BH250-69
Title
BH250-69
Subject
Sandstone
Description
Major Mineral: quartz
Minor Minerals: iron oxide, altered glauconite
Mineralogy Comments: glauconite, iron-oxide and silica overgrowth cement
BH250-69 is a sandstone sample collected from the Little Elk Creek Trail, in South Dakota and belongs to the Deadwood Formation. The Deadwood Sandstone is a well-known geological unit from the Black Hills region of South Dakota and extends into parts of Wyoming and Montana. It is one of the oldest sedimentary formations exposed in the region and plays a significant role in understanding the early Paleozoic geologic history of North America. The formation is Cambrian to Early Ordovician in age and represents one of the earliest marine transgressive sequences on the North American craton following the erosion of the Precambrian basement.
The sandstone is composed primarily of quartz framework grains, which are predominantly well-rounded and mature, including both monocrystalline and polycrystalline varieties. Iron oxide and glauconite act as cementing agents in the formation. These impart a reddish to greenish coloration to some beds.
Glauconite, a hydrated potassium iron silicate, is an authigenic mineral, meaning it forms in place within the sedimentary environment rather than being transported. It typically develops in marine depositional settings characterized by slow sedimentation rates. The mineral often forms within fecal pellets, foraminiferal chambers, or microfossil shells, where reducing conditions driven by the decay of organic matter promote glauconite precipitation.
For more information see, BH250 – Sandstone Overview with Petrographic Notes
Minor Minerals: iron oxide, altered glauconite
Mineralogy Comments: glauconite, iron-oxide and silica overgrowth cement
BH250-69 is a sandstone sample collected from the Little Elk Creek Trail, in South Dakota and belongs to the Deadwood Formation. The Deadwood Sandstone is a well-known geological unit from the Black Hills region of South Dakota and extends into parts of Wyoming and Montana. It is one of the oldest sedimentary formations exposed in the region and plays a significant role in understanding the early Paleozoic geologic history of North America. The formation is Cambrian to Early Ordovician in age and represents one of the earliest marine transgressive sequences on the North American craton following the erosion of the Precambrian basement.
The sandstone is composed primarily of quartz framework grains, which are predominantly well-rounded and mature, including both monocrystalline and polycrystalline varieties. Iron oxide and glauconite act as cementing agents in the formation. These impart a reddish to greenish coloration to some beds.
Glauconite, a hydrated potassium iron silicate, is an authigenic mineral, meaning it forms in place within the sedimentary environment rather than being transported. It typically develops in marine depositional settings characterized by slow sedimentation rates. The mineral often forms within fecal pellets, foraminiferal chambers, or microfossil shells, where reducing conditions driven by the decay of organic matter promote glauconite precipitation.
For more information see, BH250 – Sandstone Overview with Petrographic Notes
Coverage
Location: Lower Black Hills, South Dakota, USA
GPS Coordinates: 44°14'19.19"N, 103°26'23.61"W
GPS Coordinates: 44°14'19.19"N, 103°26'23.61"W
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-69. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-69,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/79.