I know very little about geology. My sister in Lincoln County. Ky. has been selling geodes on Ebay for years. Her little farm is loaded with them. On the outside they appear to be just rocks but many have crystals inside when cracked open. A lot have hollow spaces inside with loose crystals. She calls these "rattlers." That indicates a hollow space with loose crystals. The crystals vary in color. I would suspect around half are "clear" crystals.  You never know what's inside till they're broken open. No way of telling what color crystals either. I'll post pictures of one before and after being broke open. I can't see good enough to tell much about the innards but they appear to be varying colors. Looks much prettier broken open by my lights. A lady in Kalifornia bought this one, broke it open & sent sis a picture. Interesting.     .......Paul H

Wow that's really cool! When I was a kid in Colorado we used to hunt them and saw them open. I have seen them with Amethyst crystals but they are real pricey! My dad grew up west of Boulder CO and PaPa was a gold and silver minor. Dad was a rock hound and passed it on to my brother and I. Here is a picture of 2 that I found   back in the early 60's. The one on the right is actually petrified wood.

Tell your sister that I LIVE geodes, and would happily purchase some from her!

Paul