BH250-154
Title
BH250-154
Subject
Jacobsville Sandstone
Description
Major Minerals: quartz, muscovite, orthoclase
Minor Minerals: oxides
Texture: arkosic sandstone, lithic fragment, reduction spot
The Jacobsville Sandstone is a sedimentary rock unit exposed extensively in the Upper Peninsula of Michigan, particularly along the shores of Lake Superior, and forms part of the Midcontinent Rift-related sedimentary sequence. It is notable for its distinctive red color, thick bedding, and broad regional extent.
Mineralogically, the Jacobsville Sandstone is composed predominantly of quartz with angular to subangular grains, forming the dominant framework. It is classified as an arkosic sandstone due to its high feldspar content, including both plagioclase and K-feldspar. Additional components include lithic fragments, muscovite, and hematite, the latter being abundant as both a pigment and a cementing agent. The arkosic composition and the presence of feldspar suggest a short transport distance from the source and/or tectonic uplift, facilitating rapid erosion and deposition.
Reduction Spots
The red color of the sandstone results from oxidized iron (hematite) in the cement. Locally, this coloration is interrupted by pale reduction spots or zones, typically circular or patchy, and appearing greenish or grayish. These spots form from localized reducing fluids, likely introduced during diagenesis or later fluid flow events, which chemically reduce ferric iron (Fe³⁺) in hematite to ferrous iron (Fe²⁺)—a soluble or pale-colored form.
In some cases, organic matter may have contributed to the reduction process. Organic residues can act as reducing agents, leaching iron and producing reduction spots where hematite is altered or removed.
This unit is correlated with the Hinckley Sandstone.
For more information see, BH250 – Sandstone Overview with Petrographic Notes
Minor Minerals: oxides
Texture: arkosic sandstone, lithic fragment, reduction spot
The Jacobsville Sandstone is a sedimentary rock unit exposed extensively in the Upper Peninsula of Michigan, particularly along the shores of Lake Superior, and forms part of the Midcontinent Rift-related sedimentary sequence. It is notable for its distinctive red color, thick bedding, and broad regional extent.
Mineralogically, the Jacobsville Sandstone is composed predominantly of quartz with angular to subangular grains, forming the dominant framework. It is classified as an arkosic sandstone due to its high feldspar content, including both plagioclase and K-feldspar. Additional components include lithic fragments, muscovite, and hematite, the latter being abundant as both a pigment and a cementing agent. The arkosic composition and the presence of feldspar suggest a short transport distance from the source and/or tectonic uplift, facilitating rapid erosion and deposition.
Reduction Spots
The red color of the sandstone results from oxidized iron (hematite) in the cement. Locally, this coloration is interrupted by pale reduction spots or zones, typically circular or patchy, and appearing greenish or grayish. These spots form from localized reducing fluids, likely introduced during diagenesis or later fluid flow events, which chemically reduce ferric iron (Fe³⁺) in hematite to ferrous iron (Fe²⁺)—a soluble or pale-colored form.
In some cases, organic matter may have contributed to the reduction process. Organic residues can act as reducing agents, leaching iron and producing reduction spots where hematite is altered or removed.
This unit is correlated with the Hinckley Sandstone.
For more information see, BH250 – Sandstone Overview with Petrographic Notes
Coverage
GPS Coordinates: 46°35'20.11"N, 87°23'6.18"W
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-154. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-154,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/192.