BH250-5
Title
BH250-5
Subject
Talc Chlorite Schist
Description
Major Minerals: talc, chlorite
Minor Minerals: calcite
BH250-5 is a talc–chlorite schist, a low- to medium-grade metamorphic rock characterized by a strong foliation and a distinctive soapy texture. The dominant minerals are talc and chlorite. Under the microscope, talc exhibits high birefringence, chlorite shows low birefringence, and accessory calcite grains display extremely high birefringence. This sample is excellent for comparing different types of birefringence in minerals under thin section.
Calcite occurs as an accessory phase in irregular patches, grains, or veinlets, frequently intergrown with talc and chlorite. The rock is fine- to medium-grained, with minerals aligned perpendicular to the direction of compression, consistent with regional metamorphism.
The protolith was likely an ultramafic rock such as serpentinite, the metamorphic assemblage indicates low- to medium-grade conditions, typical of the greenschist facies, possibly influenced by contact metamorphism or talc-carbonation reactions. The formation of chlorite suggests a prolonged retrograde metamorphic overprint, especially related to alteration of mafic minerals.
Minor Minerals: calcite
BH250-5 is a talc–chlorite schist, a low- to medium-grade metamorphic rock characterized by a strong foliation and a distinctive soapy texture. The dominant minerals are talc and chlorite. Under the microscope, talc exhibits high birefringence, chlorite shows low birefringence, and accessory calcite grains display extremely high birefringence. This sample is excellent for comparing different types of birefringence in minerals under thin section.
Calcite occurs as an accessory phase in irregular patches, grains, or veinlets, frequently intergrown with talc and chlorite. The rock is fine- to medium-grained, with minerals aligned perpendicular to the direction of compression, consistent with regional metamorphism.
The protolith was likely an ultramafic rock such as serpentinite, the metamorphic assemblage indicates low- to medium-grade conditions, typical of the greenschist facies, possibly influenced by contact metamorphism or talc-carbonation reactions. The formation of chlorite suggests a prolonged retrograde metamorphic overprint, especially related to alteration of mafic minerals.
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 5. Housed at Carleton College in Minnesota.
Type
Thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-5,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/5.