A variety of chalcedony is carnelian, which is used exclusively for the production of gemstones and is characterised by an opaque or only slightly translucent appearance. Carnelian occurs in almost every conceivable shade of brown as well as in bright red and can appear in a single colour as well as striped or spotted. The colour changes depending on the quantity of iron oxide and iron hydroxide present. The oxide colours the stone red, while the hydroxide content is responsible for the brown colour. Carnelian is mainly mined in Brazil, India, Madagascar and Uruguay and is ideally suited for jewellery processing due to its hardness grade 7 on the Mohs scale.