This is a picture of a rail which has failed due to wear and lack of maintenance. The head of the rail has mushroomed from the repeated peening effect of wheels passing over it. Then the mushroomed piece has broken off. You can see the broken piece lying below the rail in the ballast. Those hundred ton cars can really tear up rails and ballast.
This trackage was in great shape during and after WWII, and ran down as the Rock Island ran out of money.
This picture was taken August 8, 2008, at one of my favorite haunts, Bureau Junction, IL. This was a beehive of activity for the old Rock Island railroad until their bankruptcy in 1980, There was even a CTC machine at Bureau controlling two tracks east towards Joliet and west towards Iowa, and a single track south to Peoria.
Iowa Interstate owns this trackage now and still runs trains over it using train orders. The signals and trackside wiring are long since defunct. And one set of tracks has been ripped up.
I located an article discussing preventative rail grinding on the Web. It refers to this kind of failure as "shelling". See: