What are these?

[Rubicon]

Found a pile of these about 3 miles back in the woods at an old farm, maybe 50 years since anyones lived there. They remind me of charcoal briquettes, although they are not charcoal. They are similair to plaster in composition and weight. They are also apparently waterproof. Brought 2 back with me just to try to identify. There were both round and triangle shaped in the pile.
Thanks,
Tom in NEPA

 

Amazon Forum Fav 👍

Minelab PRO-FIND 35 Waterproof Pinpointer Metal Detector for Experts with Tone ID & Adjustable Sensitivity - Grab it through Amazon!

[nsdq]

look like fire briks for a propane grill

 

[chrisplay2004]

Ceramic Briquettes are self cleaning and fit all gas grills - replacing dirty lava rocks!
•Durable round Ceramic Briquettes are long lasting.
•Controls flareups!

 

[Bigcypresshunter]

My vote is in for banner.