Lava—a molten rock, especially applied to flows upon the surface, whether from vents or from fissures; also applied to the solidified product.
Lignite (brown coal)—a soft, brown, impure coal.
Limburgite—a compact basic igneous rock of the basaltic class, composed essentially of augite and olivine, with magnetite iron and apatite as common accessories.
Limestone—a rock composed primarily of calcium carbonate, though magnesium sometimes replaces a part of the calcium. (See dolomite and marble.)
Liparite (rhyolite)—an acidic igneous rock of aphanitic or glassy texture, characterized by flowage lines and various microscopic crystals; rhyolite is the more common American name.
Loess—a very fine porous silicious silt containing some calcareous material which often collects in nodules (Löss Kindchen) or in vertical tubules; characterized by a peculiar competency to stand in vertical walls; held by some to be eolian, by others to be fluvial or lacustrine, and by still others to be partly eolian and partly aqueous.
Marble—typically a granular crystalline limestone or dolomite produced by metamorphic action; but the term is variously applied to calcareous and even to other rocks that are colored ornamentally and susceptible of polish.
Marl—an earth formed largely of calcium carbonate, usually derived from the disintegration of shells; or the calcareous accretions of plants, notably the stoneworts; term also sometimes applied to glauconitic and other fertilizing earths.
Melaphyre—a term of varying usage; most commonly applied perhaps to an altered basalt (q.v.), especially an olivine-bearing variety.
Meta-diabase—a term sometimes used for a metamorphic diabase; in like manner meta is prefixed to dolerite, syenite, etc.; not in general use.