BH250-86
Title
BH250-86
Subject
Bearpaw Green Porphyry
Description
BH250-86 and BH250-86b are from The Bearpaw Green Porphyry and have very interesting mineralogy.
Major Minerals:
Nepheline – a feldspathoid indicating a silica-undersaturated system.
Aegirine – a sodium-rich clinopyroxene found in peralkaline rocks.
Riebeckite – a sodic amphibole, further confirming peralkaline chemistry.
Pseudo-leucite – alteration texture of former leucite, typically to nepheline + alkali feldspar, suggesting originally potassic, high-temperature conditions.
This mineral assemblage is typical of peralkaline to slightly metaluminous phonolites formed in evolved magmatic systems.
Coverage
Location: Bearpaw Mountains, Montana, USA
Nearby Geographic Feature: Bearpaw Mountains
Nearby Geographic Feature: Bearpaw Mountains
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 86. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-86,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/97.