These are single diamond crystals from a diamond impregnated drill bit. The high
refractive index of diamond results in very high relief, the width of the black band at the edge of the particles.
Transmitted Off Crossed Polarized Light Illumination
Polycrystalline diamond abrasive has a conchordal fracture and is a prefered abrasive for use in abrasive impregnated
metal saw blades and drills. Its irregular shape provides more area mechanically locking the particle in the metal and
gives a sharper cutting surface. Single crystal diamond abrasive has a lower "cutting speed" and a shorter life on the
tool because its tetragonal shape results in a very low surface area to bond to the metal cutting tool and a rather dull
Significance in the Environment:
Diamond is isotropic, which distinguishes it from most other crystalline abrasives. Its very high refractive index, 2.42,
distinguishes it from other isotropic abrasives such as garnet, slag, and glass. This high refractive index results in
very strong relief at the edges of the particle.