A mineral is a naturally occurring , solid, crystalline substance with a specific chemical composition. Minerals are usually inorganic and are formed by ionic, covalent or metallic bonding. Ionic bonds are the dominant type of bonds in mineral strictures. 90% of all minerals are ionic compounds. Minerals bonded by covalent bonds are strong, for example carbon bonded together to form diamond. Metallic bonds are a type of covalent bonds where the atoms have a strong tendency to lose electrons and pack together as cations.
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There are several things that can help scientists evaluate which category something belongs to. The similarity in features is one of them. If two skulls looked alike, they were probably species of the same evolutionary category. For example say humans and monkeys rather than humans and dogs.
Similarly fossils have helped scientists categorise species. Study of the chromosomes (in cases with available chromosomes) can help scientists figure out a lot about the subjects and categorise them.
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