Figure 9.--Photomicrographs of quartz and other detrital grains, very coarse sand to granule size, Minturn Formation: A) sample 125B, 1824 m below top, Minturn Formation, Eureka Mountain section; B) sample 31M, 665 m below top, Minturn Formation, Marble Mountain section; and C) sample 31J, 1049 m below top, Minturn Formation, Marble Mountain section. (A), (B), and (C), taken under plain polarized light, correspond to (D), (E), and (F), respectively, taken under cross-polarized light. Potassium feldspar stained yellow by cobaltinitrite. Q, monocrystalline quartz; CQ, compound monocrystalline quartz; PQ, polycrystalline quartz (some grains contain metamorphic mica); K, potassium feldspar; P, plagioclase; CP, crushed plagioclase; M, mica (labeled grains are biotite but muscovite also present); GR, granite; and IG, intermediate-composition plutonic rock.