Guide to Gems: Illustrated Guide to the Identification, Properties and Use of Gemstones (Firefly Pocket)

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These richly coloured stones belong to the beryl group, which also includes aquamarine. Emerald's captivating green colour is unique and unparalleled in all other gemstones due to inclusions that make each stone unique. Along with high quality diamonds, blue sapphires and red rubies, the green emerald is one of the “big four”. Unlike the other three, however, emeralds are more fragile and exposure to excessive moisture should be avoided. High Value Semi-Precious Gemstones The cut (number of facets on the diamond) will affect the fire of the diamond, with cuts such as emerald cut having much less dispersion than a round brilliant cut diamond. The fewer the number of internal reflecting surfaces, the less dispersion takes place, and the less fire will be visible. Only discovered in 1967, supplies of this intense indigo stone are running out fast, and it has been predicted to run out within our generation.

Refraction occurs when light travels from the air into a denser material. As light passes from the air into the denser material of the gemstone, it is bent. The amount of bending depends upon the refractive index of the material. High refractive index materials bend the light more. Diamond has an RI of 2.42 and quartz an RI of 1.54. The higher the refractive index, the greater the dispersion, giving more fire. The bending of the light also leads to more internal reflection giving a greater degree of sparkle.The most famous gem of them all? Almost certainly, and all thanks to its remarkable fire, effortless brilliance and clarity to die for. Essential. When light falls onto a gemstone and is reflected within the gem, possibly several times, before exiting and being seen by you, the light hits the interior facets of the diamond at various angles. These internal reflections can lead to the colours being 'dispersed' or broken down into all the colours of the rainbow. Looking carefully at a diamond under bright light, you will almost certainly see a shimmering rainbow effect within the stone. That is the diamond's fire, and it is caused by the dispersion of the rays of light from the interior reflective surfaces of the gemstone. Did you know that glittering refers to the luster of the gold or the quality of the light that is reflected from its surface? The gleaming sheen of polished gold contrasts sharply with the dull luster of raw gold, which barely reflects when compared to its brilliant metallic luster. A mineral form of iron oxide, this stone is red when cut or powdered, and its name comes from the Greek for “blood”. Unlike other precious and semi-precious stones, hematite is opaque and does not diffract light. Its surface has a magnificent metallic shine and it can look similar to silver when polished. Sheila has used polished hematite stones in several pieces inspired by Orkney’s history such as her Ogham cufflinks, Runic torque bangle and magnificent Celtic penannular brooch. Onyx Some gemstones will change color when they’re viewed in different types of light. This happens because the gemstones absorb different wavelengths of light depending on the kind of light – such as sunlight and candlelight. Alexandrite looks a deep forest green in daylight but will often appear almost Ruby red by candlelight. Csarite® has a beautiful olive green hue in sunlight but shows flashes of pink and champagne under candlelight. There are varieties of Sapphire, Fluorite and Garnet that also change in this way – it is a phenomenal sight to see. Phosphorescence

Some gem species’ lusters may be referred to as ranges. For example, serpentines may have resinous, pearly, or waxy lusters. Sphalerites can range from resinous to even adamantine. In addition, some gemstone lusters have “sub-types.” These terms describe gems that are close to the main luster type. Sheila uses both precious and semi-precious stones throughout her jewellery designs, with each stone set-by-hand in our Orkney workshop. We carefully source gemstones for their quality and colour ensuring you receive the best quality stones. All of our gemstones are natural except for cubic zirconia, which are synthetic. Another beautiful stone known predominantly for its red variety, Spinel also comes in a beautiful array of dark purples, blues and pinks. An introduction explains geology, chemistry and gemstone properties in clear and accessible terms. Key aspects of gemstones are explained such as crystal structures and optical and physical properties.Gems with a greasy luster seem to have a layer of oil or fat on their surface. Examples of this luster include graphite and green serpentine. This is caused by a mass of microscopic inclusions within. Greasy luster is a characteristic feature of Garnets, Alexandrite, Peridot, Opals and certain Rubies. They can even feel greasy to the touch.