Bi-Coloured Gemstones

Bi-Coloured Gemstones

Written by Tom Wilson on 6 October 2012

Since starting at Harriet Kelsall Bespoke Jewellery, I have learnt so much about bespoke engagement rings, one of my favourite aspects of my job is seeing the extensive variety of gemstone engagement rings being commissioned. I am particularly fascinated by bi coloured stones. One of my personal favourite examples of a bi coloured gemstone is the watermelon tourmaline. Watermelon tourmaline is an unusual looking stone; the colouring resembles the pink flesh and green rind of a watermelon.

Watermelon Tourmaline Engagement Ring

Tourmalines aren’t a single type of mineral but are actually a closely related group of minerals, which is why tourmalines can come in a wide variety of colours, and the possibility of bi coloured stones, tourmalines can have two or more colours within the same crystal.

The colours of watermelon tourmaline can vary from a deep rich green to a clear pastel tone; similarly the pink area of the stone can vary from a subtle baby pink through to a vivid fuchsia pink. The colour balance within the stone often preferred to be approximately equal amounts, however stones with an uneven colour fade can also be extremely beautiful and would be stunning in a bespoke engagement ring.

Due to the nature of tourmalines, other bi coloured stones that can be found are: blue to green fades, these can range from a deep blue to a stunning teal colour fading through to a wide range of greens. If you love the colour pink, more than one shade can be seen within tourmalines, starting with a bright hot pink at one end of the stone to a pastel. Yellow green combinations can also be found. Tourmaline is believed to strengthen the body and spirit, and protect the wearer against dangers and misfortune. Watermelon tourmaline balances the male/female energies and is useful for attracting love. It is also thought to enhance inspiration and encourage self confidence.

Another type of bi coloured stone is ametrine, this is a combination of amethyst and citrine both of which are members of the quartz family. The colours of natural ametrine are produced by iron impurities within the quartz. Due to the colour variation being natural, no two ametrines will ever be exactly alike, which for a bespoke engagement ring would be a brilliant feature.
The purple and golden colours are a result of different oxidation states of iron impurities. Very specific conditions have to be present In order for the iron within the stone to oxidise correctly to produce both colours within the same crystal. Not only does one area of the stone have to be exposed to more heat, while another section is slightly cooler; the dual temperature condition has to remain stable during the entire growth cycle of the crystal. However some purple golden ametrines can be produced in a laboratory by heat treating natural amethyst to alter the oxidation state of the iron in parts of the rough crystal. Ametrine is said to stimulate the intellect.

Bicoloured stones are often found in baguette or emerald cuts, so that the colour fade can be shown and appreciated to full advantage. If you can’t decide on just one colour for your engagement ring, why not choose a bi coloured stone?