There are various igneous intrusions including pegmatite, as well as bands of gneiss and schist. Granite and pegmatite intrusions also worked their way into fissures in the older gneiss. Excavations for the latter project have uncovered pegmatite, feldspar, quartz, biotite, and several metals. Perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye. However, pegmatite localities are only well recorded when economic mineralisation is found. It occurs in greisens, pegmatite, and quartz veins often associated with tin ore deposits. They are planning to carve an open pit mine over pegmatite dikes. If the pegmatite fluid is rich in beryllium, crystals of beryl or chrysoberyl could form. Also mined here in the 19th century was mica, pegmatite, and quartz. The most important sources of sheet mica are pegmatite deposits. In some locations, very coarse-grained pegmatite masses occur with granite. Schorl and lithium-rich tourmalines are usually found in granite and granite pegmatite. Lithium is extracted from primarily two sources&colon; pegmatite crystals and lithium salt from brine pools. The primary source for caesium is pollucite, a mineral from a zoned pegmatite. This was on a base of pegmatite and Yorkshire sandstone.