How do I test the hardness of a rock?

Question

I need to find the PSI/Hardness of a rock. Where would I send it to or how can I figure this out on my own? Its limestone if that helps.

Answer 1

Although there is a lot a variability in limestone, it is typically listed with a hardness of 3 on the Mohs scale.

Answer 2

Well to test the hardness of limestone on the Moh scale you can try and stretch it with other rocks. Mohs scale goes from one to ten and it is meant to show how well rocks can hold up to abrasions. Just to let ya know limestone is a 3-4 on the scale. But to test that you can do several things. You could try and scratch it with known rocks on the scale. for example if you rubbed quartz on it the limestone would scratch so you know it is softer then quartz then you could rub talc or gypsum and the limestone wouldn't scratch so you know it is harder then those. and you can narrow down like that. Or use junk to test it for example your fingernail is 2.5 a penny is 3.5 a steel nail is 5.5. stuff like that. hoped that helped oh and here is moh's scale.

1 = Talc

2 = Gypsum

3 = Calcite

4 = Fluorite

5 = Apatite (fluorapatite)

6 = Orthoclase

7 = Quartz

8 = Topaz

9 = Corundum

10 = Diamond

Answer 3

If it is for commercial purposes you would need to use an accredited lab to to the strength testing. Rock mechanics labs are not exactly in every town but your nearest civil engineering firm would know of one. Universities with a geology school have the equipment but probably not the certification requirements.

Even rocks of the same composition vary greatly in hardness and strength.

Answer 4

The type of "hardness" you are talking about has nothing whatsoever to do with Moe's hardness which is a scratch test used to test minerals. The numbers it uses are not equally spaced but are based on which mineral will scratch the one below it for example corundum is 9 and diamond 10 on Moe's scale but in absolute terms if corundum is 9 diamond should be over 1000.

The type of test you require is, I am sorry to say, not possible to do at home. Cylindrical cores of rock are cut from various places in your deposit, trimmed and then placed in between the jaws of a hydraulic press and it is pressurized to the point where the sample crushes. The force at this point is recorded and from the size of the core used the strength of the sample is calculated. A more advanced form of this test is known as a triaxial test where the sample is contained within a testing cell and it is pressurized all round to simulate the rock's strength when in situ. The machines to perform these tests are large, heavy (several tons) and expensive. There are however many companies that perform this type of testing on a contract basis at a very reasonable cost.

Hope that helps a little.

Answer 5

Scratch it with another rock with a known hardness

There is a scale of hardness known as Moh's scale in which 10 minerals are used as standrds for hardess with 1 being the softest and 10 being the hardest

the scale

1. talc

2.gypsum

3.calcite

4.flourite

5 apatite

6. orthlocase

7. quartz

8. topaz

9. corundum

10. diamond

also some common items are also used

Fingernail 2.5

penny 3

glass 5.5