Beryl is a beryllium-aluminium silicate, with its non-gem material mined for its beryllium content. It’s a very light metal with a high melting point and elasticity, which is used in industry alloyed with other metals. Pure beryl is colourless, but most gem quality material is transparent and coloured by a variety of trace element impurities creating a range of lovely hues.
Part 1 analysed the emerald, the popular beryl gemstone that radiates a verdant green colour, however, there are also paler green tones, which are simply named green beryl. Beryl’s brilliance is best shown with an emerald cut, so green beryl needs to be cut as deep stones to show depth of colour. Luckily, unlike emeralds, green beryl and other paler colours can come in large crystals with few inclusions.
The colour of aquamarine beryl (named from the Latin aqua marina, meaning sea water) is greenish-blue to blue-green (dichroic or showing 2 colours), caused by impurities of iron oxide. Most aquamarines are heat treated to remove green tinges because blue hues are considered more fashionable. It can be confused with blue topaz. Aquamarine is usually cited as the birthstone for March. It makes wonderful cocktail rings due to the large cuts!
Pink beryl is known as morganite, named after the American financier and gem collector J. P. Morgan. Its colours include pink, rose, peach and salmon, which are due to traces of manganese. It is often heated to burn off the salmon colours to allow for more ‘in vogue’ pink tones. Like aquamarine, the crystals can be quite large, free of inclusions and pale, so larger faceted gems are fashioned to give the depth of colour preferred.
Morganite is dichroic, showing two distinct colours, a pale pink and a darker bluish pink, when viewed in different directions. It must be cut very carefully to obtain the best colour. Morganite can resemble pink topaz, pale pink spinel and pale pink sapphire.
The colour of heliodor beryl varies from pale lemon to rich gold. Its name comes from the Greek meaning for Sun (helios) and gift (doron). It is an inexpensive beryl that can be mistaken for citrine, but it is not frequently used in jewellery due to higher popularity in other beryl gemstones.
The colourless goshenite is probably the least known beryl. It was named after Goshen, a place in Massachusetts where it was first discovered. It makes for a lovely stone when cut, and it has been used to imitate more precious gemstones such as diamond.
Beryl is found mainly in pegmatites (notable exceptions are emeralds in mica schist in the Ural Mountains and limestones in Columbia) and in a variety of localities around the world. All beryls have a hardness of around 7.5 on Moh’s scale, sufficiently hard for everyday wear. They all tend to brittleness, so must be cut very carefully, both to minimise the chance of accidental fracturing and to obtain the best depth of colour. Beryl are all dichroic and are often heat treated to make the colour purer. The brilliance and colours of well-cut beryl make it one of the most versatile gem families.
More reading
Colour investigation: Beryl (Part 1)