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Here are two links to posts dealing with how to post pictures on Black River Fossils forums.
1. How to Post Pictures on Black River Fossils Forums by ditchweezil
2. How to Post Pictures on Black River Fossils Forums by Daryl
What exactly causes what many folks term "hydration cracks" on various fossil shark teeth, most notably on the enamel surface of Megalodons etc. Hydration to me implies that something is being hydrated or moist with water. Dehydrated means the removal or absence of moisture/water. So, am I missing something in the concept of hydration? I always figured that the cracks either came from the expansion of the material on the inside of the tooth (under the enamel - dentin?), or perhaps from the shrinking of the material on the inside as it fossilized. However, this wouldn't explain why many roots on Megs also exhibit deep cracks. The cracks on the roots are horizontal along the root, whereas the "hydration cracks" on the rest of the tooth run longitudinally up and down the face of the enamel, starting somewhere in the vicinity of the bourlette. Also, why does the display side of the tooth (labial side) usually have more of these cracks than the reverse side?
Any ideas?
Daryl.
I decided to google "hydration cracks"...here's what I found on a website discussing the characteristics of concrete:
Q: Why does concrete crack? Why are joints necessary?
A: There are two types of concrete: concrete that is cracked and concrete that has the potential to crack. When exposed to wetting and drying conditions concrete will expand and contract (similar to a sponge). If the stress associated with these volume changes exceeds the tensile capacity of the concrete, a crack will form. This specific type of crack is referred to as a shrinkage crack. Cracks are expected to form in concrete and act as a "pressure release valve". By intentionally jointing concrete, you decrease the thickness of the slab in that location. This allows a crack to form along a straight line within the joint since the thin section provides a path with less resistance than a thicker section.
So, since the inside of the teeth seem to be similar to concrete (or a concretion like material), perhpas the cracks in the enamel are formed similar to the description above, referred to as a shrinkage crack?