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Twin Peaks, Lead District, Lawrence Co., South Dakota, USA

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Latitude & Longitude (WGS84): 44° 22' 12'' North , 103° 52' 44'' West
Latitude & Longitude (decimal): 44.37016,-103.87893
GeoHash:G#: 9xyhkjmdv
Locality type:Group of Peaks
Köppen climate type:Dfb : Warm-summer humid continental climate


Porphry 5 miles west of town.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


1 valid mineral.

Detailed Mineral List:

'Hornblende'
Reference: SDSMT Bull 18 Roberts and Rapp "Mineralogy of the Black Hills"
Orthoclase
Formula: K(AlSi3O8)
Reference: SDSMT Bull 18 Roberts and Rapp "Mineralogy of the Black Hills"

List of minerals arranged by Strunz 10th Edition classification

Group 9 - Silicates
'Orthoclase'9.FA.30K(AlSi3O8)
Unclassified Minerals, Rocks, etc.
'Hornblende'-

List of minerals arranged by Dana 8th Edition classification

Group 76 - TECTOSILICATES Al-Si Framework
Al-Si Framework with Al-Si frameworks
Orthoclase76.1.1.1K(AlSi3O8)
Unclassified Minerals, Rocks, etc.
'Hornblende'-

List of minerals for each chemical element

OOxygen
O OrthoclaseK(AlSi3O8)
AlAluminium
Al OrthoclaseK(AlSi3O8)
SiSilicon
Si OrthoclaseK(AlSi3O8)
KPotassium
K OrthoclaseK(AlSi3O8)

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

Eocene - Paleocene
33.9 - 66 Ma



ID: 2474141
Phonolitic intrusive rocks

Age: Paleogene (33.9 - 66 Ma)

Description: Greenish gray, phaneritic. Typically, fresh exposures contrast with weathered intermediate-composition rocks. Forms laccolithic bodies, sills, and dikes.

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]

Eocene - Paleocene
33.9 - 66 Ma



ID: 2749430
Phonolitic Intrusive Rocks

Age: Paleogene (33.9 - 66 Ma)

Description: Gray to greenish-gray sills, laccoliths, and small stocks of phonolite, trachyphonolite, and trachyandesite. Contains phenocrysts of andesine, feldspathoids, aegirine-augite, biotite, and sphene in a finely crystalline plagioclase-biotote-feldsphoid groundmass.

Lithology: Major:{hypabyssal felsic alkaline,hypabyssal trachyte}

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]

Permian - Devonian
251.902 - 419.2 Ma



ID: 3190647
Paleozoic sedimentary rocks

Age: Phanerozoic (251.902 - 419.2 Ma)

Lithology: Sedimentary rocks

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]

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


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