Sedimentary Mars

While there seem to be an infinite number of rocks based on slight differences in minerals, they can be grouped into only a few very basic types.

NASA dollars at work, learning about how awesome the
universe is!

Sedimentary rocks form from bits of rock and mud eroded from older rock.  They are classified by the size of the particles they are made of.  Shales, for instance, are made of mud and clay that settle to the bottom of calm waters.

They look like this photo.  This particular type of rock is technically mudstone because the particles are extra tiny.  

The really cool part is that this photo was taken on Mars!  Chemical analysis shows that the mudstone formed under fresh water.

'We know that on Mars there was what we interpret to be a habitable environment, where water was good enough for us to drink,' said Melissa Rice, of the California Institute of Technology in Pasadena.

In other words, there was a time when we could have lived on Mars!

Mudstones are good for finding fossils.  The tiny mud particles can show impressions of tiny shells and such.  I would love to get a magnifying lens on that Mars rock!!

More information at NPR.