Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones. Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. Quartz is rated at a 7 on the Mohs hardness scale. Quartz is thought to balance the aura and electromagnetic energy and is associated with all chakras as a cleansing stone. Quartz is also thought to amplify the thought and meditative process.