The ruby is one of the most famous gemstones in the world due to its characteristic red colour. This colour is also what makes the mineral a popular gemstone. But not only the colour of the ruby, also other characteristics make it a frequently used element in the most different jewellery creations. Ruby belongs to the mineral class of oxides and hydroxides and is a variety of corundum. The chemical formula for rubies is Al2O3 and they have a glass to diamond luster. Their transparency is transparent, but can also be opaque. The typical red colour of rubies can be traced back to small amounts of chromium contained in them. If a corundum is not red, but pink, blue or other colored, they are not called rubies, but sapphires. The name ruby comes from the Latin word rubens, which means red. As a component of jewellery, rubies are often provided with a special facet cut, which ensures an individual and sparkling refraction of light. The stronger the red colour, the more sought-after rubies are. They are even more valuable if they also have a slight blue cast, whereby the ruby colour is reminiscent of pigeon blood, which is used as a quality describing characteristic.