Loughlinite with Searlesite

specimen number:
2282010

location:
Westvaco Mine, Sweetwater Co., Wyoming, Usa

description:
Colorless pearly searlesite across matrix with fibrous loughlinite. Good example for both species. Collected in 2023.

The Westvaco mine, located in Sweetwater County, Wyoming, is a massive underground trona mining operation situated within the Green River Basin, which holds the largest known deposit of trona on Earth. Geologically, the deposit formed during the Eocene epoch within ancient Lake Gosiute, where restricted drainage and high evaporation rates led to the deposition of thick, bedded evaporite sequences containing vast quantities of sodium carbonate minerals within the Wilkins Peak Member of the Green River Formation. Industrial interest in the region began following the accidental discovery of trona in a core sample in 1938, and the Westvaco shaft was sunk by the Westvaco Chlorine Products Corporation starting in 1947, marking the birth of the modern commercial Wyoming trona industry. Commercial production commenced in 1948 and has operated continuously for decades under various corporate entities, expanding into a world-class underground room-and-pillar operation that continues to produce millions of tons of natural soda ash annually right through to the present day.

Loughlinite and searlesite are highly specialized authigenic silicate minerals that form as secondary phases within the unique alkaline evaporite environment of the Green River Formation. Geologically, loughlinite is a rare sodium magnesium silicate that crystallizes in the orthorhombic system, typically occurring as fibrous masses or delicate, silky asbestos-like veinlets intimately associated with sepiolite and trona beds, where it forms through the alteration of magnesium-bearing sediments in highly saline, sodium-rich waters. Searlesite is a sodium borosilicate mineral that crystallizes in the monoclinic system, forming thin prismatic crystals, radiating spherulites, or dense granular layers within the oil shales and marlstones surrounding the main trona seams, capturing boron that was concentrated in the ancient lake waters. Both minerals serve as critical indicators of the hyper-alkaline, chemically complex conditions that persisted during the lifecycle of the Eocene lake system, making the Westvaco mine a classic reference locality for saline lacustrine mineralogy.

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