Obsidian
Oceanic Volcanoes
Octahedral Coordination
Oil Field
Oil shale
Old Age
Oolite
Opaque Mineral
Ophiolite Suite
Orbit
Ore
Ore Mineral
Original Horizontality, Principle of
Orogenic Belt
Orogeny
Oscillation Ripple
Outcrop
Outgassing
Outwash
Oxidation
Oxidized Element
Categories: [Geology Terms]