Chrysocolla
Chrysocolla is found in the oxidised zone of copper deposits and is often mixed with other stones, such as turquoise, malachite or quartz. Pure chrysocolla is a striking navy blue colour and too soft for jewellery use; most cabochons comprise chrysocolla mixed with other minerals to give striking blue and green tones. Hardness: 2.5-7 Mohs (depending on the amount of silica present).