I’ve had some queries on geodes in southeastern Minnesota – YES! The Mississippi River valley is noted for its limestone formations which are the place to hunt geodes in southern Minnesota. These will be sedimentary geodes usually containing calcite or quartz. Up in northeastern Minnesota (The shore of Lake Superior and the quarries thereabout.)you will find volcanic geodes often with an amethyst center – very beautiful.

I would strongly suggest you do a bit of reading at the Wiki site: http://en.wikipedia.org/wiki/Geode

And this site has some wonderful pictures and information on concretions (The base of geodes.) as you read down: http://www.rocksforkids.com/R&M/geodes.html

I am a fossil hunter, but I love anything that sparkles! When I first picked these rocks up, I really had not idea they were fossils, but they sparkled so I dragged them home. It turns out they are geodized cephalopods! How cool is that!

Geodized Cephalopods

A group of geodized cephalopods.

Geodized Cephalopod 1

Note the rounded end.

Geodized Cephalopod 2

Geodized Cephalopod 3

Geodized Cephalopod 4

Geodized cephalopods are not common, but they obviously aren’t uncommon. I have a broken geode, or geodized fossil (Can’t tell because it is in the rock.) in my retaining wall. And I saw a huge geodized cephalopod in a rock in a quarry last year – but the rock was probably a ton. These were all found in Fillmore County in the Galena Formation.

I truly wish I could catch the sparkle with my camera, but alas you will just have to imagine it.  😀