Study On Characters Of Plastic Deformation In Brown Diamonds From Kimberlite Pipe Shengli No.1, Mengyin County, Shandong Province

This paper studies on the chosen polished slab brown diamonds which come fromkimberlite pipe Shengli No.1, Mengyin County, Shandong Province, for micro-characters by gem microscope and polarizering microscope, cathodoluminescence(CL), analysis by IR and Raman. There are four conclusions about internal charatersand causes of brown color in diamonds.(1) The diamonds were etched strongly. The etched lines can be seen on the surface ofdiamonds and they parallel each other in the same set, but across between two sets.(2) Most of these diamonds are abnormal birefringence. It shows that the parallelextinctions caused by the main plastic deformation planes are clear under crossedpolarizers, with two sets of parallel extinctions intersecting.(3) CL images show the internal characters and other growth information well. Thedifferent specimens show different information: regular zonal growth, complex zonalgrowth, agate-like growth and irregular growth.(4) The brown stripes through cross growth layers, and closely related to the parallelextinctions: the brown bands are surely accompanied by the parallel extinctions, butthe parallel extinctions do not guarantee to be accompanied by the brown bands.Raman shows the peak of diamonds change to lower wave-number direction and theaccompanying peaks appear meantime.The brown stripes caused by strong plastic defamation from above tests andanalysis.The plastic deformation occurred after the growth stage of diamond. Thisresult is important for gemology and mineralogy, and guide to enhance brown diamondtest later.