One tool to make this measurement is the sclerometer.
From the en.wikipedia.org
The table below shows comparison with absolute hardness measured by a sclerometer, with pictorial examples.
From the en.wikipedia.org
More examples
A measuring instrument that measures the hardness of materials by penetrating them with a stylus that has a diamond point
The sclerometer, also known as the Turner-sclerometer (from Ancientu00A0Greek: u03C3u03BAu03BBu03B7u03C1u03CCu03C2 meaning "hard"), is an instrument used by metallurgists, material scientists and mineralogists to measure the scratch hardness of materials. It was invented in 1896 by Thomas Turner (1861u20131951), the first Professor of metallurgy in Britain, at the University of Birmingham.