Minllyn is a slate and slab quarry (nprn 310049) begun in the C19, the most productive phase of which began after the Carlyle Slate & Slab Company was formed in 1872. Work ceased in 1924. The tapering square-section boiler stack is 1.8m square at the base, constructed of mortared rubble. It stands 5m high. The stack stands on a plinth which has a lintelled opening on the S side, facing the engine and boiler house (NPRN527466). The stack leans slightly and some masonry is missing on the NW side.
Recorded as part of RCAHMW Uplands Initiative Project, W B Horton, H&H, 17/12/2012.