What is a Sapphire?

For those curious as to the science and the gemmology of sapphire this article is a great guide.

What is in it?

Sapphire is a gemstone that is mainly composed of corundum along with; iron, titanium, chromium and copper. All of which are minerals. If you see sapphire that is of a blue, yellow, purple, orange or even a greenish colour, minerals such as iron, titanium, chromium copper and/or magnesium give the corundum that colour.

What is Corundum?

Corundum is a crystalline[1] form of aluminium oxide. The crystalline has traces of other minerals such as iron, titanium and chromium[2]. In its most natural state, the mineral is transparent. This does not remain true because the corundum can actually shift colours when tainted. The transparent minerals are used as gems and are called ruby if they give a red glow and padparadscha[3] if given a colour of pink-orange. All other corundum that projects any other colour are labelled as sapphire.

There are two dominant ways in which corundum is formed. One is the metamorphosis[4] of limestone and the other involves the igneous occurrence in rocks lacking silica[5].

Corundum is rated as a 9.0 out of ten in terms of the Mohs scale of mineral hardness.

What is Aluminium Oxide?

Aluminium Oxide consists of the compounds oxygen and aluminium (Al2O3). Alpha-Al2O3 or corundum is the most commonly known and significant modifications of aluminium oxide.

Aluminium oxide is produced by machine from the mineral bauxite. There are currently 20 billion tons of bauxite deposits in the world. Aluminium and aluminium oxide are manufactured by the principles of the Bayer method: Bauxite[6] is broken and dried and is then dissolved using concentrated sodium hydroxide soloution. The left overs (iron, silicon and titanium) are segregated from the bauxite in the red mud. The aluminium hydroxide is then precipitated from the mix and then calcinated[7] at 200-1300°C to form Al2O3.

How are Sapphires Cut?

Sapphires are very rare gems. You will often see sapphire presented as jewellery in the shape of either an oval or a cushion. Ovals and cushion tend to preserve most of the original rough. Round sapphires are popular as well, however their final shape involves removing a large portion of rough and are as a result are costlier than ovals and cushions.

Sapphires are treated by several methods so that the quality of the gem and colour are enhanced. One technique of doing this is by heating. This type of treatment is done in furnaces between 500-1800 degrees Celsius for hours at a time. By heating the sapphire, the colour of the gem becomes more blue. As well the stone becomes more clear because it loses silk and it becomes clearer under magnification. This is just one of other techniques used to treat sapphire.

Where is Sapphire Mined?

Sapphires are found in igneous[8] and metamorphic rocks. When sapphires are extracted from solid host rock they are labelled as primary deposits. They are considered as secondary deposits when they are found some distance from their original source. Rocks are hit against by water and wind. The process of erosion moves small pieces of rocks into streams of water where they are broken, releasing any gems that they contain.

Word Search


[1] Pertaining to crystals or their formation.

[2] A lustrous, hard, brittle, metallic element used in alloy steels for hardness and corrosion resistance.

[3] A delicate light to medium toned pink-orange to orange-pink hue corundum.

[4] Any complete change in appearance, character, circumstances, etc.

[5] The dioxide form of silicon.

[6] An amorphous clayey rock that is the chief commercial ore of aluminum.

[7] To convert into calx (the oxide or ashy substance that remains after metals, minerals, etc., have been thoroughly roasted or burned) by heating or burning.

[8] Geology . produced under conditions involving intense heat, as rocks of volcanic origin or rocks crystallized from molten magma.



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What’s in A Ruby?

Prior to investigating the best way to purchase a natural ruby stone, I was under the impression that natural unadulterated rubies would be expensive but relatively easy to find.   To my surprise, it is very difficult to find a completely natural untreated ruby gemstone with few to little inclusions.

Unfortunately, it is still common practice for many vendors to lead consumers to believe that they are paying a premium to purchase an untouched natural stone for their jewellery. In fact most of the time, those very stones have undergone some form of treatment.  This practice in some cases is not intentional on the part of vendors, since they also have been lead to believe that the stones they are selling natural.  It takes special equipment that certified gemologists use to conclude the level of treatment if any that gems have undergone.  So, why does this matter to the client since treated stones can be just as beautiful as or more so than an original stone?  It has to do with clients simply understanding the product they have purchased.  For example if a consumer believes that the stone they purchased is untouched, and flawless, they would presume that to be the measure for which the stone holds a certain value.

One method rubies and many other gemstones are treated is by fusing the gems with glass.  This effect can provide additional lustre to the ruby. One should be aware, however that there may actually be more glass component than the actual ruby.  According to research by GIA labs, www.gia.edu/gia-news-research-nr41009 fusion by glass can be simply an adhesive method to closing major fissures.   The facts surrounding glass treatments may not be negative, as long as the price being paid is reflective of their value.

The more widely accepted treatment is infusing heat into the rubies which can enhance the colour and close existing fissures which provides for more of a “flawless” look to the gem.  http://www.professionaljeweler.com/archives/articles/1998/jul98/0798fys2.html.

So how does one decipher which type of treated stone holds more value?  Well, according to the Gemological Institute of America, “Rubies that have been diffused or that are glass filled are worth less than heated rubies”

The best practice for any jeweller is to educate their consumer so their customers understand the reason for the price and not make a purchase based under a false pretense of value.