Puffed up and pulverized

Part of Hall of Meteorites.

D.3.2. Puffed up and pulverized.jpg

Both the pulverized rock, called rock flour, and the foamy-looking lechatelierite shown below are made of glass. They were originally part of the same layer of gray Coconino sandstone. Sandstone is made of quartz, a crystalline form of silicon dioxide. Under intense heat and pressure, quartz crystals turn into glass.

The presence of these two types of rock is clear evidence that a meteorite impact briefly compressed the sandstone. Only an impact can create such intense pressures on Earth's surface.

The porous lechatelierite was puffed to more than twice its original size by steam that was forced into the rock as the pressure released. The rock is now so light that it can float on water.

The rock flour contains grains of coesite, another type of quartz that forms under even higher pressure.