Thread: Using Marble as a finishing stone

Marble is primarily a compacted form of calcite the mineral formed by the sedimentation of calcium carbonate. On the Mohs scale, which classified minerals by hardness (the ability to scratch minerals lower on the scale), calcite is rates as a level 3. That is pretty soft.

A knife blade or razor would rank somewhere around 5-6 on that scale depending on the degree of hardening. For comparison, your teeth are composed of a mineral called apatite (primarily Calcium phosphate with some trace elements) are around 5 on the scale. That is why your dentist can use a stainless steel dental pick to scale your teeth without scratching the enamel.

Most of hones are comprised of harder minerals such as Orthoclasse Feldspar (Potassium Aluminum silicate- 6 on the scale), Garnet and quartz/silica are about 7 on the scale, Beryl/Emerald (about 7.5 on the scale, Topaz/Aluminum silicate (8 on the scale), Corundum/Ruby/Sapphire/Aluminum oxide (9 on the scale). Even harder minerals are silicon carbide and cubic boron nitride which fall between 9 and 10 on the scale. Diamond, which is the hardest mineral known to man is ranked 10.

Thus, stropping on marble might help straighten the edge of a razor, just as linen and leather can do, but it it is not hard enough to hone the edge of the razor.