Diamond
                                        Although diamond is probably the most popular
                                        and discussed gemstone, it has probably been in
                                        use for a shorter time than any of the other gems
                                        that are commonly used in modern times. The
                                        reason for this is because lapidaries did not learn to
                                        fashion diamond until about the 15th Century when
                                        it was discovered that one diamond would abrade
                                        another.

                                        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.