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.

Cut gemstones of Emerald Image from - http://www.capitolcraftsman.com/
Cut gemstones of Emerald Image from – http://www.capitolcraftsman.com/
Colouration:

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.

http://www.vietrocks.com/aquamarine.html
Fig 2. Aquamarine variation of Beryl. Image from http://www.vietrocks.com/
http://www.gemstonebuzz.com/
Fig 3. Heliodor gem Image from http://www.gemstonebuzz.com/
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. [1] This is much lower than the heat treatment required to improve sapphires.

Prices!

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…


[1] http://gemologyproject.com/wiki/index.php?title=Heat_Treatment