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Mohs
scale of mineral hardness
Mohs'
scale of mineral hardness characterizes the scratch resistance of various
minerals through the ability of a harder material to scratch a softer. It
was created, in 1812, by the German mineralogist Friedrich Mohs and is one
of several definitions of hardness in materials science.
A
good property in mineral identification is one that does not vary from
specimen to specimen. In terms of reliability, hardness is one of the
better physical properties for minerals. Specimens of the same mineral may
vary slightly from one to another, but generally they are quite
consistent. Inconsistencies occur when the specimen is impure, poorly
crystallized, or actually an aggregate and not an individual crystal.
| Hardness |
Mineral |
Absolute Hardness |
| 1 |
Talc |
1 |
| 2 |
Gypsum |
3 |
| 3 |
Calcite |
9 |
| 4 |
Fluorite |
21 |
| 5 |
Apatite |
48 |
| 6 |
Feldspar |
72 |
| 7 |
Quartz |
100 |
| 8 |
Topaz |
200 |
| 9 |
Corundum |
400 |
| 10 |
Diamond |
1500 |
You
use the Mohs scale by testing your unknown mineral against one of these
standard minerals. Whichever one scratches the other is harder, and if
both scratch each other they are both the same hardness.
The
Mohs Hardness Scale starting with talc at 1 and ending with diamond at 10,
is universally used around the world as a way of distinguishing minerals.
Simply put; the higher the number, the harder the mineral.
The
Mohs scale is strictly a relative scale, but that's all that anyone needs.
In terms of absolute hardness, diamond (hardness 10) actually is 4 times
harder than corundum (hardness 9) and 6 times harder than topaz (hardness
8). Because it isn't made for that kind of precision, the Mohs scale uses
half-numbers for in-between hardnesses.
There
are a few handy objects that also fit in the Mohs scale. A fingernail is 2½,
a penny is just under 3, a knife blade is 5½, glass is 5½, and a good
steel file is 6½. |
