Columbia River Sand, US-Canada Boundary

Transmitted Circular Polarized Light and Reflected Darkfield Illumination

Definition/Function:

This deposit sample was part of a study for the distribution of slag particles introduce into the Columbia River from a smelter upstream.

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.

Characteristic Features:

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.

Associated Particles:

References: