India is probably the oldest known source of
diamonds but South Africa became the major
supplier by the late 19th Century. Historic sources
of diamond have also been in Brazil. Review of
current literature such as Levinson (1998a, 1998b)
show that there have been important diamond finds
in California, Colorado, Russia, Australia and
Canada.
Diamond is composed of the element Carbon---it
crystallized in the isometric system; that is, there are
three crystallographic axes that are all of equal
length and are perpendicular to one another. In
addition to the axial relationships, the crystal can
have a center of symmetry, 3 axes of fourfold
symmetry, 4 axes of threefold symmetry, 6 axes of
twofold symmetry, and 9 planes of symmetry. In a
mineralogical text, these symmetry elements would
appear as: C, 3A4, 4A3, 6A2, 9P.
An isometric crystal can be defined by numerous
forms including a cube (6 faces), an octahedron (8
faces), a dodecahedron (12 faces), a pyritohedron
(12 faces), tetrahexahedron (24 faces), a
trapezohedron (24 faces) etc. To complicate issues,
one form may be superimposed over another such
as an octahedron modifying a cube such that the
cube appears to have its corners cut off. The
superimposition of faces can be quite extreme and
an isometric crystal can show several forms
superimposed over another. All of these different
modifications of the basic isometric crystal can exist
within a volume that fills a space occupying one
unit by one unit by one unit.
The hardness of diamond is 10 on the Mohs
Scale---there is nothing harder. The figure 10 could
be said represent the "average" hardness of a
diamond. Diamond is not equally hard on all of the
theoretical crystal faces that exist in the unit cube
above. The dodecahedral faces are just slightly
softer than the cube faces or the octahedral faces. If
the cube or octahedral faces are 10 hard, then we
may think of the dodecahedral faces as being
9.999… hard. It is this fact that makes it possible to
shape and polish diamonds. In this figure, the
crystal faces marked with d are just a bit softer than
the others; those softer faces make diamond
shaping and finishing possible.
Diamond crystals have 4 perfect cleavages that are
parallel to the octahedral crystal faces. These
cleavages are useful to the lapidary as they make it
possible to reduce a large, irregular shaped crystal
to smaller, more manageable pieces. Apparent
planes of cleavage where the stone might break
easily are usually selected as separation planes
when the crystal is cleaved. The cleavage operation
is carried out with a specially shaped chisel and
mallet. Many diamonds are now treated with a
diamond saw rather than cleaving but the skilled
diamond worker still must know the art of cleaving a
stone as this is the only some pieces can be
handled.
Diamond has a fairly high refractive index: 2.417.
That figure measures how much a beam of light is
bent and slowed down when it enters the diamond.
The high refractive index is what causes the
diamond to have its adamantine luster. Diamond has
a very high dispersion (0.044), the ability of a
substance to break white light down into its
component colors. The dispersion is what causes a
faceted diamond to show many colors when it is
moved about in the light.
Lapidary hobbyists have finished very few
diamonds. There are several reasons for this. First is
the availability of rough material. Most of the
world's diamonds are sold by a monopoly that
makes parcels of stones available to cutting houses
at sightings that are held only several times a year.
The parcels are priced at several millions of dollars
each and there is no high grading. The buyer must
buy either all or none. In many instances several
cutting houses must act together as one to
purchase a parcel of diamonds. This effectively
eliminates Corner Lapidary Shoppe from the list of
potential buyers.
On rare occasions, a piece of suitable rough
diamond might reach the hobbyist. The typical
faceting unit that is used by the hobbyist or even a
commercial colored stone lapidary won't begin to
handle a diamond. A small hobby unit will have a
1/30 horsepower to 1/15 Horse Power motor for
power. The units used for diamonds have at least a
one horsepower motor. The typical hobby unit will
have a 6 inch or 8 inch lap whereas the units for
diamond will have an 18 inch lap. The shaping and
polishing of a diamond generates enough friction
that a mechanical dop must be used as dop waxes
will melt when diamonds are being fashioned.
Neutral oil such as olive oil is usually used to
reduce friction in diamond finishing.
Proportions of the finished stone are important to
produce the best result. The diagram below shows
the ideal proportions for a diamond; these have
been determined both experimentally and in practice.
If the pavilion is too deep, the center of the stone
will appear dark and if is too shallow, the stone will
appear washed out.
A diamond appraiser will determine the weight of
the properly proportioned stone that can be derived
from a finished stone and use that as the weight of
appraisal. The cost of refashioning the diamond to a
properly proportioned stone is then deducted from
the evaluation. This prevents the lapidary from
inflating the price of the stone by inflating the
weight.
Diamonds are useful for several geological
purposes. Petrologists have thought that the tiny
inclusions in diamonds that are commonly called
"carbon spots" (but rarely are) and include such
minerals as pyrope garnet, olivene, and pyrrhotite
are tiny samples of the earth's mantle, that zone that
is about 30 miles beneath the earth's crust. Thus,
inclusions in diamonds may provide some examples
of the mantles makeup. Some geologists have
suggested that the distribution of diamonds
between continents shows examples of spreading
ocean basins and provides strong evidence for plate
tectonics.