MICA SHAPE FACTOR AND ITS EQUIVALENT SEDIMENTATION IN THE SEDIMENTS OF THE YELLOW RIVER ESTUARY

Mica has a unique sheet-like structure and crystal form. In order to study the hydraulic difference between mica and other granular detrital minerals, light and heavy minerals were identified for the sediments of different size taken from the Yellow River Estuary. Muscovite and the biotite with different weathering degree were selected as research objects. The particle size and thickness of about 12 000 detrital mica from 5 samples were measured to study the equivalent size for sheet-like mica and granular feldspar and quartz in water. The results show that the content of mica in the Yellow River sediments is about 1.8%～9.7% in general, which vary greatly between different samples and different grain size grades and the content of mica decreases sharply from high to low around the grain size of 1.5Φ～5.5Φ. The thickness of mica is mostly less than 20 μm with an average of 8.93 μm. Muscovite is generally thinner than biotite. The volume of sheet shaped mica is approximately 16% to 55% of granular minerals, which is much smaller than those of feldspar and quartz. The volume change of mica can be described with shape factor and the diameter-thickness ratio, which varies between 5～60. According to the Corey and Stokes law, for mica and granular minerals such as feldspar and quartz, the sedimentation rate of mica is only 0.12%～0.33% of that for feldspar and quartz if they are the same in grain size. If the sedimentation rates are same for the two kinds of sediments, the grain size distribution of mica is wider than that of feldspar and quartz, with a difference of about 1.0Φ～1.5Φ. Therefore, the hydraulic behavior of sheet-like mica and granular feldspar and quartz are obviously different in the process of transportation and deposition. Equivalent deposition often makes large-particles of mica deposited together with fine-grained muddy deposits.