a. light rare metals: including Li, Rb, Cs, Be, with little proportion and strong chemical activity

b. rare refractory metals: including Ti, Zr, Hf, V, Nb, Ta, Mo,W, with rather high melting points and their compounds with C, N, Si and B also have rather high melting points

c. rare dispersed metals (shortened as dispersed metals): including Ga, In, Tl, Ge, Re, Se and Te, most of which existed in minerals of other elements

d. rare earth metals: including Sc, Y and lanthanide, they have very similar property and co-existed in minerals.