The exceptions to this kimberlite connection occur where deep crust tectonic motion causes the heat and pressure required to form carbon into crystals. Micro diamonds in the Japanese island arc and macro crystals in the Higher geologic region of Canada are connected with lamprophyre dikes. Lamproite, another intrusive igneous rock, holds the diamonds discovered in the Australian Argyle and Ellendale mines. Microcrystals have been found in high-pressure growing rocks in China, Europe, Russia, and Indonesia. Small diamonds have also been found in a few meteorites. However, in all of these rocks, high pressure, high temperatures, and a carbon source were necessary for crystals to form.
crystals belong to the isometric diamond system, most often forming octahedral crystals. “Iso” means identical, and “metric” represents measure, so diamond usually contains approximately the same in all directions around their center. Quartz, most likely to be confused with rough crystals, designs hexagonal crystals, generally terminating on one end. Herkimer diamonds terminate on both ends, but the hexagonal crystals classify them as quartz crystals.
Diamonds have a particular gravity of 3.1–3.5. Quartz has a specific gravity of 2.6–2.7. In placer deposits, tumbled quartz pebbles and diamonds can seem similar. The difference in particular gravity, however, allows panning or sluice schemes to separate the two minerals. Specific gravity, equal to density, gives the lighter quartz travel significantly down the sluice or, in smaller particles, wash out of a pan earlier than the denser crystals. Shaker tables can also be used. When a shaker table is set correctly, quartz settles across the center of the table, and the heavier crystals progress up the table.
crystals rank as the hardest naturally occurring mineral. The Mohs Hardness Scale ranks minerals from softest to hardest, with talc, the softest mineral, rated as 1, and diamond as the hardest ranked at 10. This scale ranks all minerals. Diamonds can damage every other mineral, but only crystals can damage diamonds. Quartz, the most likely mineral to be substituted for crystals in uncut rough form, rates seven on the Mohs Hardness Scale. Hardness test kits can be purchased, but they only test through Mohs Hardness 9, corundum. Since corundum damages itself and everything softer, any mineral that corundum won’t damage is diamond.
Conversely, any mineral that corundum scratches isn’t a diamond. Complications with the hardness test include damage to the specimen and the necessity of testing a new, unweathered surface. A lower hardness records if the tested surface is weathered, but diamonds are resistant to weathering.
Diamonds don’t like liquid, so miners sometimes use grease to depart diamonds from other rocks and crystals. They pour a slurry of material to be sorted across a greased table. The crystals stick in the oil while the rest of the material is carried across the table. Also, approximately 30 percent of crystals fluoresce under shortwave ultraviolet glow, regularly showing up as light blue and possibly shining white, yellow, orange, or red. After checking for cleavage, which is fracturing along planes parallel to the crystal faces, this test should be avoided by intentionally breaking the potential diamond.