Columbia River Sand, US-Canada Boundary
This field of view contains three blast furnace slag grains.
Transmitted Circular Polarized Light and Reflected Darkfield Illumination
This deposit sample was part of a study for the distribution of slag particles introduce into the Columbia River from a
Significance in the Environment:
This field of view contains three blast furnace slag grains. This documents the fact that slag grains are entering the
river and are transported to the river edge by currents and tubulence in the river. The dense slag grains do not settle
out into the deeper channel and remain there. They are transported through the environment at least from river edge to
river edge, along with the heavy metals they contain.
Reflected darkfield illumination highlights reflective surfaces or optically heterogeneous materials or surfaces.
Particles that scatter light because of their heterogeneity tend to take on an orange cast. Particles that specularly
reflect light tend to be bright if the angle is correct. The three blast furnace slag particles are evident by their
opacity and their lack of reflection. The black blast furnace slag particles consist of a glass matrix with very small opaque,
metal oxide inclusions. They are not conductive and have low refractive indices relative to the black inclusions they
contain. The natural mineral black metal oxide grains in this sample are semi-conductors and have real refractive
indices far from 1.680, the mounting medium used in this case. The difference in refractive index and the fact that
they are semi-conductors results in easily detectable reflected light.