The Dudley pegmatite, located 10.5 km south-east of Penneshaw, was worked during the 1890s and early 1900s for gem tourmaline, ceramic-grade feldspar and silica, and kaolin for brickmaking. The pegmatite outcrop strikes in a north-easterly direction for 550 m, is up to 80 m wide, and varies in appearance and mineralogy from a coarse-grained, perthitic microcline feldspar-quartz-muscovite rock to graphic granite and aplite, often with accessory tourmaline and rare traces of garnet. Gem quality tourmaline, mostly blue and green-coloured, is associated with coarse muscovite and/or quartz crystals in pods and veins that are often elongated parallel to the strike of the pegmatite body. Kaolin occurrences derived from weathered parts of the pegmatite are restricted and of poor guality. Further investigation of possible markets for the Dudley feldspar and silica minerals is recommended, as is the carrying out of more backhoe trenching to look for gem tourmaline zones.