When we talk about gemstones, you may be familiar with the terms precious and semi-precious stones. There are only four precious stones – diamond, ruby, sapphire and emerald – and all other gemstones are known as semi-precious. 

Most people are familiar with diamonds, but how well do you know the other three gems? Here, I have put together some information on the technical aspects of rubies, sapphires and emeralds.

Physical and chemical properties

Both rubies and sapphires are varieties of the corundum family of gemstones, meaning they are dense and compact, and are the second hardest natural mineral, with diamonds being the hardest. They also both have no gemstone cleavage, which means they lack planes in the crystalline structure with weak atomic bonds, making them hard to split.

Emeralds are a variety of the beryl family of gemstones and are not quite as hard as rubies or sapphires, but they are still very solid and have an indistinct gemstone cleavage. All three stones have a hexagonal crystal structure.

Corundum is formed of aluminium oxide, with traces of chromium and iron in rubies, and traces of iron, titanium, chromium, and other elements present in sapphires. Beryl is formed from beryllium aluminium cyclosilicate with traces of chromium and vanadium.

Clarity

The clarity of gemstones is determined by qualities such as transparency, blemishes, and inclusions. Whilst high clarity is often a priority for many, inclusions (especially in emeralds and sapphires) can be part of their charm. Emeralds, for example, often feature long hollow tubes as part of their structure and may not devalue the gem. In the case of Kashmir sapphires, fine silk inclusions scatter light and give the gem a soft appearance.

What gives these gems their distinctive colour?

Gem-quality red corundum are all rubies, and any other gem-quality colour variations are sapphires, which we traditionally associate with a deep blue colour, though they do come in greens, pinks, yellows, and more. Rubies get their distinctive colour from the levels of chromium and iron in their makeup which can manifest as a range of red hues, from pink or purplish to orange or brown.

Trace elements of iron, titanium, chromium and vanadium, among others, can give sapphires their wide spectrum of colours. Emeralds get their dazzling green variations from their chromium and vanadium content, and iron content will provide bluish tones. Both sapphires and emeralds are uniaxial gems, meaning they can display two colours when viewed from different angles.

Value

In general, the value of most gemstones will increase the bigger they are, provided they are of high quality. However, due to the rarity of small, gem-quality rubies, these will often fetch a high price.

The place of origin and colour affect the value of a ruby and custom cut or recut rubies are often worth more due to their rarity. The main determiner of a sapphire’s value is its colour, and whilst they come in a range of colours, the traditional pure blue with vivid saturation is the most valuable. Like sapphires, the colour, hue, and saturation will mainly determine the value of an emerald, with a strong bluish green fetching the highest prices.

What are they used for?

Each of these precious stones make for great pieces of jewellery in both simplistic and more ornate designs. Individual taste will always be a factor and certain stones will have personal meaning for some. 

Rubies, sapphires and emeralds also have significance for certain events. Ruby is the birthstone for July and also the gemstone for a 40th wedding anniversary. Sapphire is the birthstone for September and the gemstone for a 45th wedding anniversary. Emerald is the birthstone for May and is also the 55th wedding anniversary stone. Jewellery containing the corresponding stone makes a great gift for any of these occasions.

When it comes to comparing rubies, sapphires and emeralds, personal taste will almost always be the deciding factor, but hopefully you are now a little more informed on the specifics that make these precious stones so unique.

If you were also interested in learning about diamonds, you can read our blog on the 5 Cs of diamonds.

Here at Milina London, we offer a bespoke jewellery service to tailor jewellery exactly to your requirements. We create with precious metals such as sterling silver, gold or platinum, and can source precious gemstones including rubies, emeralds and sapphires to make your piece.

We can also repurpose an existing gemstone or piece of jewellery into something more modern, so that you can wear it while treasuring the sentimental value.