New quest: The Marrowquern (level 45, Alchemy 30, after The Frontier Garden). Marta Cobb at Lampwatch remembers the Quiet Lamp's old field chaplains and the pocket bone mill they carried. Track it through Hearthmoor's ledgers, the Barrow and Dunmar Hold to earn it.
The Marrowquern grinds bones on the go. While it sits in your satchel, bones from your kills become bone meal automatically, with Alchemy XP (a little less than grinding at a table). Left-click it to switch auto-crush on or off.
Crush bones anywhere: right-click the quern or a stack of bones and choose Crush bones. Locked slots are left alone.