A luncart is a discrete, lens-shaped mass or concretion embedded in a host rock of different composition or hardness. In mining, these hard nodules can present sudden obstacles for cutting machinery when they occur unexpectedly in softer coal or shale seams.
Heard on the job
The continuous miner threw a shower of sparks when the cutting head hit a massive ironstone luncart hidden in the seam.
Related terms
Concretion
A hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles.
Kettle bottom
A heavy, cylindrical fossilized tree stump hidden in a coal mine roof that can fall without warning.
Cauldron bottom
A heavy, bell-shaped mass of rock prone to falling from a coal mine roof.