Rock-butter

Rock-butter, a soft mineral substance found oozing from alum slates, and consisting of alum, alumina, and oxide of iron.

Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)

Rockall * Rockford
Rochdale
Roche, St.
Rochefort, Comte de
Rochelle, La
Rochester
Rochester, John Wilmot, Earl of
Rochet
Rock Island
Rock Temples
Rockall
Rock-butter
Rockford
Rockhampton
Rocking Stones
Rockingham, Charles Watson Wentworth, Marquis of
Rocky Mountains
Rococo
Rocroi
Rodbertus, Johann Karl
Roderic
Roderick Random