BH250-68
Title
BH250-68
Subject
Staurolite Garnet Schist
Description
Major Minerals: biotite, quartz, muscovite
Minor Minerals: graphite, oxides
BH250-68 is a biotite-muscovite schist collected from the Black Hills of South Dakota, similar in origin to BH250-67. However, this sample contains a greater abundance of micas and exhibits exceptionally well-developed foliation, characteristic of regional metamorphism. The well-aligned biotite and muscovite flakes define a prominent schistosity. Compared to BH250-67, the quartz grains in BH250-68 are larger and show striking undulose extinction under cross-polarized light, reflecting a history of dynamic recrystallization. Many of the biotite crystals contain zircon inclusions surrounded by pleochroic halos—classic features observable in thin section. Several quartz grains are ideal for producing uniaxial interference and flash figures, making this a particularly valuable sample for both teaching and research in optical mineralogy and metamorphic petrology.
Minor Minerals: graphite, oxides
BH250-68 is a biotite-muscovite schist collected from the Black Hills of South Dakota, similar in origin to BH250-67. However, this sample contains a greater abundance of micas and exhibits exceptionally well-developed foliation, characteristic of regional metamorphism. The well-aligned biotite and muscovite flakes define a prominent schistosity. Compared to BH250-67, the quartz grains in BH250-68 are larger and show striking undulose extinction under cross-polarized light, reflecting a history of dynamic recrystallization. Many of the biotite crystals contain zircon inclusions surrounded by pleochroic halos—classic features observable in thin section. Several quartz grains are ideal for producing uniaxial interference and flash figures, making this a particularly valuable sample for both teaching and research in optical mineralogy and metamorphic petrology.
Coverage
Location: Black Hills, South Dakota, USA
Date
November 17, 2009
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 68. Housed at Carleton College in Minnesota.
Type
Thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-68,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/78.