March 18, 2020
Sapphire Gemstones
At Blackacre we adore sapphires, they have superb qualities and naturally are found in an abundance of colours.
Sapphires are part of the mineral family corundum, with the chemical formula Al₂O₃, this family also includes ruby. On the mohs scale of hardness, sapphire comes in at a 7.5-8, making it a tough stone and therefore durable and highly suited for jewellery.
The colouring agents in blue sapphire are iron and titanium with the addition of vanadium in violet stones. Rubies contain chromium and in the case of brownish stones, iron is present as well. Different colours of sapphires contain varying trace elements which cause them to reflect certain wavelengths of light and hence exhibit a different colour.
Sapphires are found in a variety of places such as, Sri Lanka (formerly Ceylon), Thailand, Australia, Madagascar, Vietnam, Cambodia, and the USA. The most exquisite “royal blue” sapphires are found in Myanmar (Formerly Burma) and Kashmir, these are highly sought-after and treasured by many.
Rough sapphires grow in certain crystal systems due to the way that their chemical compounds fit together during the crystallization process. The diagram above shows the typical shapes that sapphires frown in whilst the image below shows rough yellow and blue sapphires exhibiting partially tapered bipyramidal crystal structures.
Rough sapphire crystals - The Natural Sapphire Co.
When looking to buy sapphires, many are confused by the terms “Natural” and “Treated”. A natural gemstone is one which has been taken straight out of the ground, cut and then sent to market. A treated gem is that which has been subjected to some form of clarity or colour enhancement, usually heat treatment, this by no means classifies them as synthetic gemstones. By heating sapphires, a weaker colour gem with visible “silk” (inclusions within the gem), becomes a much more vibrant tone with a better clarity.
Rutile needle inclusions in sapphires are often referred to as silk.
"Generally, inclusions make a stone less valuable. Price can drop substantially if the inclusions threaten the stone’s durability. Even so, inclusions can actually increase the value of some sapphires. Many of the most valuable Kashmir sapphires contain tiny inclusions that give them a velvety appearance. They scatter light, causing the coveted visual effect without negatively affecting the gem’s transparency." - GIA
Blue Sapphires
The most popular colour of sapphire, blues have been prized by royals and mere-mortals alike. The colour can vary from grey blue, pale blue, cornflower blue, royal blue, to deep blue-black. Mid-blue to rich royal blue tones are the most favoured of this colour of sapphire, with the finest historically found in Kashmir.
Kashmir sapphires are praised on their velvety appearance and rarely appear for sale, when they do, they can fetch extraordinary prices.
Padparadscha Sapphires
Meaning “Lotus Blossom” in Sanskrit, Padparadscha sapphires are a signature mixture of orange and pink which are extremely rare and highly collectable. It is debated what colour a Padparadscha sapphire should be, whether Salmon or Sunrise, however it is generally accepted that a light to medium pinkish-orange or orangey-pink is the correct tone.
Sri Lanka
Colour Change Sapphires
Sometimes known as Chameleon sapphires, this variety of corundum changes colour under different lights. Under daylight (fluorescent or LED daylight lamp), the stone will appear bluish-violet, whereas under incandescent lamps it will appear strong violetish purple to strong reddish purple. The colour change can be graded as light, medium or dark.
At Blackacre we source many of our sapphires from Sri Lanka, due to the artisinal and non mechanical mining methods used to extract the gemstones.
Take a look at our gem vault to see a selection of our sapphires and other gemstones available for bespoke creations.
