Post #1180013

@agatesfrommexico@mastodon.social Couldn't tell you in technical terms. I can say that these things form at the bottom of the open ocean over at least 20 years by my reckoning. I think your sulfate theory has legs; they look and also smell like mudflats sediments. As for hardness, they're basically a medium-hard sandstone; you can break them with a hard blow from a claw hammer. After a night in the woodstove they turn dry and crumbly and can be reduced to a coarse powder with moderate pounding. (They turn orange in the kilning and I use the resulting ochre as mortar colour for brick repair.) From that colour change I surmise there's a lot of iron in them, though that might also be because I usually collect pieces formed around steel, which had rusted on the bottom, of course. All in all an interesting topic, the more so since I've found little info about it online.