Fracturing as a sample preparation method of basalt for SEM analysis

Abstract

The article discusses a method for preparing basalts for HR-SEM analysis. This method involves fracturing samples under identical conditions using an Izod pendulum. Fractures propagate in a sample mainly along the grain boundaries; its cross pores and mineral inclusions, which are stress concentrators. That is why submicron mineral gains are revealed on fracture surfaces rather than on polished surfaces. Surfaces of fresh fracture were studied in basalt samples from the Etna vents and Tolbachik fissure zone. Crystals with zinc, copper, nickel, sulfur, and iron were found on surfaces of fresh fracture. The morphology was revealed of submicron crystals of apatite, orthopyroxene, spinel, and copper sulfide. These crystals have not been found on polished thin sections of the specimens, since they were not brought to the surface or were chipped out. The morphology of submicron inclusions in orthopyroxene and olivine were shown. The fracture surface, in contrast to the thin section surface, retains more information on zoning in rock-forming minerals. Features of the accessory minerals distribution, the morphology of crystals in pores, and the compound of minerals inside inclusions are presented more reliably on the fracture surface. The authors propose to introduce the fracture surface study into petrogenetic research.