CLEAVAGE STRESSES IN MINERAL CRYSTALS——WITH SPECIAL REFERENCE TO WOLFRAMITE AND MOLYBDENITE

Yu Xingzhen;Li Peilan Department of Geology, Central-South University of Technology  

The microstructural features of cleavage planes and cleavage fissures of molybd-enite and wolframite were studied usisg the scanning electron microscopy. Thesecondary electron images of the cleavage planes show that the planes are notsmooth ones but cleavage steps of varying patterns (river-like, linear and simple "λ"shapes). The secondary electron images of the cleavage fissures show that the endof the fissure is sharp and that the only difference of the fissures lies in whether they are closed or open. Whether cleavage steps are simple or complex and cleavagefissures are open or closed depends entirely on the development level of the cleav-ages of mineral crystals. According to Griffth's rift theory and dislocation theory, the above-mentionedmicrostructures of the cleavages show that: the cleavages of mineral crystals actuallybelong to brittle transcrystalline rifts. The process of rifting involves three develop-ment stages, i. e. nucleation, propagation, and transcrystallization and separation ofcleavage fissures. The mechanisms of the three stages are slide or climbing of dislo-cation. The process of clogging and destruction of cleavage dislocation in crystalsbrings about the formation of various cleavage stresses, such as nucleation, propaga-tion and transcrystallization of fissures. On the basis of thermodynamics, thesestresses are derived from internal thermal stresses of crystals and external stresses(including geological stresses and artificial stresses).

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