by Louise Schoneveld
Out of “the big 4” gemstones, we’ve already learnt about the two corundums; ruby and sapphire, now it’s time to go green with emerald.
Emeralds are a variation of the mineral beryl with the formula Be3Al2(SiO3)6. Pure beryl is colourless however trace amount of elements can cause beautiful colourations. Fe2+ within a beryl can make an aquamarine gemstone (fig 2.) while Fe3+ causes a golden variation known as “golden beryl” or “Heliodor” (fig 3.). The classic green colouration of emeralds are given by inclusions of chromium and occasionally vanadium.
Hardness and crystal habit:
On the Mohs scale of hardness emerald ranks a 7.5-8, which is harder than quartz, and equal with Topaz. Beryl usually grown as prismatic hexagonal crystals and can be striated lengthwise as displayed in fig 2.
Cheeky gemstone tricks:
As only the deep green beryl has a high value as an emerald, the light green variations are often heat treated to produce more valuable aquamarines. These gems are usually heated at between 400-450 C to ensure a beautiful blue.  This is much lower than the heat treatment required to improve sapphires.
Good quality emeralds range from US$7,500-$15,00 per carat
Good quality aquamarine are roughly US$200 per carat
Good quality beryls range from range from US$33 for colourless to US$171 for light green coloured per carat.
Where to find:
Sadly, you cannot find emeralds in Australia, not even in Emerald, QLD. The largest producers of emeralds are Colombia (80%) and Zambia.
The more you know about the gems you buy, the most interesting they are…