Mohs Scale of Hardness


Mohs Scale of Mineral Hardness
»  The Mohs scale of mineral hardness is a qualitative ordinal scale that characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material.
»  This scale was devised by the German mineralogist Frederich Mohs in 1812, who selected the ten minerals because they were common or readily available.
»  This scale is a chart of relative hardness of the various minerals (1 - softest to 10 - hardest).
»  The scale is not a linear scale, but somewhat arbitrary.
»  Despite its simplicity and lack of precision, the Mohs scale is highly relevant for field geologists, who use the scale to roughly identify minerals using scratch kits.
»  The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is four times as hard as corundum. The table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples.


List of Substances and Mohs Scale Hardness
Mohs hardness
Mineral
Chemical formula
1
Talc
Mg3Si4O10(OH)2
2
Gypsum
CaSO4·2H2O
3
Calcite
CaCO3
4
Fluorite
CaF2
5
Apatite
Ca5(PO4)3(OH−,Cl−,F−)
6
Orthoclase feldspar
KAlSi3O8
7
Quartz
SiO2
8
Topaz
Al2SiO4(OH−,F−)2
9
Corundum
Al2O3
10
Diamond
C

»  Mineral harness is also important in sedimentary rocks. Harder minerals tend to be able to travel longer distances down river systems. Quartz can often undergo several cycles of erosion, transportation and lithification ( change of sediments to rock). Zircons are persistent minerals in the environment and can often tell geologists the types of rock that were the original source rock for metamorphic or sedimentary rocks.
»  Mineral hardness can also be seen in the topography of many landscapes. Quartz bearing rocks are often more resistant to weathering and will produce the capstones that protect the tops of buttes and mesas from erosion.
»  Hardness of some other items:

2.5
Fingernail
2.5–3
Gold, Silver
3
Copper penny
4-4.5
Platinum
4-5
Iron
5.5
Knife blade
6-7
Glass
6.5
Iron pyrite
7+
Hardened steel file
>10
Wurtzite Boron Nitride
>10
Lonsdaleite (Hexagonal Diamond)


Most asked queries:
1.      How do you test the hardness of a mineral?
Answer: Mohs Hardness Test. As common sense dictates, Mohs Scale is based on the fact that a harder material will scratch a softer one. By using a simple scratch test, you can determine the relative hardness of an unknown mineral.

2.     How hard is glass?
Answer: Proceeding with the glass plate, the mineral is unable to scratch theglass (hardness = 5.5) at all. This mineral is about 4.0 on the Mohs scale. (If a mineral indeed scratches glass, you will be unable to wipe the scratch away.)

3.     How hard is a diamond?
Answers: Diamond is the hardest known natural material on the Mohs scale of mineral hardness, where hardness is defined as resistance to scratching and is graded between 1 (softest) and 10 (hardest). Diamond has a hardness of 10 (hardest) on this scale and is four times harder than corundum, 9 Mohs.

4.     How hard is gold?

Answer: In contrast, gold atoms slide past each other relatively easily, which makes the metal soft and malleable. Gold is so soft, in fact, that one gram of it can be beaten into a sheet covering nearly a square metre.
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