Diamonds mined today were actually formed millions of years ago.
A diamond is the hardest natural substance known to man. It's actually a crystal that forms in the earth's mantle, deep below the surface, when carbon atoms melt and re-harden. Deep-source volcanic eruptions eventually force diamonds toward the surface. The intense heat and pressure account for the diamond's hardness.
Moh Scale
The Moh scale ranks 10 minerals in ascending order of hardness. Talc, the softest mineral on the scale, is ranked number one. Diamond, the hardest, is ranked 10. Substances that don't appear on the scale can be rated according to their hardness compared to the hardness of minerals that do appear on the sale. Some common substances are assigned a fixed place on the scale. Fingernail, for example, is rated 2.5.
Testing Method
Kits are available that contain rods with fragments of the minerals listed on the Moh scale. The tester hits the mineral in question with a rod and makes note of which mineral the rod contains, and whether or not the rod scratched the mineral. Some kits have samples of the actual minerals. The tester swipes these against the mineral being tested. Only diamond can scratch a diamond, so a test kit with a diamond sample would definitively determine that the mineral being tested is also a diamond, if no sample besides the diamond could scratch it.
Significance
Knowing how hard a mineral is makes it much easier to identify. Using the Moh scale, for example, a mineral that scratches calcite, which is number three on the sale, but does not scratch fluorite, which is number four, obviously has to be a mineral known to be harder than calcite but softer than fluorite. The common non-mineral substances with fixed ratings help narrow the choices. As noted, a substance that no other substance scratches except a diamond is itself a diamond.
Knoop Test
An alternative method of testing the hardness of diamonds is the Knoop Test, developed in the 1930s by the National Bureau of Standards, which is now known as the National Institute of Standards and Technology. This test measures a substance's hardness according to how difficult it is to indent. The tester pushes the indent object into the surface of a smoothly polished diamond with a measured degree of force. It's held there for several seconds. The tester then removes the tool and measures the size of the indentation. The size of the indentation identities the substance as a diamond if, when measured, the indentation equals the anticipated size of a diamond's indentation.
Tags: being tested, diamond sample, Knoop Test, mineral being, mineral being tested, size indentation, that appear
