Harder than a diamond?
New testing has shown that osmium (a metallic element) is less compressible that diamond. This means that under extremely high pressures it shrinks less than diamond. This opens a great potential for new "superhard" materials. What is unusual about this discovery is that normally materials of such stiffness come about through exposure to high temperatures and pressures, so it should generate a lot of questions to be answered about the nature of stiffness in materials.