Emerald

Composition and Characteristics

The name ‘emerald’ was not used in England until the 16th century and has its roots in Latin, ‘smaragdus’, and the later mediaeval; ‘esmerande’, ‘emerande’ and ‘esmeralde’. All of these names refer to the deep green colour of the stone.

An emerald is a member of a range of stones called Beryl (Be3Al2 (SiO3)6) by mineralogist. The colour spectrum for Beryl is broad and includes Aquamarines in shades of blue-grey, morganite in pink and yellow heliodor. The purest form of Beryllium is colourless. The rich green colour characteristic of emerald is created by the presence of other mineral deposits within the stone, such as traces of chromium or, less frequently, vanadium. Although, these additional minerals are technically impurities in the beryllium, they create the bright colours that make the stones so attractive and valuable.

Fragility

Emeralds are the most fragile of precious stones, although, they score 7.5-8 out of 10 on the Mohs they are susceptible to cracking if knocked against a hard surface due to their brittleness.

This brittleness is created by impurities within their matrix, which give the stones large numbers of inclusions. Despite this fragility, emeralds are still much desired for their deep and vibrant colour which has made them a favourite of the world’s elite for millennia.

The Emerald Cut

The rectangular cut commonly used for emerald’s is not entirely a preference of style, but a requirement of the stone’s composition as the emerald’s brittleness makes it difficult to cut and facet with complex patterns like a diamond. The commonest cut for emeralds has been named after the stone; the step, ‘emerald’ cut uses few facets so the simple, long and linear facets do not create brilliance like a diamond (link diamonds), instead the long cuts showcase the deep colour of the stone.

Cedar Oil Infusions

Today most emeralds have been treated with cedar oil infusions to disguise the natural inclusions. These inclusions could be a combination of internal hairline fissures, air bubbles or bits of other minerals. Such inclusions are commonly referred to as the ‘jardin’ (garden) of the emerald by trained gemologist’s who can read the unique composition to discover the national origin of the gemstone. Cedar oil infusions is a common, and long practiced, form of emerald treatment accepted by jewellers and gemologists, unlike synthetic oil or polymers like Opticon which artificially intensify the colour of the stones.