| hardness | <chemistry> Total concentration of calcium and magnesium ions, expressed as the equivalent concentration (mg/L) of calcium carbonate. Hard water is water that contains lots of calcium carbonate and other minerals. (09 Oct 1997) |
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| hardness scale | A qualitative scale in which minerals are classified in order of their increasing hardness, based on the fact that the harder of two materials will scratch the softer and will not be scratched by it. The scale lists 15 substances: 1, talc; 2, gypsum; 3, calcite; 4, fluorite; 5, apatite; 6, orthoclase, periclase; 7, vitreous pure silica; 8, quartz, stellite; 9, topaz; 10, garnet; 11, tantalum carbide, fused zirconia; 12, fused alumina; 13, silicon carbide; 14, boron carbide; 15, diamond. Synonym: Mohs scale. (05 Mar 2000) |
| Brinell hardness number | A number related to the size of the permanent impression made by a ball indenter of specified size (usually 10 mm in diameter) pressed into the surface of the material under a specified load: where P = applied load in kg, D = diameter of the ball in mm, and d = diameter of the impression in mm. (05 Mar 2000) |
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| Knoop hardness number | A number obtained by dividing the load in kg applied to a pyramid-shaped diamond of specific size divided by the projected area of the impression: KHN = L/A, where A= the projected area of the impression in mm2 and L= the load in kg; used for measurements of hardness of any materials, especially very hard and brittle substances such as tooth dentin and enamel. (05 Mar 2000) |