Nature’s Hand

Curious stones, found locally.

Not ceramic, but intriguing objects and fun to find...

Here in the Albany, NY area, we find these curious stones, most often in creek beds. I find them in the Normanskill, a stream near me where I often canoe.

For years, I've wondered about what they are and how they were formed.  Recently I wrote Dr. Chuck Ver Straeten, Curator of Sedimentary Rocks, New York State Museum, who kindly allowed me to quote his clear explanation:

What you have here are rock objects called “concretions”. You find them is a number of places around the area – places that were flooded and became lakes as the glacial ice melted northward off of NY. In our area, that would be on the order of 15,000 years ago. Ice to the north, and a glacial lake filling the Hudson Valley around here.

Concretions formed down in the lake sediments, below the floor of the lake. In places where some organic material, like a dead fish, a clam, a leaf or a root, or the slime from a worm was buried in the sediment, the decay of the flesh would release ammonia. The ammonia would create a small area around the flesh which had a “basic” (not acidic) chemical composition. This would allow Ca and CO3 in the waters in the sediments to cement the loose sediments together, forming small hard “concretions”, like the ones you found.

As the glacial lake sediments erode away, these concretions come to the surface, where you found them.

Click the images below to enlarge