Select a fresh, clean surface on the specimen to be tested.
Hold the specimen firmly and attempt to scratch it with the point of an object of known hardness. In this example, we use a sharp quartz (H=7) crystal .
Press the point of the crystal firmly against the surface of the unidentified specimen.
If the "tool" (in this case the quartz crystal) is harder, you should feel a definite "bite" into the surface of the specimen.
Look for an etched line. It is a good idea to rub the observed line with your finger to ensure that it is actually etched into the surface of the specimen. In this case, the crystal left a deep, definite scratch in the surface. Because the specimen was scratched by the quartz crystal, we know its hardness is less than that of the quartz - less than H=7.
If there is any question about the result of the test, repeat it being sure to use a sharp point and a fresh surface.