BH250-54
Title
BH250-54
Subject
Siderite–Biotite Vein
Description
Major Minerals: siderite
Minor Minerals: biotite, calcite, chlorite
This vein is dominated by siderite with minor biotite, and likely represents a metamorphosed or hydrothermally altered iron-rich rock, commonly derived from iron-rich sediments (such as ironstones) or carbonate-rich protoliths.
The protolith was likely an iron-rich sedimentary rock (e.g., ironstone or siderite-rich mudstone) or a carbonate-rich rock that underwent hydrothermal alteration.
Siderite has low birefringence, typically gray or colorless in plane-polarized light; commonly euhedral. Sections cut perpendicular to the c-axis yield a centered optic axis, uniaxial negative interference figure with no isochromes.
Biotite has strong pleochroism (brown to dark brown), high relief, moderate birefringence (bird’s-eye maple), with perfect basal cleavage visible in thin section.
These types of rocks typically form in hydrothermal veins, contact metamorphic zones, or metasomatic environments, where iron-rich fluids interact with carbonate-rich protoliths.
Minor Minerals: biotite, calcite, chlorite
This vein is dominated by siderite with minor biotite, and likely represents a metamorphosed or hydrothermally altered iron-rich rock, commonly derived from iron-rich sediments (such as ironstones) or carbonate-rich protoliths.
The protolith was likely an iron-rich sedimentary rock (e.g., ironstone or siderite-rich mudstone) or a carbonate-rich rock that underwent hydrothermal alteration.
Siderite has low birefringence, typically gray or colorless in plane-polarized light; commonly euhedral. Sections cut perpendicular to the c-axis yield a centered optic axis, uniaxial negative interference figure with no isochromes.
Biotite has strong pleochroism (brown to dark brown), high relief, moderate birefringence (bird’s-eye maple), with perfect basal cleavage visible in thin section.
These types of rocks typically form in hydrothermal veins, contact metamorphic zones, or metasomatic environments, where iron-rich fluids interact with carbonate-rich protoliths.
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 54. Housed at Carleton College in Minnesota.
Type
Thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-54,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/63.