Dacite (quartz-andesite)—an andesite (q.v.) with quartz.
Diabase—a dolerite (q.v.) which has undergone alteration; consists essentially of plagioclase feldspar and augite, with magnetite or titaniferous iron as a common accessory; one of the greenstones.
Diatom ooze—a soft silicious deposit found on the bottom of the deep sea, made largely or partly of the shells of diatoms; similar deposits are formed from the shells of radiolaria.
Diorite—an igneous rock usually of dark-greenish color, consisting of plagioclase feldspar and hornblende; often speckled from the commingling of light feldspar and dark hornblende.
Dolerite—a fine-grained igneous rock composed of plagioclase feldspar (labradorite or anorthite) and augite (or related ferromagnesian mineral, as enstatite, olivine, or biotite), with magnetic or titaniferous iron as common accessories; crystals usually of medium size, assuming the ophitic structure; embraces many of the greenstones; graduates into basalt on the one hand and gabbro on the other.
Dolomite—a magnesian limestone.
Drift—in common American usage, a mixture of clay, sand, gravel, and bowlders formed by glacial agencies.
Eolian rocks—deposits formed by wind, embracing especially dunes and one variety of loess.
Felsite (felstone)—a light-colored aphanitic rock composed of feldspar often with quartz, in which the crystallization is very imperfect or obscure, giving a close-grained texture with conchoidal fracture and flinty aspect; certain varieties are called petrosilex and hälleflinta.
Flint—a compact dark chalcedonic or lithoid form of quartz.