From Wikipedia,
the free encyclopedia
Cleavage, in
mineralogy, is the tendency of
crystalline materials to split
along definite planes, creating
smooth surfaces, of which there
are several named types:
- Basal cleavage: cleavage
parallel to the base of a
crystal, or to the plane of the
lateral axes. This occurs quite
easily in
graphite, making the
material feel slippery.
- Cubic cleavage: cleavage
parallel to the faces of a
cube. This is the source of
the cubic shape seen in crystals
of ground
table salt (sodium
chloride).
- Diagonal cleavage: cleavage
parallel to a diagonal plane.
- Lateral cleavage: cleavage
parallel to the lateral planes.
This is of technical importance
in the
electronics industry and in
the cutting of
gemstones. While precious
stones are generally cleaved by
impact, man-made single crystals
of
semiconductor materials are
generally sold as thin
wafers which are much easier
to cleave. Simply pressing a
silicon wafer against a soft
surface and scratching its edge
with a
diamond scribe is usually
enough to cause cleavage; however,
when dicing a wafer to form chips,
a procedure of scoring and
breaking is often followed for
greater control. The vast majority
of commercial semiconductors (Si,
Ge,
GaAs,
InSb, etc.) are
diamond cubic, a
space group for which
octahedral cleavage is observed.
This means that some orientations
of wafer allow near-perfect
rectangles to be cleaved.
