WhatIzIt ???

[Man From Ironbark]

Size: it was weathered or otherwise shrunk to that size. It may well have disappeared entirely since.

Calcium deposit. Well it is calcium that was deposited but that isn't the actual description of the item.


So very warm but not enough to light the cigar.

[Quint]

To be a bit more specific, perhaps a bone or what was once one.

[Man From Ironbark]

Bones are made mostly of collagen, bone is living, growing tissue. Collagen is a protein that provides a soft framework, and calcium phosphate is a mineral that adds strength and hardens the framework. This combination of collagen and calcium makes bone strong and flexible enough to withstand stress. More than 99 percent of the body's calcium is contained in the bones and teeth. The remaining 1 percent is found in the blood.

So not technically a bone but many may call it thus.

There are associated clues in many answers above.
Listed they are:
sand
salt
calcium, though no one has mentioned carbon
bone? not specifically.

Edited to add. I'm afraid that unless you are well travelled, these are absent from Americas.

[Dreamin]

stalagmite or stalactite or coral.

[Luv2shoot]

Frozen water

[Man From Ironbark]

Nope. Unless you have been to beaches outside of the Americas, there's little chance you even know what a cuttle bone looks like.
https://en.wikipedia.org/wiki/Cuttlefish
I couldn't give the answer as bone because it isn't.
Couldn't give the answer as calcium because it isn't.
Cuttlebones are  https://en.wikipedia.org/wiki/Aragonite.

In the case of my photo and this is where you may have seen this item, is that I used to collect these off the beach and put them in the aviary for the budgies to nibble on to strengthen their beaks. As they chew on the cuttlebone, it displays the layers.

       

[Dreamin]

That's weird! I would never have guessed that....so when it deteriorates, it's in layers? Cool.

[Quint]

Quite an interesting Whatizit, MFIB.

Here's one from around here.

[Rich]

Got it...got it!!
The Mummy from the Black Lagoon!!

[Dreamin]