BH250-98a, BH250-98b, BH250-98c
Title
BH250-98a, BH250-98b, BH250-98c
Subject
Granite with Basaltic Dike
Description
Major Minerals: plagioclase, biotite
Minor Minerals: chlorite, clinopyroxene
Mineralogy Comments: BH250-98a and BH250-98c show the edges of the dike, while BH250-98b shows the dike's center.
A thin basaltic dike intruded into a granite host rock. Upon emplacement, the dike developed a chilled margin where the hot basaltic melt came into contact with the cooler granite. The flow direction of the melt is preserved along the chilled margin, where the alignment of plagioclase laths records the magma's movement. Toward the center of the dike, this flow fabric becomes indistinct, and grain size increases progressively from the margin inward—reflecting slower cooling rates away from the contact zone.
BH250-98a, 98b and 98c are large-format thin section that spans the entire width of the dike, from one granite contact, through the basaltic interior, to the opposite granite contact.
This rock, both in hand sample and thin section, was used for a class project in one of my introductory geology courses. Students measured grain size variations across the dike and analyzed textural transitions. The paper they produced as part of this assignment is attached at the bottom of the page.
Minor Minerals: chlorite, clinopyroxene
Mineralogy Comments: BH250-98a and BH250-98c show the edges of the dike, while BH250-98b shows the dike's center.
A thin basaltic dike intruded into a granite host rock. Upon emplacement, the dike developed a chilled margin where the hot basaltic melt came into contact with the cooler granite. The flow direction of the melt is preserved along the chilled margin, where the alignment of plagioclase laths records the magma's movement. Toward the center of the dike, this flow fabric becomes indistinct, and grain size increases progressively from the margin inward—reflecting slower cooling rates away from the contact zone.
BH250-98a, 98b and 98c are large-format thin section that spans the entire width of the dike, from one granite contact, through the basaltic interior, to the opposite granite contact.
This rock, both in hand sample and thin section, was used for a class project in one of my introductory geology courses. Students measured grain size variations across the dike and analyzed textural transitions. The paper they produced as part of this assignment is attached at the bottom of the page.
Coverage
Location: Granite Falls, Minnesota, USA
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Samples 98a, 98b, and 98c. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Large thin sections 2-3 inches
Large thin sections 2-3 inches
Relation
Collection
Citation
Bereket Haileab, “BH250-98a, BH250-98b, BH250-98c,” BH250 Mineralogy Teaching Collection, accessed April 24, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/336.