Optical measurements indi- cate that the optical features of each organic material is similar to those of the monoaxial optical-negative-crystal usually,and approach to those of the materials with twin axes during the anthrazite period.

• 光性测定表明,一般情况下有机质各显微组分的光性特征与一轴负光性晶体相似,至无烟煤阶段与二轴光性物质的特征接近。