Ultramafic rock but there are ultrapotassic and highly silica-under-saturated rocks with >18% MgO which can be considered "ultramafic". Ultrapotassic, ultramafic igneous rocks such as lamprophyre, lamproite and kimberlite are known to have reached the surface of the Earth. Although no modern eruptions have been observed, analogues are preserved. Most of these rocks occur as dikes, diatremes, lopoliths or laccoliths, and very rarely, intrusions. Most kimberlite and lamproite occurrences occur as volcanic and subvolcanic diatremes and maars; lavas are virtually unknown. Vents of Proterozoic lamproite (Argyle diamond mine), and Cenozoic lamproite (Gaussberg, Antarctica) are known, as are vents of Devonian lamprophyre (Scotland). Kimberlite
Lemei Rock around Lemei Rock include the Indian Heaven Wilderness, which is known for the high mountain meadows among its scattered volcanic peaks. The Pacific Crest National Scenic Trail passes north/south through the volcanic field and the Indian Heaven Wilderness, which is known for its lakes and views of four nearby volcanoes: Mount Adams, Mount Hood, Mount St. Helens, and Mount Rainier. Major trails at Lemei Rock are the Lemei Trail, which climbs up the east side of Lemei Rock; and Wapiki Trail, which descends from the Lemei Trail to the deep blue Wapiki Lake, the "crater lake" of Lemei Rock. The