Meteoric iron is a wonderful substance. Many cultures used it (such as the Egyptians and Inuit) as a source of iron before extracting iron from ore was invented.
It is naturally very hard, keeps a good edge, and is resistant to tarnish. It is also very expensive although surprisingly affordable in small quantities. Go ebay!
It is mostly composed of two different alloys of iron and nickel: kamacite and taenite.http://en.wikipedia.org/wiki/Meteoric_iron
The crystals of these alloys have differential resistances to acid. As a result, you can etch an iron meteorite with a strong acid to make the crystal structure visible.
This process is fairly well documented on youtube, which is where I researched my technique.