Created by smashing medium stones with a sledgehammer. Repeated hits will shatter a medium stone into ever-smaller fragments (cracked stones, broken stones, split stones, smashed stones), and finally into gravel. The amount of gravel produced by one medium stone is highly variable, anywhere from around 30 to over 100.
Gravel is used, along with with cement, to make concrete in a Clinker Vat.
Each time you smash a stone (either a medium stone or one of its smaller fragments), one of two things can happen:
Odds are roughly equal for either result. The "next smaller stone" for smashed stones is a 'pile' of 1-3 gravel. That is, a smashed stone could turn into 3 piles of 3 gravel. All of the stones sizes above gravel weigh 10 db and are 1 db bulk.
A medium stone becomes a few cracked stones. A cracked stone becomes a few broken stones. A broken stone becomes a few split stones. A split stone becomes a few smashed stones. A smashed stone becomes a few db of gravel.
('a few' in this case is typically 1 to 3)
A smash of any stone may also produce some gravel when producing a smaller stone.
in smashing 20 of each size of stone (except "smashed"), the number of gravel I got was always equal to the number of stones that were not reduced in size. (For smashed stones, the number of gravel at my feet equaled the number of smashed stones collected.) - Sabt-Pestnu
In smashing 2 medium stones, I got 72 gravel from the first and 103 from the second. (OldJoe)
It has been reported that 1 medium stone makes 10 gravel.