Ruby, The Pigeon Blood Stone of the Gods.

Corundum ruby, 17.30 g, crystal in calcite, collection# 24187, from Kyauksaung, Myanmar. Gift of William F. Larson. Left to right: Collection #33066, oval cut ruby, 1.77 ct, from Myanmar; Collection# 33065 cushion cut ruby, 2.21 ct, from Myanmar; oval cut ruby, 6.32 ct, from Burma, courtesy of Edward Boehm.
Corundum ruby, 17.30 g, crystal in calcite, collection# 24187, from Kyauksaung, Myanmar. Gift of William F. Larson. Left to right: Collection #33066, oval cut ruby, 1.77 ct, from Myanmar; Collection# 33065 cushion cut ruby, 2.21 ct, from Myanmar; oval cut ruby, 6.32 ct, from Burma, courtesy of Edward Boehm.

I find these blogs just keep getting longer and longer as I add more and more information each month. But, that’s what I love about this, being able to share what I know from the world of gemmology.

July, a hot month for a burning hot stone, figuratively of course. Ruby is known to be the traditional birthstone for July and is the vivid, glowing red variety of the mineral corundum. Rubies are an ancient stone and carry many meanings attached to them, but generally are associated with the sun and blood, thus they symbolize nobility, purity, passion and life. Rubies have a long history, with mentions from the bible and from ancient India. They are especially revered in South-East Asia and India and used to adorn all forms of ornaments and clothes of the royalty of the area. While today there are many locations where rubies have been found and mined, Burma now Myanmar, has been the source of the most desired rubies from as far back as 600CE. It was here the optimal colour, pigeon blood red, was sourced. In days past, a perfect ruby was the colour of fresh pigeon blood on white sheets, morbid but also kind heavy-metal, no? These prized stones hail from the Mogok area of Myanmar (Burma) and while Mozambique and Sri Lanka are also hosts of beautiful rubies, the Burmese name will cost you more. Think of it as buying a brand name for shoes or clothes over no-name, Burmese rubies are like the Gucci, Dior and Prada of rubies.

Natural, untreated pigeon-blood ruby of Mogok, Myanmar.

Ruby is identified as:

  • 1) Trigonal Crystal System, not to be confused with crystal habit. (Note, habit is how the mineral crystallizes)
  • 2) Oxide Composition, 
  • 3) Simple Oxide Family
  • 4) Mineral = Corundum – Al2O3
  • 5) Variety = Ruby.   

Like beryl, corundum is naturally colourless, and thus colour comes from impurities within the stone. Ruby is the red-crimson variety, sapphire is the blue variety and padparadscha is the pink/orange variety. All other colours are classified as “fancy sapphire”, this is odd as the beryl varieties had unique names but when it comes to corundum in the yellow, violet or green hues then they are referred to as a “yellow sapphire”, “green sapphire”and “violet sapphire”. Confusing, I know, even to a gemmologist. Unless a colour is in front of the word “sapphire” then it is assumed one is referring to the blue variety of corundum.   

The man colours of corundum. Blue sapphire and sapphire alone refer to the same colour.

Now for the fun part, how is ruby so red? Ruby, (derived from ruber; Latin for “red”, big surprise there) gets its colour from traces of chromium, within the crystal structure. Remember our blog from May and June, chromium is a very colouful element. Green in emeralds and colour change in alexandrite. This element does more than just give you a shine on your wheels. As started before this colour all comes down to how light interacts with chromium ions, chromium(III) to be specific, within the crystal lattice. Without getting too technical, when chromium is in corundum it will replace an aluminum ion and the distortion causes the chromium electrons to absorb the ultraviolet, violet, and yellow-green regions of the spectrum. If one percent of the aluminum ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem. With emeralds, the chromium absorbs more of the violet and yellow-red wavelengths of visible light, thus we see green. 

Now, let’s get serious about rubies.  With the high price of rubies, some exceeding far beyond the cost of diamonds even, there are many treatments, synthetics and imitations to watch out for when hunting for rubies. First, some terminology needs to be explained, mainly the terms “natural”, “synthetic”, “imitation” and “treatment”. A natural gemstone refers to a stone made from the earth and is what most people desire/expect. A synthetic gemstone is an identical copy of a natural, just made by man. This means it has the same chemical formula and crystal structure as its natural counterpart. Ideally, the term “synthetic” should only be used if the man-made stone has a natural counterpart. If there is no counterpart, then this stone is referred to as an “imitation”. An imitation is a stone or material representing another stone. Imitations can be natural or synthetic and confuse many people. Cubic zirconia is one of the most common samples for imitating precious stones. Treatment or a treated stone is a natural stone that has been tampered by humans to improve colour saturation, clarity, and durability. There are many interesting ways we have discovered to help improve the natural beauty of precious stones. 

For rubies, the most common treatment you will see is heating and assembled rubies. Heat treatment is as the name suggests. The rubies are slowly heated up to a temperature of 1800 °C. The heat helps eliminate inclusions and can enhance the colour of the stone. An assembled ruby is actually ruby grains assembled with leaded glass and coloured with a variety of elements, like copper, boron, sodium, calcium or potassium. This is a 4 step process and commonly used to fill fractures within the ruby. Oiling is another treatment used on rubies but not as common as with emeralds. The stone is placed in heated oil in a vacuum chamber and the oil is then drawn into the cracks of the stone or it is ground while the stone is being cut. All of the treatments are used to help increase the clarity and colour of the ruby as a clear and vibrate stone is the most desired. 

Before and after glass-filled ruby treatment.

Now for the best part, how can one tell if their ruby was treated, synthetic, imitation or a natural red wonder? Well the most obvious answer is get a professional to look at it. Second, like with all gemstones look at the cost. If the price is too good to be true then it probably is. Sometimes traders don’t know their material and this can work in your favour or against you, buyer beware. If you have a loupe or a strong magnifying glass there are a few things you can look for in your ruby. For the assembled or glass filled rubies the difference in lustre between the glass and the ruby can help in identification. With a loupe, looking at the light reflected off of your ruby, examine for cracks and fractures, if you see a difference in lustre, or shine, the duller material is the glass and the brighter material is your ruby. You may also see bubbles in your filled fractures from the glass. 

Microscopic view into an assembled (glass-filled) ruby. Air bubbles within the glass gives it away as round bubbled never form within natural minerals.

For heat treatments you need a microscope but if you happen to see inclusions in your ruby, especially other minerals look at the crystal surrounding the inclusion. If you see cracks or minor fractures radiating out from an inclusion, like a lily pad, that is possible evidence of heat treatment. The heat caused the inclusion to expand and contract at a different rate compared to the rest of the ruby, thus stressing the ruby and causing it to crack. You may also see “healed” fractures but alas you will need a professional eye to show you what I’m referring too. Oiling is fairly easy to identify as your hand/fingers may become red after handling the stone. You will also notice with your loupe that the colour of the stone is concentrated along fractures within the crystal.  

Flux-melt ruby to the left and flame-fusion boule to the left. The cut stones are faceted examples of each.

Now what about natural vs synthetic rubies. A flawless gem is the most prized gem but also one of the most difficult to identify as inclusions help greatly. When it comes to synthetic stones, you’ll need a microscope to discern the origin of your ruby. All gemstones leave clues as to how they formed within the crystal structure and carry trace element signatures. While the chemical signature is the best way to identify a stone’s origin you have to destroy a piece of your stone. I don’t think many people would be interested in having a hole in their $30,000 ruby to see if it’s natural or synthetic. Thus by using high powered microscopes and polarized light, gemmologists can see signatures as to how gemstones crystallized and your stone is left untouched. Synthetic rubies are produced either through the flux-melt method or flame fusion method. These methods should be disclosed when selling synthetic/lab-created rubies and if not, ask. Since I will be talking about sapphires in September, I will focus on the flame-fusion process here and the flux-melt there.   

A diagram showing how flame-fusion corundum is made. This process was made possible by the French Chemist Verneuil. The hammer vibrates the powered at a controlled rate which then drops and melts onto a growing, rotating synthetic ruby.

The most common synthetic ruby is the flame-fusion ruby, a process improved upon by the french chemist Auguste Victor Louis Verneuil to start producing synthetic ruby and sapphire in mass quantities. In a nutshell, the stone is grown like a stalactite, from the base up. Aluminum oxide (corundum) powder and chromium oxide (red colour) are mixed together and then sprinkled at a controlled rate through an oxyhydrogen flame and heated to 2200℃. The now liquid droplets of ruby then fall onto a seed crystal and the ruby begins to grow. The end result is a ruby or sapphire boule. The reason this process is so popular is because the crystals grow at an alarming rate. A typical 40 by 80mm boule weighing 250-500 carats would take 4 hours to create. This process works for creating synthetic spinel as well. Little fun fact here, while you can create ANY colour of sapphire, chemists are still unable to create an emerald green sapphire. Today the yearly, world production of flame fusion corundum due to Verneuil work totals over 1 billion carats, most used in watches, lenses and manufacturing.  

Two distinguishing featured found within the flame-fusion ruby. The curved striae are visible in the background and the cylindrical bubbles in the center.

The rubies created by the flame-fusion process are grown, layer by layer. These layers are actually curved called “curved striae” and a distinguishing feature of the ruby as each layer is built upon the last layer and oozing over it, like a tower of pancakes. Now a hard fact here. Nothing in natural minerals is curved when you’re referring to the growth of a mineral (fractures are the exception but that’s for another time). Now these curves are usually only visible with a microscope unless it was a rushed crystal. Other features would be inclusions of bubbles or unmelted powder sprinkled within the ruby. 

How pleochroism is expressed in a natural vs flame-fusion ruby. Also how gem cutters maximize carat from each crystal.

Another way to tell these synthetics from naturals is if you look through the table of your stone with a dichroscope or using a polarized lens/glasses. If you see your stone strongly change colours as you rotate it with light from behind, you may have a synthetic. Reason for this is because of the structure of the boule. While ruby and sapphires are hard, they can be brittle, and when you’re grown in an unnatural way, you’re going to be unnaturally brittle. To prevent this, split the boule down the middle once it’s done crystallizing. This releases the tension built up in the curves layers. The changing colour comes from a property all crystals have, well all but the cubic crystal system (they’re special), called pleochroism. In short this means the atomic structure of crystals can split light into two waves, the short and long wave, due to the duality nature of light as an elector-magnetic wave/particle. In turn you will see some stones change colour depending on the angle of the stone to your eye. Ruby, being a trigonal stone, has this property and when viewed from the side as opposed to down the “optic axis” (the angle at which both light rays are at the same speed and thus don’t split). I know there’s a lot here but add this all up together knowing the fact that the boules grow along the optic axis as well. Thus when you split the boule, your largest surface is now the split side. Gem cutters then use this side as the table face to save carats. This face is perpendicular to the optic axis thus pleochroism is as its highest value, ot more noticeable. SCIENCE AND LIGHT!!!

Looking at a ruby with a dichroscope perpendicular to the optic axis. This is what you will see if you are looking directly at the face of a flame-fusion ruby.

Now if you want to search for your own ruby, just like all the other precious stones out there, it is a buyer beware world out there. Ask questions, and use your gut first. Also look at the name. Many stones have the name “ruby” in them in order to make you think they are related. The infamous Balas Ruby in the Royal British Crown is actually a red spinel. Rubellite is a pink/red variety of the tourmaline family. Again if it’s synthetic, the process should be indicated with the purchase. Imitation stones will be easier to spot as they will not be as hard or will not show the pleochroism. 

Star ruby displaying natural growth rings. A true wonder of light and colour.

What about star rubies? Yes they exist naturally and are the result of thin mineral hairs of rutile crystallizes alongside the triangular habit/system of the mineral. When these hairs are cut into a dome or cabochon shape along with the rest of the ruby, the hairs will reflect light like a spool of thread. With three spools comes three reflections thus we see a star. This is a phenomenon known as asterism, and if there is only one reflection like a slit, it’s known as chatoyancy, or ‘cat’s eye’.      

While these are just some quick pointers for general interest if you are interested in more information I suggest some of the links and books below.

Wikipedia, though not officially credible, it’s a great place to start. Also look at the reference they use.

GIA encyclopedia page for rubies. Very friendly for just starting to understand gemstones with links to countless articles about ruby mines, unique specimens, ruby history, lore and more.

Gemmology by Peter read – A gemmologist bible, make sure to look for the latest addition as there is always new information to be added to textbooks. This book covers ALL the gemstones as well as how to use the tools to identify naturals, synthetics and imitations. Warning this book is very technical. 

Jewels: a secret history by Victoria Finlay – an excellent read into the history and lore behind some of the more renowned gemstones.  

Well that was a novel and a half, I hope you enjoyed this blog about the July stone, Ruby. In August I will be informing you about Peridot, the olive-lime green gemstone of the deep earth.