concretion
hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles
septaria
desiccation nodules formed in carbonate-rich mudrock
Loess doll
Clumps caused by carbonate aggregation found in loess
stalagmite
elongated mineral formation which forms on a cave floor
manganese nodule
rock concretion on the sea bottom made of layers of iron/manganese hydroxides