Sort:  

My guess is that it once was water captured inside it. :)

It seem like something you would see in a chalk or limestone formation. Yet it seems to be neither.

Coin Marketplace

STEEM 0.21
TRX 0.25
JST 0.039
BTC 95882.33
ETH 3347.19
USDT 1.00
SBD 3.21