BH250-84
Title
BH250-84
Subject
Phonolite, Orendite, Orendite Wyominite, Lamproite
Description
Major Minerals: leucite
Minor mineral: phlogopite, phengite, phengitic mica
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). This sample is from the geology collection and it is the same as the Leucite Hills that were collected by Cameron Webb, Josh Zoellmer, and Anderson Cole class of 2014! For chemistry and additional photomicrographs see BH250-131s.
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.
Minor mineral: phlogopite, phengite, phengitic mica
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). This sample is from the geology collection and it is the same as the Leucite Hills that were collected by Cameron Webb, Josh Zoellmer, and Anderson Cole class of 2014! For chemistry and additional photomicrographs see BH250-131s.
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
Leucite Hills, Wyoming
Same as BH250-131s
Same as BH250-131s
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-84. Housed at Carleton College in Minnesota.
Type
Thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-84,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/95.