BH250-49
Title
BH250-49
Subject
Sacred Heart Granite
Description
Major Minerals: microcline, orthoclase, quartz
Minor Minerals: albite, biotite, muscovite, chlorite (pennite), sphene (titanite), zicon, monazite, oxides
Mineralogy Comments: thin sections contain myrmekite
Alteration: orthoclase and plagicalse are altered to sercite (white mica), biotite to chlorie alteration
BH250-49 is from the Sacred Heart Granite near Belview, Minnesota—one of our regular stops on field trips to the Minnesota River Valley. The Sacred Heart Granite is a Neoarchean pluton that intruded the older Morton and Montevideo gneiss complexes around 2.604 Ga (2,604 million years ago). Recenlty Emma Watson a Carleton College student from the Class of 2023, worked on this rock and obtained revised age determinations for the pluton.
The intrusion represents the final phase of high-grade metamorphic and deformational events that produced the Morton Gneiss and surrounding metamorphic rocks, closely tied to the last stages of Neoarchean convergent tectonics in the region.
BH250-49 is a medium-grained, massive, and typically pink to gray granite, generally fresh and only weakly deformed relative to the surrounding gneisses. Its modal composition is approximately 40% K-feldspar, 30% oligoclase (a plagioclase feldspar), and 25% quartz, with subordinate amounts of biotite.
Minor Minerals: albite, biotite, muscovite, chlorite (pennite), sphene (titanite), zicon, monazite, oxides
Mineralogy Comments: thin sections contain myrmekite
Alteration: orthoclase and plagicalse are altered to sercite (white mica), biotite to chlorie alteration
BH250-49 is from the Sacred Heart Granite near Belview, Minnesota—one of our regular stops on field trips to the Minnesota River Valley. The Sacred Heart Granite is a Neoarchean pluton that intruded the older Morton and Montevideo gneiss complexes around 2.604 Ga (2,604 million years ago). Recenlty Emma Watson a Carleton College student from the Class of 2023, worked on this rock and obtained revised age determinations for the pluton.
The intrusion represents the final phase of high-grade metamorphic and deformational events that produced the Morton Gneiss and surrounding metamorphic rocks, closely tied to the last stages of Neoarchean convergent tectonics in the region.
BH250-49 is a medium-grained, massive, and typically pink to gray granite, generally fresh and only weakly deformed relative to the surrounding gneisses. Its modal composition is approximately 40% K-feldspar, 30% oligoclase (a plagioclase feldspar), and 25% quartz, with subordinate amounts of biotite.
Coverage
Location: near Sacred Heart, Minnesota, USA
GPS Coordinates: 44°39'28.95"N, 95°20'17.19"W
GPS Coordinates: 44°39'28.95"N, 95°20'17.19"W
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-49. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-49,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/57.