Rocks? or something else (West Central IN)

[Theresa]

Hi all.  New member here that grew up collecting small fossils on our farm in southern IN (lots of limestone there).  Now live in west central IN and have the opportunity to collect from a friend's creek where there are geodes to find, other cool rocks and a few fossils.  Not a geologist by any sort but have always loved rock hounding.  

Here are a couple of 'rocks' that I found the other day in the creek and would like to ask opinions on what they are.  I'm assuming just some non-descrip rocks but was wondering if they could possibly be something else.  Sorry, I forgot to include a ruler for scale.  They are sitting on a regular 8.5" x 11" piece of paper in natural sunlight.  The one on the left has a 'clam-like' shape to part of it with some small crystal formations (possibly calcite?) that you really can't see in the photos.  So might be some sort of geode or fossil that turned into a geode?  Size is approximately 2.75" x 2.25" x 2.5".   The one on the right is somewhat 'eggy' in appearance, approximately 2" x 1.5" x 1.75".  Probably a type of rock formation (?) but one never knows, so I'm asking.  
I can get the regular camera out and take closer/higher res photos if necessary.  

TIA.

Theresa

 

[tmaier]

Looks like a chert nodule. This type of stone was very valuable to the native americans for making tools. The stone is very uniform and glassy, and takes a good edge, and is fairly easy to work by fracturing.

Indiana has a lot of good fossils, most from 100's of millions of years ago. Google "Indiana fossils", and then keep you nose to the ground.

[Fossildude19]

Hello, and Welcome to the Forum. 

 

These look like Chert nodules to me. 

Regards, 

 

[Theresa]

Thanks guys!  Yes, chert it would be.  Has the 'marbles' clicking sound.  Took a few more close ups of the 'clam-like' one so that you can see the crystals.

Theresa

[tmaier]

You will also find rocks that are half fossil, and half geological in that area. They are fossils that have been "geodized" by weathering and depositi of minerals. They are usually brachiopods, crinoid stems, and corals. Some people call them "exploded".

http://www.google.com/search?q=indiana+geodized+fossil&btnG=Search&hl=en&gbv=1&tbm=isch

[Theresa]

Thanks for the info!  Yes, it could possibly be what this one is.  If so, it is the biggest brachiopod I've ever found.