What is Tufa?
Tufa is a soft, porous rock composed primarily of calcium carbonate (CaCO3) that forms in springs, rivers, and lakes, typically near the Earth’s surface.
How Tufa Forms
Water saturation:
Tuas are created when water that is saturated with dissolved calcium carbonate/calcium bicarbonate ( Ca(HCO3)2) flows over plants, rocks, or other surfaces, causing the dissolved calcium carbonate to precipitate and accumulate as the water releases carbon dioxide.
Carbon dioxide release
As the water flows over the surface, it releases carbon dioxide (CO2) that reacts with calcium carbonate.
Precipitation
The release of CO2 causes a chemical reaction that makes the calcium carbonate precipitate out of the water and solidify into rock.
Accumulation
The calcium carbonate deposits layer by layer, often with the help of plants, algae, and other microorganisms, that get trapped in the rock and contribute to its porous structure.
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- The underlying framework of this unusual formation is a bush that was inundated when the lake flooded. Calcium carbonate precipitated from the lake’s water forming encrustations that grew quickly.
Key conditions
For tufa to form, water is typically oversaturated with calcium carbonate, has a pH greater than 8.0, and contains low levels of dissolved organic matter.
This process often happens at ambient temperatures, resulting in porous formations that may contain remnants of the plants and organisms that helped create them.
How long does it take for tufa to form
Tufa formation rates vary considerably depending on environmental conditions. Read more.
Characteristics and uses
Appearance
It is a soft, creamy-coloured, and often porous rock that may contain fossils of plants, shells, and/or other organisms.
Related Rocks
Tufa is a type of limestone. A similar deposit formed by geothermally heated springs is called travertine.
Use in Jewelry
The porous rock is widely used in a jewelry-making technique called tufa casting, which is a traditional method used by some Native American jewellers.
Classification
The various types of tufa are classified according to their morphology.
Use in Construction
Because tufa is a soft, porous rock, it has been used for construction in various regions, such as the Loire Valley in France.
Important Distinction
Tufa should not be confused with tuff, a volcanic rock made of ash and rock fragments.
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