Calcite Mohs number

Hardness characteristics—especially in calcite crystals— may vary as a property dependent upon the direction of the scratch (i.e., able show evidence of a particular Mohs number if scratched along one face or direction as opposed to a different hardness number if scratched in a different direction. 

Calcium carbonate has a number of crystal modifications,but the calcite form is the one that is principally used for filler appHcations. Pure calcite is a relatively soft material (Moh hardness 3.0) with a specific gravity of 2.7. 

A mineral s hardness is defined as its ability to scratch another mineral. This is usually measured using a comparative scale devised about 200 years ago by Friedrich Mohs. The Mohs scale lists ten common minerals, assigning to each a hardness from 1 (talc) to 10 (diamond). A mineral can scratch all those minerals having a lower Mohs hardness number. For example, calcite (hardness three) can scratch gypsum (hardness two) and talc (hardness one), but it cannot scratch fluorite (hardness four). 

In 1812, German geologist Frierich Mohs (1773-1839) devised a scale with specimen minerals that offered comparison of hardness qualities that allows the assignment of a Mohs hardness number to a mineral. Mohs scale utilizes ten specific representative materials that are arranged numerically from the softest (1) to the hardest (10). The reference minerals are (1) talc, (2) gypsum, (3) calcite, (4) fluorite, (5) apatite, (6) orthoclase feldspar, (7) quartz, (8) topaz, (9) corundum, and (10) diamond. 

Mohs scale A scale that measures the hardness of minerals by their ability to scratch one another. A mineral is given a number on Mohs scale according to its ability to scratch one of the reference materials. In order of increasing hardness 1, talc 2, gypsum 3, calcite 4, fluorite 5, apatite 6, feldspar 7, quartz 8, topaz 9, corundum 10, diamond. 

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