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Rte. 85A South, Custer, Custer District, Custer Co., South Dakota, USA

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Latitude & Longitude (WGS84): 43° 44' 43'' North , 103° 36' 39'' West
Latitude & Longitude (decimal): 43.74534,-103.61091
GeoHash:G#: 9xy2f78g4
Köppen climate type:Dfb : Warm-summer humid continental climate


One mile south of Custer on both sides of road in granitic pegmatites.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


4 valid minerals.

Detailed Mineral List:

Almandine
Formula: Fe2+3Al2(SiO4)3
Reference: R&M 75:3 pp 156-169
Muscovite
Formula: KAl2(AlSi3O10)(OH)2
Reference: SDSMT Bull 18 Roberts and Rapp "Mineralogy of the Black Hills"
Schorl
Formula: Na(Fe2+3)Al6(Si6O18)(BO3)3(OH)3(OH)
Reference: SDSMT Bull 18 Roberts and Rapp "Mineralogy of the Black Hills"
Spessartine
Formula: Mn2+3Al2(SiO4)3
Reference: R&M 75:3 pp 156-169

List of minerals arranged by Strunz 10th Edition classification

Group 9 - Silicates
'Almandine'9.AD.25Fe2+3Al2(SiO4)3
'Muscovite'9.EC.15KAl2(AlSi3O10)(OH)2
'Schorl'9.CK.05Na(Fe2+3)Al6(Si6O18)(BO3)3(OH)3(OH)
'Spessartine'9.AD.25Mn2+3Al2(SiO4)3

List of minerals arranged by Dana 8th Edition classification

Group 51 - NESOSILICATES Insular SiO4 Groups Only
Insular SiO4 Groups Only with cations in [6] and >[6] coordination
Almandine51.4.3a.2Fe2+3Al2(SiO4)3
Spessartine51.4.3a.3Mn2+3Al2(SiO4)3
Group 61 - CYCLOSILICATES Six-Membered Rings
Six-Membered Rings with borate groups
Schorl61.3.1.10Na(Fe2+3)Al6(Si6O18)(BO3)3(OH)3(OH)
Group 71 - PHYLLOSILICATES Sheets of Six-Membered Rings
Sheets of 6-membered rings with 2:1 layers
Muscovite71.2.2a.1KAl2(AlSi3O10)(OH)2

List of minerals for each chemical element

HHydrogen
H MuscoviteKAl2(AlSi3O10)(OH)2
H SchorlNa(Fe32+)Al6(Si6O18)(BO3)3(OH)3(OH)
BBoron
B SchorlNa(Fe32+)Al6(Si6O18)(BO3)3(OH)3(OH)
OOxygen
O AlmandineFe32+Al2(SiO4)3
O MuscoviteKAl2(AlSi3O10)(OH)2
O SchorlNa(Fe32+)Al6(Si6O18)(BO3)3(OH)3(OH)
O SpessartineMn32+Al2(SiO4)3
NaSodium
Na SchorlNa(Fe32+)Al6(Si6O18)(BO3)3(OH)3(OH)
AlAluminium
Al AlmandineFe32+Al2(SiO4)3
Al MuscoviteKAl2(AlSi3O10)(OH)2
Al SchorlNa(Fe32+)Al6(Si6O18)(BO3)3(OH)3(OH)
Al SpessartineMn32+Al2(SiO4)3
SiSilicon
Si AlmandineFe32+Al2(SiO4)3
Si MuscoviteKAl2(AlSi3O10)(OH)2
Si SchorlNa(Fe32+)Al6(Si6O18)(BO3)3(OH)3(OH)
Si SpessartineMn32+Al2(SiO4)3
KPotassium
K MuscoviteKAl2(AlSi3O10)(OH)2
MnManganese
Mn SpessartineMn32+Al2(SiO4)3
FeIron
Fe AlmandineFe32+Al2(SiO4)3
Fe SchorlNa(Fe32+)Al6(Si6O18)(BO3)3(OH)3(OH)

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Paleoproterozoic
1600 - 2500 Ma



ID: 3191697
Paleoproterozoic crystalline metamorphic rocks

Age: Proterozoic (1600 - 2500 Ma)

Lithology: Paragneiss

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Paleoproterozoic
1600 - 2500 Ma



ID: 2471180
Proximal metagraywacke

Age: Proterozoic (1600 - 2500 Ma)

Description: Light-tan, thick-bedded quartzose schist southwest of Grand Junction fault. Predominantly thick Bouma beds of turbidite deposits. Calc-silicate lenses developed from former concretions. Includes lower and upper part of Bugtown Formation (Redden, 1963). Correlation of Bugtown Formation uncertain due to truncation by Grand Junction fault. Total thickness about 2,200 m.

Reference: Redden, J.A., E. DeWitt. Maps Showing Geology, Structure, and Geophysics of the Central Black Hills, South Dakota. U.S. Geological Survey Scientific Investigations Map 2777. [73]

Paleoproterozoic
1600 - 2500 Ma



ID: 2796248
Lower Metagraywacke

Age: Proterozoic (1600 - 2500 Ma)

Description: Light- to dark-gray, medium- to thick-bedded, quartz-mica schist containing calc-silicate lenses and ellipsoidal masses. Thickness up to 7,000 ft (2,133 m).

Lithology: Major:{schist}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License


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