Tourmalines are an interesting addition to the gemstone family, as they are also found in multi-coloured types, whose origins go back hundreds of millions of years. Made of a type of boron silicate mineral, tourmalines are found predominantly in green to reddish hues, however, the range of hues in which the stones are numerous, from yellow to various shades of orange, and come in a relatively high level of durability, around 7- 7.5 level of Mohs scale of hardness. Tourmalines are not the most popular choice when it comes to engagement rings, however, they are gaining in recognition and depending on the colour, the gemstone can be considered to be of high value, with blue being the most valued. Tourmalines are sourced from a number of countries across the world, with Brazil being the most popular. As the birthstone for the month of October, Tourmalines can also be found in mixed coloured varieties, where a single gemstone carries two or more hues.