<P> On the Mohs scale, a streak plate (unglazed porcelain) has a hardness of approximately 7.0 . Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale . </P> <P> The table below incorporates additional substances that may fall between levels: </P> <Table> <Tr> <Th> Hardness </Th> <Th> Substance or mineral </Th> </Tr> <Tr> <Td> 0.2--0.3 </Td> <Td> caesium, rubidium </Td> </Tr> <Tr> <Td> 0.5--0.6 </Td> <Td> lithium, sodium, potassium </Td> </Tr> <Tr> <Td> </Td> <Td> talc </Td> </Tr> <Tr> <Td> 1.5 </Td> <Td> gallium, strontium, indium, tin, barium, thallium, lead, graphite, ice </Td> </Tr> <Tr> <Td> </Td> <Td> hexagonal boron nitride, calcium, selenium, cadmium, sulfur, tellurium, bismuth, gypsum </Td> </Tr> <Tr> <Td> 2--2.5 </Td> <Td> halite (rock salt) </Td> </Tr> <Tr> <Td> 2.5--3 </Td> <Td> gold, silver, aluminium, zinc, lanthanum, cerium, Jet (lignite) </Td> </Tr> <Tr> <Td> </Td> <Td> calcite, copper, arsenic, antimony, thorium, dentin </Td> </Tr> <Tr> <Td> 3.5 </Td> <Td> platinum </Td> </Tr> <Tr> <Td> </Td> <Td> fluorite, iron, nickel </Td> </Tr> <Tr> <Td> 4--4.5 </Td> <Td> steel </Td> </Tr> <Tr> <Td> 5 </Td> <Td> apatite (tooth enamel), zirconium, palladium, obsidian (volcanic glass) </Td> </Tr> <Tr> <Td> 5.5 </Td> <Td> beryllium, molybdenum, hafnium, glass, cobalt </Td> </Tr> <Tr> <Td> 6 </Td> <Td> orthoclase, titanium, manganese, germanium, niobium, rhodium, uranium </Td> </Tr> <Tr> <Td> 6--7 </Td> <Td> fused quartz, iron pyrite, silicon, ruthenium, iridium, tantalum, opal, peridot, tanzanite, jade </Td> </Tr> <Tr> <Td> 7 </Td> <Td> osmium, quartz, rhenium, vanadium </Td> </Tr> <Tr> <Td> 7.5--8 </Td> <Td> emerald, hardened steel, tungsten, spinel </Td> </Tr> <Tr> <Td> 8 </Td> <Td> topaz, cubic zirconia </Td> </Tr> <Tr> <Td> 8.5 </Td> <Td> chrysoberyl, chromium, silicon nitride, tantalum carbide </Td> </Tr> <Tr> <Td> 9 </Td> <Td> corundum, tungsten carbide, titanium nitride </Td> </Tr> <Tr> <Td> 9--9.5 </Td> <Td> silicon carbide (carborundum), titanium carbide </Td> </Tr> <Tr> <Td> 9.5--10 </Td> <Td> boron, boron nitride, rhenium diboride (a-axis), stishovite, titanium diboride </Td> </Tr> <Tr> <Td> 10 </Td> <Td> diamond, carbonado </Td> </Tr> <Tr> <Td>> 11 </Td> <Td> nanocrystalline diamond (hyperdiamond, ultrahard fullerite), rhenium diboride (c - axis) </Td> </Tr> </Table> <Tr> <Th> Hardness </Th> <Th> Substance or mineral </Th> </Tr>

How hard is graphite on the mohs scale