BH250-175d
Title
BH250-175d
Subject
Basalt
Description
Major Minerals: clinopyroxene, orthopyroxene, plagioclase, brown glass, iddingsite
Minor Mineral: aragonite, oxide
Mineralogy Comments: Aragonite occurs within vesicular cavities.
Sample BH250-175d was collected from Grand Canyon during field trips that I lead for Carleton Alumni trip. The sample exhibits a typical basaltic texture and well-developed hexagonal columnar jointing. Vesicles within the flow are commonly filled with secondary minerals, including aragonite.
Aragonite (CaCO₃) is a carbonate mineral chemically identical to calcite but differing in crystal structure. As a polymorph of calcite, it crystallizes in the orthorhombic system and is optically biaxial negative, with a small 2V angle of ~18°. Its high birefringence produces multiple isochromes around the melatope in conoscopic interference figures. Although aragonite’s birefringence is similar to calcite, the two can be distinguished in thin section by their distinct optical properties.
Photomicrographs of the sample display both the basaltic textures and the vesicle-filling aragonite, including its characteristic optical features. For comparison, see the thin sections and photomicrographs from sample BH250-39, which also contain aragonite.
Basaltic lava flows are widely exposed throughout the Grand Canyon. Some of these flows entered the canyon, temporarily damming the Colorado River while advancing downstream along the river channel. The river eventually breached these natural dams and carved new channels, leaving behind remnants of the lava flows that can be traced up to 120 km downstream. These remnants of the lava flows are now preserved as inverted topography (see photographs of the outcrops).
These lava flows originated from the Uinkaret volcanic field on the North Rim of the Grand Canyon creating natural dams that are estimated to have been over 600 meters (2,000 feet) high.
Another striking example of inverted topography, shared by Frank H. Brown, is located in Kenya at 2°17'42.94"S, 38°11'33.09"E. There, a lava flow erupted from the Kenyan highlands, exploiting an existing river(s) course that flowed toward the Indian Ocean. The lava traveled nearly 800 km along this channel. I plan to collect a sample from this flow in the future to analyze its chemistry and determine the lava type responsible for such an extensive journey.
Minor Mineral: aragonite, oxide
Mineralogy Comments: Aragonite occurs within vesicular cavities.
Sample BH250-175d was collected from Grand Canyon during field trips that I lead for Carleton Alumni trip. The sample exhibits a typical basaltic texture and well-developed hexagonal columnar jointing. Vesicles within the flow are commonly filled with secondary minerals, including aragonite.
Aragonite (CaCO₃) is a carbonate mineral chemically identical to calcite but differing in crystal structure. As a polymorph of calcite, it crystallizes in the orthorhombic system and is optically biaxial negative, with a small 2V angle of ~18°. Its high birefringence produces multiple isochromes around the melatope in conoscopic interference figures. Although aragonite’s birefringence is similar to calcite, the two can be distinguished in thin section by their distinct optical properties.
Photomicrographs of the sample display both the basaltic textures and the vesicle-filling aragonite, including its characteristic optical features. For comparison, see the thin sections and photomicrographs from sample BH250-39, which also contain aragonite.
Basaltic lava flows are widely exposed throughout the Grand Canyon. Some of these flows entered the canyon, temporarily damming the Colorado River while advancing downstream along the river channel. The river eventually breached these natural dams and carved new channels, leaving behind remnants of the lava flows that can be traced up to 120 km downstream. These remnants of the lava flows are now preserved as inverted topography (see photographs of the outcrops).
These lava flows originated from the Uinkaret volcanic field on the North Rim of the Grand Canyon creating natural dams that are estimated to have been over 600 meters (2,000 feet) high.
Another striking example of inverted topography, shared by Frank H. Brown, is located in Kenya at 2°17'42.94"S, 38°11'33.09"E. There, a lava flow erupted from the Kenyan highlands, exploiting an existing river(s) course that flowed toward the Indian Ocean. The lava traveled nearly 800 km along this channel. I plan to collect a sample from this flow in the future to analyze its chemistry and determine the lava type responsible for such an extensive journey.
Coverage
Location: Pumpkin Spring Pool, Grand Canyon, Arizona, USA
Nearby Feature: Grand Canyon
GPS Coordinates: 35°54'58.39"N, 113°20'2.21"W
Nearby Feature: Grand Canyon
GPS Coordinates: 35°54'58.39"N, 113°20'2.21"W
Date
August 2021
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-175d. Housed at Carleton College in Minnesota.
Contributor
Bereket Haileab
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-175d,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/230.