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Iowa, USA

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Geological Map of Iowa (1907)

Iowa, USA
Railroad Cut (1917 or earlier)

Fayette, Fayette Co., Iowa, USA
Geological Map of Iowa (1907)

Iowa, USA
Railroad Cut (1917 or earlier)

Fayette, Fayette Co., Iowa, USA
Geological Map of Iowa (1907)

Iowa, USA
 
Location is approximate, based on center of defined region.
 
Latitude & Longitude: 41° North , 92° West (est.)
Neighbouring regions:
Museums in region:


Iowa is best known for its excellent geodes from the Keokuk area and also for calcite and baryte crystals from abundant carbonate sedimentary rocks exposed throughout the state. These rocks can also provide excellent fossil collecting from road cuts and quarries.

Iowa’s exposed bedrock is little deformed sedimentary rock, dominantly of Paleozoic age. These dip southwest at a gentle angle, meaning that one encounters younger rock as one goes south and west though the state. A blanket of Mesozoic strata overlies these older rocks in the northwest.

Except for isolated exposures of quartzite in the extreme northwestern corner of the state, Precambrian rocks are known only from deep drill cores, which have sampled gneiss, granitic and gabbroic rocks. One of these cores, from Sioux County, is the type locality for iowaite, a blue chlorine-bearing hydroxide. This is found in veins cutting serpentinite.

Cambrian rocks, mainly sandstone, are exposed in the northeast corner of the state notably along the Mississippi River. Ordovician to Mississippian limestones and dolostones deposited in shallow seas are abundant throughout much of the rest of the state. They are often quarried. Some quarries, such as Pint’s Quarry near Raymond, Black Hawk County, or the Conklin Quarry near Coralville in Johnson County yield attractive well-crystallized specimens of calcite, baryte, dolomite, fluorite, millerite and other minerals. Sphalerite, galena and smithsonite have been mined, primarily from Ordovician strata, in the Dubuque area, which is part of the Upper Mississippi Valley zinc-lead district. High purity limestone of Devonian age is mined underground in the Linwood Mine in Scott County. This has produced wonderful calcite and baryte crystal clusters. Some Mississippian strata contains significant gypsum deposits which have been mined, notably near Sperry in Des Moines County. The Mississippian formations also are the home of the world-famous quartz geodes of the Keokuk area, and adjacent Illinois and Missouri. The geodes are best dug from fee sites, but can also be collected loose where they weather out and concentrate in stream beds. In addition to quartz, many other minerals, such calcite, sphalerite, dolomite and millerite can be found in the geodes.

Younger Pennsylvanian strata cover much of the southwestern quarter of the state. They consist of sandstone, coal and shale deposited in low-lying alluvial plains and adjacent shallow seas. The coal has been mined in the past, but its relatively high sulfur content has made it presently undesirable. The old mines, such as those near Oskaloosa in Mahaska County, have yielded baryte, calcite, pyrite, marcasite and other minerals.

Some scattered Jurassic rocks in the Fort Dodge area have high-quality gypsum and anhydrite beds, which are mined. The northwestern part of the state is covered by Cretaceous sediments. The early Cretaceous materials are non-marine sandstone and clay that include some limonitic iron ore at the base. This ore was mined in Allamakee County. The late Cretaceous rocks are primarily calcareous shales. These can provide some interesting vertebrate and invertebrate fossils.

A major Cretaceous impact site occurs in the subsurface near Manson, Pocahontas County, Iowa. This crater formed about 74 million years ago, and has a diameter of 23 miles. It is unfortunately entirely covered by younger strata. Another probable impact site, this of Ordovician age, has recently been described in the Dubuque area. Also of extraterrestrial note, Iowa is indirectly the type locality for stanfieldite and tetrataenite, which were first noted in the Estherville meteorite that fell in Emmet County.

Glacial and alluvial deposits are widespread in the state. Glacially transported Lake Superior agates, gold, iron formation, float copper and, rarely, a diamond or two can be found by careful searching in this material.


Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.


Mineral List

Mineral list contains entries from the region specified including sub-localities

'Albite-Anorthite Series'

Analcime

Andradite

Anglesite

Anhydrite

Ankerite

Anorthite

var: Bytownite

'Antitaenite'

'Apatite'

Aragonite

var: Aragonite Satin Spar

Augite

Azurite

Baryte

'Bitumen'

Brucite

Calcite

'Catlinite'

Celestine

Cerussite

Chalcocite

Chalcopyrite

Chromite

Chrysotile

'Clays'

'Clinopyroxene Subgroup'

Copper

Diamond

Dolomite

var: Ferroan Dolomite

Enstatite

Epidote

'Fayalite-Forsterite Series'

Felsőbányaite

Ferro-actinolite

Fluorapatite

Fluorite

Galena

Gibbsite

'Glass'

Glauconite

Goethite

Gold

Gypsum

var: Alabaster

var: Satin Spar Gypsum

var: Selenite

Hematite

Hemimorphite

Ilmenite

Iowaite (TL)

Iron

var: Kamacite

Isocubanite

Jarosite

Kaolinite

'K Feldspar'

'var: Adularia'

'Limonite'

'var: Stilpnosiderite'

Mackinawite

Magnesite

Magnetite

Malachite

'Manganese Oxides'

'var: Manganese Dendrites'

Marcasite

Melanterite

Merrillite

Millerite

Molybdenite

'Olivine'

Orthoclase

'Orthopyroxene Subgroup'

'Petrified Wood'

'Petroleum'

Pigeonite

'Plessite'

Prehnite

Pyrite

Pyroaurite

Pyrolusite

'Pyroxene Group'

Quartz

var: Agate

var: Amethyst

var: Carnelian

var: Chalcedony

var: Citrine

var: Jasper

var: Lake Superior Agate

var: Moss Agate

var: Smoky Quartz

Quenstedtite

Rutile

Sauconite

Schreibersite

Siderite

Smithsonite

Sphalerite

Spinel

Stanfieldite (TL)

Taenite

Tetrataenite (TL)

Tridymite

Troilite

'Wad'

Whitlockite

Wollastonite

Wurtzite

Zircon


74 valid minerals. 3 (TL) - type locality of valid minerals.

Rock Types Recorded

Note: this is a very new system on mindat.org and data is currently VERY limited. Please bear with us while we work towards adding this information!

Rock list contains entries from the region specified including sub-localities

Select Rock List Type

Alphabetical List Tree Diagram

Localities in this Region

USA
USA

This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Paul Garvin (1998): Iowa's Minerals: Their Occurrence, Origins, Industries, and Lore. University of Iowa Press, 260 pp.
Wayne Anderson (1998) Iowa's Geological Past: three billion years of earth history: University of Iowa Press, 424 pp.
Sinotte, S. (1969) The Fabulous Keokuk Geodes: Wallace-Homestead Press, Des Moines.

External Links

Iowa Geological Survey http://www.igsb.uiowa.edu

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