rheidity
Quick Summary
The term "rheidity" refers to a material's capacity to flow, specifically the time it takes for viscous strain to become 1,000 times greater than elastic strain under a constant shear stress. This concept is a measure of a material's tendency towards fluid-like behavior.1
For example, ice, such as in a glacier, has a rheidity of approximately two weeks. Gypsum flows over about a year, while rock salt, like in a salt dome, takes 10 to 20 years. Serpentine, a mineral, has a rheidity of around 10,000 years, indicating a much more solid-like behavior over shorter timescales.1
The unit of fluidity, the reciprocal of poise, is called a rhe. Rheology is the broader study of how materials flow and deform.21
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