BH250-121
Title
BH250-121
Subject
Garnet Staurolite Schist
Description
BH250-121 was collected near the Ingersoll Mine, Keystone, South Dakota, USA. This sample represents one of the most beautiful rocks—both in hand sample and thin section. It is a classic example of garnet-staurolite schist from the Black Hills region. The protolith is pelitic shale or graywacke, indicated by the presence of aluminum-rich minerals formed during metamorphism.
Mineral assemblage includes:
Garnet – euhedral to subhedral, commonly poikiloblastic
Staurolite – typically twinned and yellow-brown in color, characteristic of amphibolite facies
Muscovite, biotite, quartz, and plagioclase – all common matrix minerals
Textural features:
Schistosity is well-developed, with micas aligned in a distinct foliation
Porphyroblasts of garnet and staurolite prominently stand out against the fine-grained groundmass, offering excellent contrast in both hand sample and thin section.
This sample is not only geologically significant but also visually striking, making it an outstanding teaching specimen for regional metamorphism and mineral identification. There is a large rock sample in the back of the class room.
Mineral assemblage includes:
Garnet – euhedral to subhedral, commonly poikiloblastic
Staurolite – typically twinned and yellow-brown in color, characteristic of amphibolite facies
Muscovite, biotite, quartz, and plagioclase – all common matrix minerals
Textural features:
Schistosity is well-developed, with micas aligned in a distinct foliation
Porphyroblasts of garnet and staurolite prominently stand out against the fine-grained groundmass, offering excellent contrast in both hand sample and thin section.
This sample is not only geologically significant but also visually striking, making it an outstanding teaching specimen for regional metamorphism and mineral identification. There is a large rock sample in the back of the class room.
Coverage
GPS Location: 43°54'11.77"N, 103°27'2.31"W
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 121. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-121,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/142.