Hi folks, Nate & I were on an adventure last weekend, and on the ride back we were discussing nodules, so I took him to a site on the way back where i've encountered some interesting specimens. Can anyone identify? This one in the picture is pretty solidified, but ive discovered ones with space inside, and one with a very fine yellow powder inside which I unfortunately didn't bag & tag for analysis. But yeah, any ideas, not quite a geode...

Perhaps a type of Agate? Pretty dang cool whatever they are. Interesting.

Not sure, Nate had an idea of something involving agragate and rolling waves which might make sense because I think I found a fossilized fin nearby. As I mentioned I found one awhile back, when I cracked it, it looked like the inside cavity was filled with something like powdered sulfur. But what catches my eye is the distinct nodule or geode shape of the outer shell, I'm always keeping my eyes out for strange shaped minerals on my hikes. Might look cool sliced & polished up a bit rather then rough split with a rock hammer as shown, but really no crystalline structure inside, I did find one that had some very small quartz forming inside the shell against the sandy interior. I could probably hollow out the center which i might do and take a picture. Was discovered not too far from Colorado Springs.

Seems like one of the common nodules found around sandstone. I've found a bunch but none of them have had anything too exciting in them... but they do look pretty cool.

It's a concretion. Pretty common in sedimentary rocks. Look up "concretion" or "iron concretion", if you want to know more about the mechanics and theories behind their formation.

Thanks guys and yea GeoMatt is exactly right on ID iron concretions, or concretions. Yes I haven't found anything too cool either Crusty but from what I read you can sometimes find fossils in the center.