BH250-42
Title
BH250-42
Subject
Amphibolite
Description
Major Mineral: hornblende
Minor Mineral: quartz, plagiocalse
Optics: two cleavages, 60/120 degree cleavages, pleochroic, pleochroism
BH250-42 is an amphibolite, a metamorphic rock predominantly composed of amphibole minerals—mainly hornblende—and quartz. It typically forms through the metamorphism of mafic igneous rocks such as basalt or gabbro, though it can also originate from sedimentary rocks with appropriate composition.
BH250-42 exhibits a foliated texture resulting from the alignment of hornblende crystals and plagioclase feldspar. The grain size ranges from fine to coarse.
Types
Metabasalt-derived amphibolite: formed by metamorphism of basaltic protoliths.
Original Bulk Composition (Protolith)
The protolith of amphibolite is typically a mafic igneous rock, such as basalt or gabbro. The bulk chemistry, especially calcium and magnesium content, strongly influences the mineral assemblage developed during metamorphism, favoring the formation of amphibole minerals.
Minor Mineral: quartz, plagiocalse
Optics: two cleavages, 60/120 degree cleavages, pleochroic, pleochroism
BH250-42 is an amphibolite, a metamorphic rock predominantly composed of amphibole minerals—mainly hornblende—and quartz. It typically forms through the metamorphism of mafic igneous rocks such as basalt or gabbro, though it can also originate from sedimentary rocks with appropriate composition.
BH250-42 exhibits a foliated texture resulting from the alignment of hornblende crystals and plagioclase feldspar. The grain size ranges from fine to coarse.
Types
Metabasalt-derived amphibolite: formed by metamorphism of basaltic protoliths.
Original Bulk Composition (Protolith)
The protolith of amphibolite is typically a mafic igneous rock, such as basalt or gabbro. The bulk chemistry, especially calcium and magnesium content, strongly influences the mineral assemblage developed during metamorphism, favoring the formation of amphibole minerals.
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-42. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-42,” BH250 Mineralogy Teaching Collection, accessed April 24, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/47.