DIAMAGNETIC ORIENTATION OF CLAY MINERAL GRAINS

The orientations of diamagnetic mineral grains in magnetic fields are observed, for the first time, in suspensions of clay minerals such as talc, kaolinite and sericite. The minerals consist of two-dimensional crystal layers which produce intrinsic diamagnetic anisotropy, DELTA-chi, in the unit cell. In the case of talc suspension with the average diameter of phi 2.4-mu-m and the thickness of 0.2-mu-m, the grains show full orientation in a magnetic field of less than 0.5 T. As the size of the grains becomes smaller, full orientation is achieved with higher fields. This size dependence occurs because the field-induced anisotropic energy of a grain is proportional to N-DELTA-chi, where N is the number of unit cells in the grain.