Lode. A rock mass, often a [vein], containing valuable minerals.
Massif. A mountainous mass that has relatively uniform geologic characteristics and which may embrace a number of peaks.
Mesa. A flat-topped mountain bounded on at least one side by a steep cliff.
Metamorphic rock. Rock formed by alteration of pre-existing rock, especially by great temperatures and pressures.
Mollusk. Any one of the large group of invertebrate animals which includes the snails, clams, octopuses, squids, and their extinct relatives.
Molybdenite. A soft bluish gray, metallic mineral (MoS₂) that is a major ore of molybdenum.
Monocline. A steplike [fold] in otherwise horizontal or gently dipping rock layers.
Moraine. An accumulation of unsorted rock material built up by the action of [glacier] ice.
Native gold. Gold occurring in nature uncombined with other elements.
Peneplain. A land surface worn down by erosion to a nearly flat or broadly undulating plain.