Chalcedony
According to Rock & Gem, 'chalcedony is one of the most ancient gemstones' (Blue Chalcedony: A lapidary Superstar). It has the same chemical makeup as quartz, but chalcedony is a microcrystalline which means its crystals cannot be seen with the naked eye. It is softer than quartz, but the dense crystal structure gives it more strength. Blue chalcedony is a sought-after mineral by gem cutters and collectors around the world due to its limited availability in the market.