BH250-177
Title
BH250-177
Subject
Black Vishnu Schist
Description
Major Minerals: hornblende, quartz
The Vishnu Schist is one of the oldest rock units in the Grand Canyon, forming part of the Vishnu Basement Rocks exposed in the Inner Gorge. The term "Black Vishnu Schist" refers specifically to the darker, more mafic-rich variants of the Vishnu Schist. These rocks are Paleoproterozoic in age (~1.75 billion years) and are derived from metamorphism of volcanic protoliths as can be seen from the mineral assemblage. Metamorphism reached the amphibolite facies, producing a rock that is strongly foliated and lineated, with well-developed schistosity.
The Black Vishnu Schist is in direct contact with the overlying Paleozoic sedimentary rocks (Tapeats Sandstone) across the famous Great Unconformity, providing a striking example of this profound geologic boundary in North America. I have taken several photos of this nonconformity, which are available on this website.
The Vishnu Schist is one of the oldest rock units in the Grand Canyon, forming part of the Vishnu Basement Rocks exposed in the Inner Gorge. The term "Black Vishnu Schist" refers specifically to the darker, more mafic-rich variants of the Vishnu Schist. These rocks are Paleoproterozoic in age (~1.75 billion years) and are derived from metamorphism of volcanic protoliths as can be seen from the mineral assemblage. Metamorphism reached the amphibolite facies, producing a rock that is strongly foliated and lineated, with well-developed schistosity.
The Black Vishnu Schist is in direct contact with the overlying Paleozoic sedimentary rocks (Tapeats Sandstone) across the famous Great Unconformity, providing a striking example of this profound geologic boundary in North America. I have taken several photos of this nonconformity, which are available on this website.
Coverage
Location: Lower Section, Grand Canyon, Arizona, USA
Nearby Geographic Feature: Grand Canyon
Nearby Geographic Feature: Grand Canyon
Date
August 2015
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-177. Housed at Carleton College in Minnesota.
Contributor
Bereket Haileab
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-177,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/240.