Tulemite

Tulemite is a carbonate mound or cone that forms when calcium carbonate precipitates around a spring vent on the bottom of a lake or other standing body of water. The structure typically develops as mineral-rich groundwater discharges into the lake, carbon dioxide degasses from the water, and calcite or aragonite precipitates around the vent, building a cone-shaped mound that may include a central hollow or channel.

Formation and morphology: Tulemites grow at or below the water surface around submerged springs. They are composed mainly of calcium carbonate minerals and can display layered textures. Sizes range from a few tens of centimeters to several meters tall, and they often have rough, irregular surfaces with a preserved central opening or shaft where water once emerged.

Distribution and age: The best-known occurrences are in California’s Mono Basin, where carbonate springs on the lake floor have produced numerous tulemites. Similar carbonate spring mounds occur in other parts of the western United States in settings of former or active saline or alkaline lakes with carbonate-rich groundwater. Most tulemites formed during late Quaternary lake episodes, although individual vents may have persisted into more recent times in some locales.

Significance: Tulemites provide insights into past groundwater discharge, lake chemistry, and hydrologic changes in closed-basin settings. As fossil and active features, they help reconstruct paleoenvironmental conditions and lake levels. They are distinct from tufa towers formed along shorelines, as tulemites primarily grow around submerged springs within a lake rather than at the shoreline.