The Journey of a Gem on Instagram: "October birthstones: Opal & Tourmaline. You don’t get one, but two birthstones and they couldn’t be more different!! Opal (hardness 5.5–6.5) - inky gemstone to display the phenomenon known as play of colour. BUT not all opals display this phenomenon, those that don’t are known as potch opals. Its play-of-colour comes from tiny silica spheres that bend light, and it actually contains water (most commonly 10%), which means if it dries out, it can crack! 🌈 Tourm