Bismuth sulfide, , occurs naturally in bismuth ores. Bismuth compounds account for about half the production of bismuth. Such metals include lithium, niobium-tantalum, bismuth, antimony and rare earths. These metals were typically lead, antimony, bismuth or copper. Arsenic, tin, antimony, silver, gold, copper, and bismuth are common impurities in lead minerals. Alloying elements such as copper, antimony, bismuth, cadmium, and silver increase its hardness. Other exceptions include antimony and bismuth. This liquid bears important substances such as lead, silver, tin, bismuth, and antimony. Chalcogens also bond with other pnictogens, such as arsenic, antimony, and bismuth. Examples include gallium, ytterbium, bismuth and neptunium. Examples include gallium, ytterbium, bismuth, mercury and neptunium. Sulfur, gallium, selenium, iodine, and bismuth have medicinal applications. The content of bismuth and strontium creates some chemical issues. A combination of bismuth and tellurium is most commonly used for the thermocouples.