BH250-97
Title
BH250-97
Subject
Granite with Basaltic Dike
Description
Major Minerals: plagioclase, clinopyroxene, quartz, biotite
Minor Mineral: penninite
Alteration: biotite to chlorite
A thin basaltic dike intruded into a granite host rock and was later offset by faulting, resulting in visible displacement. Upon intrusion, the dike developed a chilled margin where the basaltic melt came into contact with the cooler granite. The flow direction of the basaltic melt during emplacement is evident along the chilled margin, where the alignment of plagioclase laths records the movement of the magma. Toward the center of the dike, the flow fabric is no longer discernible, and the grain size increases gradually from the margin inward, reflecting slower cooling rates away from the contact zone.
Hand sample and thin section of this rock were used for a class project in one of my introductory geology courses. Students measured the variation in grain size across the dike and analyzed the textural transitions. The paper they produced from this assignment is attached at the bottom of this page.
Minor Mineral: penninite
Alteration: biotite to chlorite
A thin basaltic dike intruded into a granite host rock and was later offset by faulting, resulting in visible displacement. Upon intrusion, the dike developed a chilled margin where the basaltic melt came into contact with the cooler granite. The flow direction of the basaltic melt during emplacement is evident along the chilled margin, where the alignment of plagioclase laths records the movement of the magma. Toward the center of the dike, the flow fabric is no longer discernible, and the grain size increases gradually from the margin inward, reflecting slower cooling rates away from the contact zone.
Hand sample and thin section of this rock were used for a class project in one of my introductory geology courses. Students measured the variation in grain size across the dike and analyzed the textural transitions. The paper they produced from this assignment is attached at the bottom of this page.
Coverage
Location: Granite Falls, Minnesota, USA
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-97. Housed at Carleton College in Minnesota.
Contributor
Bereket Haileab
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-97,” BH250 Mineralogy Teaching Collection, accessed April 26, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/110.