Ruby – the birthstone of July


We’re halfway through the year folks, when did that even happen?! The first half has been so much fun but it’s been speeding by for me and I feel like it really needs to slow down. So much to do / see / enjoy and so little time.

Anyway, let’s steer the focus back to the birthstone for this very summery month – the ruby. You July babes sure are lucky to have this fabulous gemstone as your birthstone!

July birthstone jewellery set with genuine feminine pink rubies and 14k gold fill chains and earwires. Made by Linda Sääv Jewellery.
Ruby jewellery set, the perfect set for a July born babe who likes a touch of feminine pink. All pieces made by Linda Sääv.

The feminine ruby

Rubies for me are the embodiment of femininity in a gemstone. Their hot pink to blood red colour is divine and are loved by women of all ages. Even someone who might not be that in to pink will still get intrigued by a ruby.

I mean if your jaw doesn’t drop from the sight of the ruby pictured below, you need to get your eyes checked!

Hot pink ruby wire wrapped in 14k rose gold fill, dainty and delicate jewellery at its best. Made by Linda Sääv Jewellery.
Hot pink and glowing little ruby wrapped in flattering 14k rose gold fill wire. Made by Linda Sääv.

Ruby science

The ruby is a pink to red variety of the mineral corundum (aluminium oxide, Al2O3) and is a sibling to the other corundum colour varieties named sapphires. In fact, all other gem-quality corundum stones not having a shade of pink or red is called sapphires (read on for the pink sapphire versus ruby debate).

A completely pure corundum is colourless, so rubies get their colour from trace amounts of chromium in the crystal lattice. The more chromium, the stronger the red colour. The chromium can also cause fluorescence, which adds to the glow and intensity of the red colour when viewed under ultraviolet light – even from the ultraviolet light in sunlight.

Colourless and Pink Ruby Crystals
Top left: colourless corundum crystal. Bottom left: irregularly shaped glowing pink ruby with a hint of orange. Right: raw ruby, loose and in host rock with a hint of purple. The faceted ruby is more red with a hint of pink.

Iron can also be present in the chemical makeup of a ruby. Iron on the other hand can make the rubies darker and less intense in colour. Higher iron content can also mask the red fluorescence.

50 shades of red

Although rubies are defined to be red, they may exhibit a range of secondary hues, including orange, purple, violet and pink (as already seen in the previous photo). Of the three, purple is preferred because it reinforces the red, making it appear richer. However, too much purple and the ruby moves down the quality scale.

50 shades of red
50 shades of red. Nah, just kidding, sort of. Even though it might not look like it, all rubies are defined to be red in hue. The pink or purple colouration you see is only caused by their secondary hues.

The ruby hex

Rubies (as all corundum varieties) are part of the trigonal crystal system and most often occur naturally as terminated tabular hexagonal prisms. Imagine two stretched six-sided pyramids attached at their base and you have a rough idea of how a ruby crystal looks like.

Natural Hexagonal Ruby Crystals
Top left: raw ruby crystal showing off its hexagonal shape, it’s also showing off that it’s part of the trigonal system with the triangle on its top. Right: a raw ruby with a faint hexagonal shape. Bottom left: a collection of ruby crystals and clusters (and one blue sapphire).

Rubies are naturally very hard with a hardness of 9 on the Mohs scale of mineral hardness. Only moissanite and diamond are harder, with diamond having a hardness of 10 and moissanite falling somewhere in between corundum and diamond.

Naturally imperfect

When it comes to imperfections, all natural rubies have them. Imperfections include colour impurities and inclusions of rutile needles known as “silk”. It’s the rutile inclusions that make distinguishing natural rubies from synthetics or simulants possible.

Rutile Needle Inclusions in Rubies aka Silk
Left: rutile needles (golden) on hematite (metallic). Top right: microscope image of a criss cross pattern made by rutile needles in a ruby. Bottom right: Close up of thin rutile needles making the same but faint criss cross pattern seen above.

The rutile inclusions can sometimes cause an optical phenomenon called asterism. An asterism or “star” is a three-point or six-point surface effect that occur when light is reflected off the structurally oriented rutile needle inclusions of the stone in a certain way. These rubies are usually cut into cabochons to properly display the effect. Similarly, rubies can also show chatoyancy, also called the “cat’s eye” effect. In this case, the rutile needle inclusions are actually increasing the value of the ruby.

Asterism in Rubies Caused by Silk
Two cabochon cut star rubies clearly showing the six-pointed surface effect caused by the silk within.

These days, almost all rubies are treated in some form, with heat treatment being the most common practice. Heat treatment of a ruby improves the colour, removes any purple tinge as well as “silk” which also improves the clarity.

Another treatment is lead glass filling, a treatment where any fractures inside the ruby is filled with lead glass, a treatment that dramatically improves the transparency of the stone.

Untreated versus Treated Rubies
Untreated rough rubies (left) versus heat treated rough rubies (right).

Ruby vs. pink sapphire

The distinction between ruby and pink sapphire is often made by looking at the colour saturation of the stone. If the saturation isn’t high enough it will be called a pink sapphire and subsequently, if the saturation is above a specific threshold it will be called a ruby. Furthermore, one can argue that for a corundum to be called a ruby, red must be the dominant hue.

However, often, the identification of the dominant hue is difficult and can be debated – it’s not clear and it really is just a matter of personal perception.

Historically though, the word ruby referred to shades of red, which technically included pink.

Rubies with same hue but different saturation and tone
Four different corundums having the same hue (red), but showing a variation in saturation and tone. Most gem dealers would classify number 3 and 4 as rubies, whereas number 1 would be classified as a pink sapphire. Number 2 walks the line, it’s a ruby to some, while a pink sapphire to others.

The queen of gems

Ruby is the most valuable variety of the corundum mineral species and rubies can in fact command the highest per-carat price of any coloured gemstone.

The quality of a ruby is determined by the same principles as other precious gemstones: colour, cut, clarity and carat weight – all of which affects its value.

For rubies, colour is the most important quality factor. The finest ruby has a pure, vibrant red to slightly purplish red colour –  called “pigeon’s blood” rubies. After colour follows clarity: a clear stone will naturally be more valuable. However, a ruby without any needle-like rutile inclusions may indicate that the stone has been treated, which lowers its value.

Rubies in the wild

Rubies are most often found in marble. The most renowned rubies, like those from Myanmar, the Himalayas and northern Vietnam, typically form in marble.

Here they’re found in layers that are distributed irregularly within the surrounding marble. The marble is formed from existing limestone deposits during metamorphic (rock-altering) processes.

Marble is a type of rock with low iron content, which means rubies formed in marble are more likely to have an intense red colour due to the lack of iron.

Rubies in Dolomite Matrix
Rubies in marble showing off their more vivid colouration.

Rubies can also be found in basalt rocks. Basalt has high iron content which means that rubies originating in these rocks can have higher iron content as well. And as you’ve already read, the addition of iron can cause the rubies to be darker and less intense in colour (see picture below), as well as mask the red fluorescence, eliminating that extra glow of red colour seen in rubies originating from marbles.

Another type of ruby is found in amphibolite and the most renowned ones originate from Mozambique. These rubies are quite fascinating due to their range in iron content, from as high as rubies found in basalts to as low as rubies found in marbles. This of course causes a wide range of colours for rubies mined in this area.

Rubies in Amphibolite and Ruby Colour Difference Due to Iron Content
Top left: rubies in amphibolite. Right: rubies with high iron content.Bottom left: rubies with low  iron content.

So which ruby is your favourite? The more red ones or the more pink ones? I for one is a sucker for those hot pink fuchsia coloured ones!

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I hope this blog post was interesting and fun to read and that you now have a little better understanding and appreciation of this beautiful queen of a gemstone!

I’ll be back in a couple of weeks with something completely different, so until then, have a wonderful time wherever you are!

♥ Linda