Heavy metals is improved with the addition of thorium. Tellurium is added to copper and steel alloys to improve their machinability; and to lead to make it harder and more acid-resistant. The biocidal effects of some heavy metals have been known since antiquity. Platinum, osmium, copper, ruthenium, and other heavy metals, including arsenic, are used in anti-cancer treatments, or have shown potential. Antimony (anti-protozoal), bismuth (anti-ulcer), gold (anti-arthritic), and iron (anti-malarial) are also important in medicine. Copper, zinc, silver, gold, or mercury are used in antiseptic formulations; small amounts of some heavy metals are used to control algal growth in, for example,
Period 6 element a massive extraterrestrial object caused the extinction of dinosaurs and many other species 66 million years ago. It is thought that the total amount of iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum group metals, the high density and tendency of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten. Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term "platina", which is