BH250-187b
Title
BH250-187b
Subject
Basalt (North Shore Basalt from Taylors Falls, Minnesota)
Description
Major Minerals: plagioclase, clinopyroxene, iron oxides
BH250-187b is a basalt sample exposed at Taylors Falls, part of the North Shore Volcanic Group (NSVG)—a thick sequence of volcanic rocks formed during the Midcontinent Rift event, a major rifting episode that took place approximately 1.1 billion years ago during the Mesoproterozoic Era. This sample shows coarser phenocryst than BH250-187.
Major minerals include: Plagioclase feldspar, Clinopyroxene (commonly augite), Orthopyroxene (commonly enstatite)
These basalts typically exhibit ophitic to intergranular textures, where plagioclase laths are enclosed by or intergrown with pyroxenes.
Geochemically, this basalt plots in the tholeiitic field characterized by low alkali content and relatively high concentrations of iron and magnesium.
Lava flows in the area range from massive to vesicular, often showing amygdaloidal textures, where gas vesicles have been filled with secondary minerals such as quartz or calcite.
The basalt is well-exposed in Interstate State Park, where it forms the bedrock beneath a landscape shaped by Quaternary glaciations, including dramatic glacial potholes. Some flow layers show flow banding, vesicle-rich zones, and oxidized tops, indicating subaerial eruption and weathering between flow events.
BH250-187b is a basalt sample exposed at Taylors Falls, part of the North Shore Volcanic Group (NSVG)—a thick sequence of volcanic rocks formed during the Midcontinent Rift event, a major rifting episode that took place approximately 1.1 billion years ago during the Mesoproterozoic Era. This sample shows coarser phenocryst than BH250-187.
Major minerals include: Plagioclase feldspar, Clinopyroxene (commonly augite), Orthopyroxene (commonly enstatite)
These basalts typically exhibit ophitic to intergranular textures, where plagioclase laths are enclosed by or intergrown with pyroxenes.
Geochemically, this basalt plots in the tholeiitic field characterized by low alkali content and relatively high concentrations of iron and magnesium.
Lava flows in the area range from massive to vesicular, often showing amygdaloidal textures, where gas vesicles have been filled with secondary minerals such as quartz or calcite.
The basalt is well-exposed in Interstate State Park, where it forms the bedrock beneath a landscape shaped by Quaternary glaciations, including dramatic glacial potholes. Some flow layers show flow banding, vesicle-rich zones, and oxidized tops, indicating subaerial eruption and weathering between flow events.
Coverage
Location: Taylors Falls, Minnesota, USA
Nearby Geographic Features: St. Croix River
GPS Coordinates: 45°23'58.01"N, 92°39'5.89"W
Nearby Geographic Features: St. Croix River
GPS Coordinates: 45°23'58.01"N, 92°39'5.89"W
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-187b. Housed at Carleton College in Minnesota.
Type
Hand sample and thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-187b,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/237.