"Scandium" is one of the 35 key minerals. Scandium-modified aluminum alloys, which are mostly used for lightweighting, have equal yield and tensile strength to steel and titanium alloys but are 1/3 the weight of steel and 40% lighter than titanium. They also have better corrosion resistance. Scandium has many applications in technology and science. It is used in special alloys that are resistant to heat and corrosion because they transform from one solid phase to another when scandium changes between two states: monoclinic and tetragonal. These alloys are important in technologies such as laser cutting tools, gas turbines, and nuclear reactors. It also forms a stable oxide that is less reactive with water and oxygen than other metals. This property makes scandium useful in medical devices that come in contact with blood or other fluids (such as heart valves and joint replacements). Finally, scandium compounds are active ingredients in some drugs. They are used to treat certain types of cancer and bone diseases because they inhibit enzymes that cause tumor growth and bone loss. Scandium is found in small amounts in most rocks, but it can be extracted from some elements including zinc, copper, silver, gold, lead, and lime. The main source is sea shells.