The Mhos Scale ~ named after the German who first quantified it ~ is a range of numbers from 1 to 10 each describing the hardness of a specific mineral. 1 ~ talc ~ being the softest (powdered talc is ground down from the soft rock) and diamond ~ 10 ~ the hardest.
The idea is that the harder rocks ~ with the greater numbers on the scale ~ will scratch any of the minerals below them.
Although the standardized scale uses minerals, the range can be helpfully used to compare the hardness of many other materials for example ~
Some substances ~ wax for example ~ have a hardness of less than 1.
It is important to note that hardness does not equate to strength. It is fairly well known that glass can break if dropped or bent. Even diamond can shatter if maltreated.
There are many other specialist scales used to evaluate hardness and usefulness ~ expecially for metallurgists. Typically steels and other metals are often listed in the Rockwell Scale ~ which measures indentation rather than scratching. ISO ~ the International Standards Organization ~ has a fuller description of all this.
This note has exhausted my knowledge of this aspect of materials ~ readers will have to do their own further research.