Lots of minerals are made of just 1 element: native copper for example, or native gold.
Native mercury, though, isn’t a solid at room temperatures and pressures — it’s a liquid. This native mercury probably formed as solid crystals under extreme pressure; however, now that they are at the surface of the Earth, they are reverting back to liquid and seeping out of the rock. Each shiny speck on this rock is a drop of liquid mercury sitting on the surface of the rock as high-surface-tension liquid drops!
Bryn Mawr Vaux Collection, Sample #559.