# Why is diamond not the most dense substance?

Diamond is the hardest substance on earth which can be attributed to its tightly-bonded crystal lattice. Hence, assuming there were a substance more dense than diamond (which there are), mustn't it be harder than Diamond?

• The tightly-packed crystal structure of diamond is only one of the factors involved in determining its hardness, but I do recall reading that diamond is the material with the highest atomic density (atoms per cubic centimeter) in ambient conditions, though graphene probably beats it when it comes to area density (atoms per square centimeter). Aug 16, 2022 at 14:22
• Mercury is about 4 times denser than diamond and it it a liquid. Graphite is also made of carbon, but is relatively soft. Gold is nearly six times denser but is also so soft when pure you can mark it with your fingernail. Perhaps hardness is more complex than you think. Aug 16, 2022 at 15:18

Osmium has the highest density among chemical elements, being more than 6 times denser than diamonds with $$\pu{22.6 g cm-3}$$ versus $$\pu{3.52 g cm-3}$$. Gold with $$\pu{19.5 g cm-3}$$ should be one of hardest materials, what is obviously not true as it is very soft.