Alexandra quarry was a slate quarry in North Wales, on the slopes of Moel Tryfan in north Gwynedd. It was part of one of the major slate quarrying regions of Wales, centred on the Nantlle Valley during the 19th and 20th centuries. Output increased when a connection to the North Wales Narrow Gauge Railways branch to Bryngwyn was created. It closed in the late 1930s, but was subsequently amalgamated with the , and production continued until the 1960s.