Although most elemental metals have higher densities than nonmetals, there is a wide variation in their densities, lithium being the least dense (0.534 g/cm) and osmium (22.59 g/cm) the most dense. Some of the 6d transition metals are expected to be denser than osmium, but their known isotopes are too unstable for bulk production to be possible Magnesium, aluminium and titanium are light metals of significant commercial importance. Their respective densities of 1.7, 2.7, and 4.5 g/cm can be compared to those of the older structural metals, like iron at 7.9 and copper at 8.9 g/cm. The most common lightweight metals are aluminium and magnesium alloys.