Sapphire is the gem variety of the mineral corundum. Although almost all people associate the term “sapphire” with the colour blue, sapphire gems occur naturally in colours as diverse as pink, orange, yellow and green. These are referred to as pink sapphires, orange sapphires and so forth. The only exception is red corundum, which is of course ruby and is consequently discussed further in the ruby guide.
Rubies are the gem variety of red corundum, the same mineral that is sapphire in any other colour. As such, they have a hardness equal to that of sapphires (9) and their resistance to chipping and scratching makes rubies the ideal gem for use in jewellery. Rubies are one of the most expensive gems available today and are mined in Mozambique, Sri Lanka, Myanmar (Burma), Thailand, Vietnam, China, Afghanistan, Kenya and Tanzania.
Emeralds, the gemstone variety of green beryl, are well-loved for their unique green colour and are one of the most popular gems available today. The vivid green exhibited by emeralds is a result of the presence of chrome and, sometimes, vanadium, in the crystal structure. Colombia, Brazil and Zambia are today the top producers of quality emeralds, but Russia, India, Austria are also significant producers.
Tanzanite is one of the world’s most unique and precious gems, considered to be 1000 times rarer than diamond. It is a variety of the mineral zoisite and is found in only one locality world-wide – at the foothills of Mount Kilimanjaro in northern Tanzania, East Africa. Although tanzanite’s unique colour, poised intriguingly between blue and violet, makes it highly desirable, it is a relatively soft and fragile gemstone.