BH250-25
Title
BH250-25
Subject
Staurolite Quartzite
Description
Major Mineral: staurolite
Minor Minerals: muscovite, chlorite
Mineralogy Comments: lots of chlorite
Thin sections of BH250-25 from Petaca reveal a quartz-rich matrix with sparse, euhedral staurolite porphyroblasts and scattered opaque oxides. The rock is composed of interlocking grains of quartz and staurolite, which occurs as brown, high-relief prismatic crystals. The staurolite is strongly pleochroic, showing pale yellow to brown shades in plane polarized light. Minor amounts of magnetite appear as opaque black grains dispersed throughout the section.
Petrologic Significance
The presence of staurolite, an aluminum-rich silicate, in association with quartz has important implications. Staurolite is metamorphic index mineral, forming under intermediate to high grade conditions in pelitic rocks. The original bulk composition was rich in clay minerals.
The presence of both staurolite and quartz indicates a silica-saturated, Al-rich bulk composition, typical of metapelitic protoliths subjected to elevated pressures and temperatures during regional metamorphism.
There are plenty of chlorite (alteration from biotite) in this thin section indicate that the rock is undergoing retrograde metamorphism.
Compare BH250-4, BH250-21, BH250-25 with, BH250-27, 27b, 27c, BH250-160 and BH250-183
Minor Minerals: muscovite, chlorite
Mineralogy Comments: lots of chlorite
Thin sections of BH250-25 from Petaca reveal a quartz-rich matrix with sparse, euhedral staurolite porphyroblasts and scattered opaque oxides. The rock is composed of interlocking grains of quartz and staurolite, which occurs as brown, high-relief prismatic crystals. The staurolite is strongly pleochroic, showing pale yellow to brown shades in plane polarized light. Minor amounts of magnetite appear as opaque black grains dispersed throughout the section.
Petrologic Significance
The presence of staurolite, an aluminum-rich silicate, in association with quartz has important implications. Staurolite is metamorphic index mineral, forming under intermediate to high grade conditions in pelitic rocks. The original bulk composition was rich in clay minerals.
The presence of both staurolite and quartz indicates a silica-saturated, Al-rich bulk composition, typical of metapelitic protoliths subjected to elevated pressures and temperatures during regional metamorphism.
There are plenty of chlorite (alteration from biotite) in this thin section indicate that the rock is undergoing retrograde metamorphism.
Compare BH250-4, BH250-21, BH250-25 with, BH250-27, 27b, 27c, BH250-160 and BH250-183
Coverage
Location: Petaca, New Mexico, USA
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-25. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-25,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/28.