July birthday's birthstone - The Ruby

Birthstones are gems traditionally associated either with calendar months or zodiac signs, and they vary across the world.  The custom of wearing birthstone jewellery originated in 18^th- century Poland.

And so here we are in July: the month for rubies, those beautiful stones with their range of red hues.

Rubies are a variety of the mineral corundum (aluminium oxide).  Interestingly, sapphires are exactly the same mineral, just with a very different colour.  The reddish colour of a ruby comes from the presence of chromium.  So any form of corundum that is not red is classified as a sapphire.

True to its reputation for class, the ruby is one of the five cardinal gems, those traditionally regarded as the most valuable.  The others are diamond, emerald, sapphire, and amethyst.

Like other gemstones, the quality of a ruby is determined by the four Cs: colour, cut, clarity, and carat (weight).  Rubies are also evaluated by their geographic origin.

The finest rubies have always come from Burma (Myanmar).  Nearby, Thailand is the main source, with brownish red stones. Afghanistan, Pakistan, and Vietnam produce bright red stones, whilst those from India, Australia, the USA, Russia, and Norway are dark red, sometimes even opaque.

Here are a couple of rubies to get you excited:

The largest mined ruby in the world is the Liberty Bell Ruby, an 8,500 carat stone sculpted into the shape of a miniature Liberty Bell.  It was stolen in a robbery in 2011.  Despite the suspects being arrested, the stone has never been found. It’s worth a cool US$2 million.

But if you want truly eye-watering, then the most expensive ruby in the world is the Sunrise Ruby, selling at a 2015 auction for US$30 million!  I’ll take two, thanks!