BH250-34
Title
BH250-34
Subject
Garnet rich immature "sandstone"
Description
Major Minerals: garnet, orthopyroxene
Minor Minerals: plagioclase, chlorite
Sandstone is one of the most common sedimentary rocks and plays a critical role in sedimentary geology, stratigraphy, petroleum geology, and hydrogeology. It is a clastic sedimentary rock composed primarily of sand-sized particles (0.0625 to 2 mm in diameter), cemented together by a matrix of finer particles and/or chemical cement.
The most abundant mineral in sandstone is quartz, valued for its hardness and chemical stability. Feldspars—both plagioclase and K-feldspar—are also common, particularly in arkosic sandstones, although they are less chemically stable than quartz. Sandstones often contain lithic fragments, which are pieces of pre-existing igneous, metamorphic, or sedimentary rocks. Accessory minerals may include micas (muscovite and biotite), zircon, tourmaline, magnetite, and garnet.
The mineralogical composition of sandstone provides essential clues about its provenance. Provenance analysis is a powerful tool in reconstructing sediment transport pathways and inferring tectonic settings.
Cementation and Diagenesis:
Cementation is a diagenetic process whereby minerals precipitate in the pore spaces between grains, binding them together. Common types of cement include:
Silica (cryptocrystalline silica/quartz overgrowths)
Calcite (CaCO₃)
Iron oxides (e.g., hematite, goethite)
Clay minerals, such as Fe-rich illite (glauconite)
Sandstone Classification
Sandstones are classified based on grain composition and matrix content:
By Grain Composition (QFL: Quartz–Feldspar–Lithic Fragments):
Quartz arenite: >90% quartz
Arkose (feldspathic arenite): >25% feldspar
Litharenite: >25% lithic fragments
By Matrix Content:
Arenite: Clean sandstone with <15% matrix
Wacke: Mud-rich sandstone with >15% matrix (e.g., graywacke)
Depositional Environments
Sandstones form in a range of depositional environments, including:
Fluvial
Aeolian
Shoreline/Beach
Deltaic
Deep-marine (e.g., turbidites)
BH250 Sandstone Collection
The BH250 collection includes thirteen sandstone samples collected from southeastern Minnesota and from geology field trips across the Midwest, South Dakota, the Grand Canyon, and Death Valley. Each sample is accompanied by hand specimens, thin sections, and photomicrographs, providing an excellent foundation for detailed petrographic analysis. Here you will find short descriptions for each sandstone sample.
BH250-34 was collected by Bill Dinklage and it has angular fragments of garnet that make up this very immature sedimentary rock which is hard to call is sandstone.
BH250-34 is an exceptionally immature sandstone sample collected by Bill Dinklage. It is dominated by angular garnet grains, along with orthopyroxene, plagioclase, and chlorite, indicating a proximal source area and minimal sedimentary transport. The coarse grain size and angularity of the garnet fragments suggest that this rock borders on a garnet-rich sediment or metamorphic rock that is weathering and delivering these sediments.
This sample represents a highly mineralogically immature clastic rock, lacking the quartz dominance typical of most sandstones. Its composition points to derivation from a high-grade metamorphic or mafic igneous source.
Minor Minerals: plagioclase, chlorite
Sandstone is one of the most common sedimentary rocks and plays a critical role in sedimentary geology, stratigraphy, petroleum geology, and hydrogeology. It is a clastic sedimentary rock composed primarily of sand-sized particles (0.0625 to 2 mm in diameter), cemented together by a matrix of finer particles and/or chemical cement.
The most abundant mineral in sandstone is quartz, valued for its hardness and chemical stability. Feldspars—both plagioclase and K-feldspar—are also common, particularly in arkosic sandstones, although they are less chemically stable than quartz. Sandstones often contain lithic fragments, which are pieces of pre-existing igneous, metamorphic, or sedimentary rocks. Accessory minerals may include micas (muscovite and biotite), zircon, tourmaline, magnetite, and garnet.
The mineralogical composition of sandstone provides essential clues about its provenance. Provenance analysis is a powerful tool in reconstructing sediment transport pathways and inferring tectonic settings.
Cementation and Diagenesis:
Cementation is a diagenetic process whereby minerals precipitate in the pore spaces between grains, binding them together. Common types of cement include:
Silica (cryptocrystalline silica/quartz overgrowths)
Calcite (CaCO₃)
Iron oxides (e.g., hematite, goethite)
Clay minerals, such as Fe-rich illite (glauconite)
Sandstone Classification
Sandstones are classified based on grain composition and matrix content:
By Grain Composition (QFL: Quartz–Feldspar–Lithic Fragments):
Quartz arenite: >90% quartz
Arkose (feldspathic arenite): >25% feldspar
Litharenite: >25% lithic fragments
By Matrix Content:
Arenite: Clean sandstone with <15% matrix
Wacke: Mud-rich sandstone with >15% matrix (e.g., graywacke)
Depositional Environments
Sandstones form in a range of depositional environments, including:
Fluvial
Aeolian
Shoreline/Beach
Deltaic
Deep-marine (e.g., turbidites)
BH250 Sandstone Collection
The BH250 collection includes thirteen sandstone samples collected from southeastern Minnesota and from geology field trips across the Midwest, South Dakota, the Grand Canyon, and Death Valley. Each sample is accompanied by hand specimens, thin sections, and photomicrographs, providing an excellent foundation for detailed petrographic analysis. Here you will find short descriptions for each sandstone sample.
BH250-34 was collected by Bill Dinklage and it has angular fragments of garnet that make up this very immature sedimentary rock which is hard to call is sandstone.
BH250-34 is an exceptionally immature sandstone sample collected by Bill Dinklage. It is dominated by angular garnet grains, along with orthopyroxene, plagioclase, and chlorite, indicating a proximal source area and minimal sedimentary transport. The coarse grain size and angularity of the garnet fragments suggest that this rock borders on a garnet-rich sediment or metamorphic rock that is weathering and delivering these sediments.
This sample represents a highly mineralogically immature clastic rock, lacking the quartz dominance typical of most sandstones. Its composition points to derivation from a high-grade metamorphic or mafic igneous source.
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-34. Housed at Carleton College in Minnesota.
Contributor
Bereket Haileab
Bill Dinklage
Bill Dinklage
Type
Thin section
Relation
Collection
Citation
Bereket Haileab, “BH250-34,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/38.