Pencil debris includes the graphite, paint flakes, sawdust, and erasure debris.
The "lead" in a pencil is actually graphite with a clay binder. The clay binder helps prevent the rapid loss of graphite and
makes the lead hard, a desirable quality if a fine line is to be drawn. The pencil hardness increases with more clay binder.
Graphite has an hexagonal crystal structure and cleaves easily normal to the "c" axis. Graphite has a reflectivity of around 24% on
the cleavage plane and about 4% or less away from that plane. The high reflectivity of the cleavage plane helps identify these
particles. Another characteristic is the change in polarization direction at the edge of the particles when view with crossed
polarized light due to the electrical conductivity of graphite.
The most common type of erasure on school pencils is "pink pearl". Other erasure materials are common in office buildings.
The most common paint color on pencils used in schools is yellow.