Hardness (H)
Web-Science.net
Mohs' Hardness Scale
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Credit: Klein, C. Manual of Mineral Science,
22nd edition.
22nd edition.
How to find the hardness of a mineral sample:
A test of hardness is really a comparison of one material against another material of known hardness.
Test kits usually have a quartz crystal. Quartz has a hardness of 7. If you scratch the pointed tip of the
crystal against a sample of window glass (H = 5.5), the quartz will scratch the window glass. Rub away
the fine powder and there will still be a scratch in the glass.
For example, if a pointed mineral is firmly rubbed against a softer mineral's fresh surface, then it will
scratch (or leave a groove in) the surface. Be careful, however, because if the mineral being scratched
is harder than the one used to do the scratching, then the softer mineral may leave a powder on the
surface that appears to be a scratch. Rub it off. If it is only on the surface and no scratch (groove) is
there, then the
A hardness test is a test of the ability of one thing to scratch another. For instance, a diamond would
scratch all the minerals on the scale. Talc would be scratched by all, but would scratch none.
To test the hardness of a mineral, rub a pointed part of it against minerals on the hardness scale. If it
scratches a mineral, it is harder than that mineral. Scratch it with minerals above the hardness of the
mineral it scratched. You have determined the hardness when you find the hardness range between
where the sample scratches and where it gets scratched.
Test kits usually have a quartz crystal. Quartz has a hardness of 7. If you scratch the pointed tip of the
crystal against a sample of window glass (H = 5.5), the quartz will scratch the window glass. Rub away
the fine powder and there will still be a scratch in the glass.
For example, if a pointed mineral is firmly rubbed against a softer mineral's fresh surface, then it will
scratch (or leave a groove in) the surface. Be careful, however, because if the mineral being scratched
is harder than the one used to do the scratching, then the softer mineral may leave a powder on the
surface that appears to be a scratch. Rub it off. If it is only on the surface and no scratch (groove) is
there, then the
A hardness test is a test of the ability of one thing to scratch another. For instance, a diamond would
scratch all the minerals on the scale. Talc would be scratched by all, but would scratch none.
To test the hardness of a mineral, rub a pointed part of it against minerals on the hardness scale. If it
scratches a mineral, it is harder than that mineral. Scratch it with minerals above the hardness of the
mineral it scratched. You have determined the hardness when you find the hardness range between
where the sample scratches and where it gets scratched.
A serious collector should also check this site to
understand variability in hardness in crystals relative
to crystallographic axis.
understand variability in hardness in crystals relative
to crystallographic axis.
Note: As with most things, there are exceptions. My intent is to keep this information as close to a middle school
level as possible and not delve into the exceptions and fine points. Refer to other literature for more information.
level as possible and not delve into the exceptions and fine points. Refer to other literature for more information.
| H |
| Mineral |
One rock characteristic you may use to help describe a mineral is hardness, represented
by the symbol H. A scale of hardness for different minerals is shown in Table 1. This
table, Moh's Scale of Hardness, shows ten minerals listed in order of decreasing hardness.
The hardest mineral, diamond, is located at the top (H = 10). The softest mineral, talc (H
= 1), is located at the bottom.
by the symbol H. A scale of hardness for different minerals is shown in Table 1. This
table, Moh's Scale of Hardness, shows ten minerals listed in order of decreasing hardness.
The hardest mineral, diamond, is located at the top (H = 10). The softest mineral, talc (H
= 1), is located at the bottom.
Table 1.
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| H |
| Object |
| Hardness of Common Objects |
Table 2.
What is Hardness (H) ?
offers to scratching. Another way to put it is to say that hardness = scratchability. The hardness of the
mineral to be tested is done by comparing it with other minerals and tools of known hardness. A scale of
hardness is used in making the comparison. This scale, called Mohs' Hardness Scale, is devised with the
softest known mineral at the bottom (H=1) and the hardest known mineral at the top (H=10).
mineral to be tested is done by comparing it with other minerals and tools of known hardness. A scale of
hardness is used in making the comparison. This scale, called Mohs' Hardness Scale, is devised with the
softest known mineral at the bottom (H=1) and the hardest known mineral at the top (H=10).