Beryl

Beryl is one of the oldest known minerals, and offers a rich mix of gemstones including emerald, aquamarine and morganite. Containing beryllium, an element named after the mineral by French chemist Vauquelin when discovered in 1798, it's a sought after gemstone often priced depending on the intensity of the individual colours. This, however, has resulted in a lot of contemporary beryl stones being heat treated in order to increase their colouring. 

 

Emerald

The most valued beryl variety is emerald, which may sometimes fetch even greater prices than certain diamonds. The name derives from ancient an Persian word that appeared later in Greek as smaragdos, which in turn gave rise, via Latin, to the Old French esmaraude, Middle English emaraude and, finally, to emerald. It is the chromium and vanadium present in the emerald which produces it characteristic vibrant colour. The colour of emeralds varies according to its source, the most desirable colour being a strong, slightly bluish green. Very few emeralds are absolutely 'clean.' They often have inclusions of fibres or tremolite rods, internal cracks or irregular colour distribution, and can appear cloudy or 'sleepy.' The resulting internal stresses make emeralds very sensitive to pressure. As a response to that, the emerald cut was specifically designed to maximise the valuable stone and to intensify its colour. This cut, in which the corners are removed to avoid chipping or breaking, also protects the somewhat brittle material. 

Emerald Ring
 

Aquamarine

Aquamarine can be found in sea green, sky blue and dark blue. in the 19th and early 20th centuries, sea green was preferred leading to the gem's named which is derived from the Latin aqua (water) and marina (of the sea). However, since then sky blue and dark blue have become more desirable and the most valuable colours. Aquamarine is dichroic, meaning the intensity of the colour changes depending on the angle it is viewed from. Because of this the material is usually cut according to the best colour angle as opposed to greatest size, the step cut or emerald cut frequently used. Aquamarine has a higher level of clarity than its greener emerald counterpart. It is far easier to find clean stones at a good size, and fewer inclusions and cracks mean that there is less internal stress and the material is less brittle. Flawed material that is cloudy and nearly opaque does exist, but is normally used for beads and cabochons, where it can sometimes produce a cat's-eye effect.

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Natural Aquamarine
 

Morganite

Coloured by manganese impurities, morganite can appear as pale pink, rose pink, peach, apricot, salmon and even violent in colour depending on the concentration of the element. The majority of morganite has a soft peachy pink colour that can be made more intense by using a closed setting of white metal. The first morganite stone was discovered in California, alongside the equally stunning tourmaline. Like aquamarine and emerald, it is dichroic and shows two shades of colour when viewed along different axes. 

Morganite stone

Sources:
Judith Crowe, The Jeweller's Directory of Gemstones (London: A&C Black, 2006)
Cally Hall, Gemstones (London: Dorling Kindersley, 1994)
Jaroslaw Bauer and Vladimir Bouska, A Guide in Colour to Precious & Semiprecious Stones (London: Octopus Books, 1983)