult to discern from their natural peers. Only scientific certification in a gemmological laboratory can conclusively determine synthetic from natural stones with total certainty. Maxixe aquamarine, named after the Maxixe mine, Minas Gerais, Brazil, are blue beryl that achieve their colour from irradiation in the lab, rather than by the natural presence of iron in their growth rocks. Unlike heat treated aquamarine, these stones are unstable and do fade in colour over time but they are easily identified under laboratory conditions. It is also possible to source synthetic spinel that display deep aquamarine colours and these stones are far more reasonably priced and often exhibit vibrant colour. Zircon can also be heat treated and topaz irradiated to display an “aquamarine” blue but these stones do chip very easily and are difficult to facet into some cuts.
Many stones are sold as aquamarine simply because they resemble their distinctive colour so it is very much a case of buyer beware! A key give away are stones that are priced well below the point at which you would expect to find them for their quality. Unlike their sister beryl emerald, the provenance of an aquamarine tends to have a less profound effect on its value. The majority of the famous mines are located in Brazil’s Minas Gerais district but fine examples are produced elsewhere and dealers tend to pay more attention to the colour of the stone and its clarity, rather than its source. Most people are now familiar with the GIA diamond grading categories but quality descriptions for aquamarine are a little harder to accurately pinpoint. As a result, many sellers have developed their own grading system and often refer to stones as being AAA, AA or A, for example. However, this can be a little misleading and may, of course, be manipulated to the advantage of the seller! Certification is the key tool in the arsenal of the non-professional buyer and it is very important to study the stone’s certificate carefully. Pay particular attention to any indications of clarity and/or colour enhancement, as these can affect the value. Enhancement is a widely practiced, and commonly misunderstood, process in the coloured gemstone world and in itself it shouldn’t prevent you buying a particular stone. The key is to ensure that a stone you purchase has been priced at an appropriate level to its colour and clarity and you must always remember the age old adage that if it is too good to be true, it probably is!
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