Geology

Back in 1965 or 1966 while looking for geodes in northeast Missouri, I noticed a small black object glistening in the water in the Fox River.  Thinking I had found a really shiny pebble, I reached into the water only to find that it was much larger than I had originally thought.  After digging it out of the mud, cleaning it off, and looking unsuccessfully for others like it, I realized I had found something unusual.

It was about 10″ long and and 4″ in diameter.  It had “flutes” equally spaced at about 30 degree intervals and about 3/4″ tall.  It looked like diorite or some other had black rock, though it was a dull black when dry and not smooth and polished like volcanic rock.  The ends were smoother than the rest of the rock surface and looked like they were sawed and polished, with the edges of these “sawed” surfaces perfectly rounded.  There were 3/8″ holes exactly centered at each end that appeared to reach about 1/4″ into the core (I never tried to dig into them.)  Remembering my  recent science classes, I suspected my rock would exhibit conchoidal fracture if struck.  It rang when lightly struck with another hard object.  There were no broken or chipped edges anywhere on the stone.

Physically it looked like a section of some ancient column, except the “flutes” would never have been cut this deep or perhaps a petrified chunk of some young Jurassic tree.   

The best way to describe this stone would be “a 10″ wide 4″ diameter stone gear,” because that is exactly what it looked like.  I no longer have the rock, so I can’t send a picture. 

Do you have any idea what I might have had?