The Corundum Family- Think Sapphire and Ruby!

Corundum is sometimes the term for to the low grade rock like opaque sapphire and ruby. Often you can still see the crystal growth, in a hexagon shape like the rings of a tree’s growth. The ugliest of all corundum is used commercially, where it is ground down and used as an abrasive. But don’t forget even good grade ruby and sapphire is called corundum as it is from this family.


Everyone knows of the blue sapphire, it is a strong, hard gemstone. The closest to diamond for it’s toughness. This means you can wear sapphire everyday for generations and the facets and overall appearance will look as crisp and clean as when you first bought it. That’s why it is perfect for engagement rings.

Sapphires don’t just come in blue! Sapphire comes in many colours, in many shades of blue, green, pink ,purple, red or yellow, and you get colourless sapphire as it has had no minerals or trace elements to colour it as it was being formed in the earth.

The single sapphire is usually formed with two colours, it could be blue vertically and green or yellow along the horizontal axis or a dark blue one way and a light blue the other way. Only when two shades of the same colour can be seen then you can call it a pure blue or pure green sapphire.

stunning australian parti sapphire

A stunning example of an Australian parti sapphire

Parti Sapphires

In some sapphire, you will see two or three colours at once down one angle like blue, yellows and green. In Australia we call these parti sapphire and the United States of America calls them bi-color sapphires.

Sapphire are extremely bright. Sapphire can be colour banded or clean with no marks or it can have silk like appearance and it can be opaque and comes in all grades and quality, if you can see through it with no marks, then it is a very good grade sapphire.

Pure blue sapphire demands the highest price and always has.

When the sapphire is opaque they tends to be cut into cabochons (domes) , carved or  heavily treated to pretend it is a good one. Only about 95% of sapphire you see for sale is natural and untreated.

Here at Gemhunters we only trade in natural and untreated Gemstones!

When buying sapphires, you must always ask what has been done to your sapphire in the way of treatments as they are often is heated to remove the silk to make it look clearer forcing the price up.


Sometimes when opaque sapphire is cut into cabochons, a bright white 6 ray star is visible when near a light source, the star travels across the top of the dome. This effect is called a star sapphire. The silk like fibres also called rutile needles in the sapphire that makes this unique phenomenon that moved with the light. The effect is very appealing.




The Red Ruby is also corundum but it has the mineral chromium present. The chromium will distinguish red sapphire from a ruby. Burmese ruby is famous for being the best on the market.

Ruby comes in many shades of red. The more transparent or richer red or the bigger the ruby, the more valuable it is.

Some rubies have been heated at high temperatures, pumped with liquid glass into the cracks to make them look invisible. You could easily think it was a natural high quality ruby, but in fact it is not. Sadly these days unheated ruby is rare and extremely high value.

Ruby also can have a star like the sapphire when cut into a dome cabochon, usually the more opaque rubies with silk and rutile and chatoyancy are cut as cabochons, or else they are sent to be treated in all sorts of way to make them look more valuable.