1. Major element in a mineral, for which a trace amount of another element may substitute, e.g. Mg (the carrier element) replaced by Ni (the trace element) in olivine.

2. Inactive material, isotopic with a radioactive transmutation product, which is added to act as a carrier for active material in subsequent chemical reactions. Carrier elements are used in analyses of small samples, as the mass of radioactive material produced in a nuclear reaction is usually too small to be suitable for ordinary analytical procedures such as precipitation and filtration.