BH250-131e
Title
Subject
Description
Minor Minerals: apatite, diopside, orthoclase
Leucite Hills, Wyoming is a geologically fascinating area situated within the Rock Springs Uplift of southwestern Wyoming. It is renowned for its rare, leucite-rich volcanic rocks. These rocks are composed predominantly of ultrapotassic volcanic lithologies, including leucitite a rock characterized by fine-grained to porphyritic textures and abundant leucite (KAlSi₂O₆). The samples from Leucite Hills were collected by Cameron Webb, Josh Zoellmer, and Anderson Cole class of 2014! Thank you, guys!
Petrology and mineralogy:
Leucite is the dominant feldspathoid mineral, commonly forming euhedral phenocrysts as well as fine grains within the groundmass.
Phlogopite, a Ti-rich variety of mica, is widespread in some samples and appears as both groundmass flakes and phenocrysts.
Nepheline occurs occasionally as an accessory feldspathoid mineral.
Geochemistry:
The rocks are ultrapotassic, with K₂O contents often exceeding 10 wt% (see tables in chemical analysis) and plot in the phonolite field on the TAS diagram. They are rich in alkali oxides (Na₂O + K₂O) and display elevated concentrations of Large Ion Lithophile Elements (LILE) such as K, Rb, and Ba as seen in the spider diagram/Rare Earth Plot.
Mica Types:
The primary micas found in Leucite Hills volcanic rocks are, phlogopite, including Ti-rich varieties, which are compositionally distinct. These micas occur as well-formed phenocrysts (up to several millimeters in size) and are mineralogically and chemically significant indicators of mantle metasomatism and magmatic conditions.
Coverage
Nearby Geographic Feature: Zirkel Mesa
GPS Coordinates: 41.7999068, -108.9228398
Creator
Source
Contributor
Cameron Webb '14, Josh Zoellmer '14, and Anderson Cole '14