Mirka Trajanova

Structural and textural characteristics of slate and its response to the point load test

From the geomechanical point of view slate is considered to be one of more trying rock varieties. The results of research have shown close relationship between structural, textural and mineralogical characteristics on the one hand, and its strength and resistance to point loads on the other hand. Its weakened zones are the result of anisotropy. They develop mainly due to dynamo-metamorphosis of the primary mudstone, resulting in the formation of the secondary slaty cleavage, with a pronounced preferred orientation of the phyllosilicates. Low strength is the consequence of the weak Van der Waals chemical bond between individual packets of the internal crystal structure of the sheet minerals, particularly sericite. Bedding and microfolds with a crenulated structure and partial preferred orientation of sheet minerals, as well as directions that are weakened with sigmoidal shear deformations as the predecessors of microfaults, also result in significant but less problematic anisotropy. Thin lepidoblastic lamina, in apparently massive sandy metasiltstone beds in the slate represent discontinuities, which have a decisive influence on the reduction of their strength. doi:10.5474/geologija.2006.019 254 Mirka Trajanova & Ana Mladenovi~