The Mohs Scale of Hardness was created in 1812 by German geologist/mineralogist Friedrich Mohs. This method of hardness judgement is based on the ability of one sample of matter to scratch another. So a mineral ranked 8 out of 10 is harder and will scratch a mineral ranked 3. When the scale was designed, the hardest known substance is diamonds, so naturally diamonds are rated a 10 out of 10. This scale is a ordinal scale as it doesn’t show the rating for absolute hardness, it is to show which minerals are harder as compared to each other. It was created using 10 commonly found minerals and rated based on observations made.
To give you a sense of where other common items rate; your fingernail is about a 2.5. A copper penny is roughly 3.2, pocketknife is 5.1, glass rates about 5.5, and a steel needle is a 6.5. Most Granites rate about a 7 in the scale while most marbles, limestones, travertines rate in the 3 area.
Observations of mineral
|1||Talc||Very easily scratched by the fingernail.|
|2||Gypsum||Can be scratched by fingernail|
|3||Calcite||Very easily scratched with a knife and/or a copper coin. This is where most Marbles, limestones, travertines, rate.|
|4||Fluorite||Can be scratched by a knife.|
|5||Apatile||A knife has difficulty scratching this mineral; glass is rated in this hardness.|
|6||Orthoclase||Cannot be scratched with a knife. This mineral can scratch glass with some difficulty.|
|7||Quartz||Can scratch glass easily. This is where most granites are rated in terms of hardness.|
|8||Topaz||Can scratch glass very easily.|
|9||Corundum||Can cut glass.|
|10||Diamond||Can scratch virtually anything, is commonly used to cut glass and stone.|