If your birthday is in September then your birthstone is ✨ Sapphire ✨ Sapphire is a well known variety of the mineral corundum. And they can be a whole rainbow of colours. Except red. Because when corundum is red then that’s when it becomes a ruby. Any corundum that is not red is a sapphire. Easy peasy, right? Corundum in its purest state is colourless, but if you add ions of transition metals into the mix then you get a lovely rainbow of ‘fancy’ coloured stones. Sapphires are valuable gemstones