Phyllosilicate, palygorskite group
Specific gravity: 2.51
To date (April 2021) windmountainite has been reported only from its type locality, Wind Mountain, Cornudas Mountains, Otero county, New Mexico, USA. Windmountainite is a new mineral species, approved in 2019, and member of the palygorskite group, discovered as orange-brown, radiating aggregates that commonly fill vesicles within a phonolite dike as tightly bound bundles of acicular to bladed crystals.
Associated minerals include albite, aegirine, fluorapophyllite-(K), natrolite, neotocite and montmorillonite, the last of these being observed to replace primary windmountainite.
Windmountainite is considered to have formed from late-stage fluids that were alkaline and oxidised, in conditions reflective of abundant, hydrated feldspathoids (natrolite and analcime) forming as primary rock-forming minerals in the phonolite at Wind Mountain (CM 58.477-509).
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