The element neon has no hardness on either moh's hardness scale or rockwell scale unless it is frozen. These scales measure only solids.

One of the scales is a durometer. The appropriate scale depends on the industry the hardness is being tested for.

Aluminium has a Mohs hardness of 2.75.

There are other hardness scales, such as Vickers and Brinell, and these numbers will differ. Each of these scales has a particular field of application.

The big two are the Rockwell and Mohs Scales.

Converting between different hardness scales is not an exact science, but there are many charts available that will show the approximate relationship between different scales.

One chart is available at http://www.carbidedepot.com/formulas-hardness.htm

Another useful website for converting between different hardness scales is http://www.efunda.com/units/hardness/convert_hardness.cfm Tianxing Testing Instruments Co. Ltd. is a professional manufacturer of portable hardness testers http://www.hardnesstesters.biz/