Aerogel

This is a rare sample of silica aerogel which is essentially a glass foam whose nano-structure contains up to 99.8% air, making it the world's lightest solid. It was made by Steve M. Jones, NASA Jet Propulsion Laboratory as part of the Stardust research project, which involved sending a spacecraft containing a large piece of aerogel on a close approach to the comet Wild 2 in order to collect space-dust. What made aerogel ideal for the mission was that, this ultra fine foam can gradually decelerate and capture dust particles in pristine condition. The process of then sifting through the aerogel, micron by micron, to identify and collect the space-dust was the world’s largest collaborative microscopy activity. The material appears to be much more invisible than glass despite being less transparent for there is no hint of reflection on its surfaces, giving it the appearance of not being fully solid. Its azure colour is not due to any pigmentation, but is caused by the same phenomenon that gives colour to our Earth's atmosphere, namely Raleigh scattering of light. In other words, it is blue for the same reasons that the sky is blue.