BH250-186
Title
BH250-186
Subject
Rhyolite
Description
Major Mineral: quartz, plagioclase feldspar, Sanidine with minor mineals such as biotite or hornblende
Minor Mineral: devitrified glass, zircon
BH250-186 is a rhyolite porphyry collected from the northern Minnesota. It represents a geologically significant volcanic rock associated with the Mid-continent Rift System, which formed approximately 1.1 billion years ago.
Rhyolite porphyry is a felsic volcanic rock characterized by phenocrysts (large, well-formed crystals) embedded in a fine-grained to aphanitic groundmass.
The groundmass is rich in microlitic quartz and feldspar, and may exhibit a glassy texture due to rapid cooling.
The rock displays a classic porphyritic texture, with large phenocrysts set in a finer-grained matrix, reflecting a two-stage cooling history, slow crystallization at depth followed by rapid solidification at or near the surface.
Note: There is rhyolite in the Geology collection IA 2.15 (fresh) than the BH250-186 samples
Minor Mineral: devitrified glass, zircon
BH250-186 is a rhyolite porphyry collected from the northern Minnesota. It represents a geologically significant volcanic rock associated with the Mid-continent Rift System, which formed approximately 1.1 billion years ago.
Rhyolite porphyry is a felsic volcanic rock characterized by phenocrysts (large, well-formed crystals) embedded in a fine-grained to aphanitic groundmass.
The groundmass is rich in microlitic quartz and feldspar, and may exhibit a glassy texture due to rapid cooling.
The rock displays a classic porphyritic texture, with large phenocrysts set in a finer-grained matrix, reflecting a two-stage cooling history, slow crystallization at depth followed by rapid solidification at or near the surface.
Note: There is rhyolite in the Geology collection IA 2.15 (fresh) than the BH250-186 samples
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-186. Housed at Carleton College in Minnesota.
Type
Hand sample and thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-186,” BH250 Mineralogy Teaching Collection, accessed April 24, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/233.