Mastodon have pressed Marrow Deep into a variant that contains fossilised mastodon teeth, ground to dust and mixed into the vinyl. There are 170 copies, and the number is set by how much dust there was.
The chain of favours behind that is the interesting part. A fan handed the band fossils not good enough to display some twenty years ago, they sat unused, and Troy Sanders decided the album's title made them a record. Loma Vista spent weeks asking pressing plants before Waxworks Records agreed, and the geology department at the University of Georgia did the grinding, because particles too coarse would wreck both the sound and the stylus.
Then the band went to the plant and sprinkled the dust by hand, copy by copy, which is filmed and posted. As a piece of merchandising it is close to perfect: unrepeatable by anyone else, impossible to counterfeit, and it costs the label almost nothing beyond the labour.
Some copies go out through a draw rather than a sale, which is the only fair way to handle 170 units and a resale market that would otherwise take all of them in the first minute.