BH250-206a
Title
BH250-206a
Subject
Ijolite
Description
Major Minerals: aegirine, aegirine-augite, plagioclase, biotite, nepheline
Minor Mineral: sphene, apatite, chlorite, calcite (secondary)
Optics: In this thin section, biotite displays striking bird’s-eye maple extinction and strong pleochroism. There are biotite grains cut perpendicular to the c-axis are ideal for obtaining centered and off-centered optic axis figures. Sphene (titanite) exhibits extremely high birefringence, producing vivid interference colors. There are well-formed nepheline crystals that provide an excellent teaching example for distinguishing nepheline from quartz. Apatite inclusions within biotite show radiation damage, evidenced by pleochroic halos. Aegirine presents anomalous interference colors.
Minor Mineral: sphene, apatite, chlorite, calcite (secondary)
Optics: In this thin section, biotite displays striking bird’s-eye maple extinction and strong pleochroism. There are biotite grains cut perpendicular to the c-axis are ideal for obtaining centered and off-centered optic axis figures. Sphene (titanite) exhibits extremely high birefringence, producing vivid interference colors. There are well-formed nepheline crystals that provide an excellent teaching example for distinguishing nepheline from quartz. Apatite inclusions within biotite show radiation damage, evidenced by pleochroic halos. Aegirine presents anomalous interference colors.
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-206a. Housed at Carleton College in Minnesota.
Contributor
Bereket Haileab
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-206a,” BH250 Mineralogy Teaching Collection, accessed April 26, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/259.