Most researchers consider that Chijiadian garnet lherzolite in Datan of Shandong Provinceincludes mainly eclogite composed chiefly of omphacite garnet, with small amounts of intercalated garnet diopsidite. There exists controversy on relationship and material sources of eclogite and garnet diopsidite. Some geologists hold that the two sorts of rocks were derived fromdifferent sources, and some believe that garnet diopsidite was formed through alteration of eclogite. The author observed the existence of transitional relationship between eclogite and garnet diopsidite in garnet lherxolite of this area, with the former at the center, and the lattermaking up the fringe; in diopside of the fringe there appears irregular and lamellar omphacite.Based on investigations into petrological and mineralogical features as well as equilibrium T-Pconditions of rocks together with a comparison with the same sorts of rocks in different areas,the author holds that the two sorts of rocks are both basaltic rocks (e. g. gabbro) derived fromthe upper mantle. The elevation of pressure led to the appearance of garnet and the reduction ofplagioclase, forming the garnet, pyroxene and plagioclase assemblage. At that time, pyroxenewas dominated by Di, and at high temperature, Jd and Di made up a mixed binary system.Further elevation of pressure resulted in urmixing of solid solution, forming omphacite in diopside. At the same time, the ratio of garnet to pyroxene increased, and plagioclase became moreenriched in sodic materials, leading to the formation of garnet diopsidite assemblage. Under thehighest pressure, sodic plagioclase was decomPOsed into jadeite and entered solid solution toform omphacite. Moreover, Jd in diopside also increased and was gradually converted into omphacite, thus forming the mineral assemblage of eclogite.