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Michigan, USA
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Introduction

The State of Michigan is unique in that it is separated into two geographically distinct regions that are, for the most part, geologically different as well. The State is divided into an Upper and Lower Peninsula, separated by the Straits of Mackinaw between Mackinaw City and Saint Ignace. The state is divided by geology as well and features two very distinct areas. The first area includes all of the Lower Peninsula and approximately one-half (the eastern) portion of the Upper Peninsula, which consist mostly of Paleozoic aged sediments (mostly limestone and dolomite). The second area is the western half of the Upper Peninsula which is dominated by Archean and Proterozoic Precambrian aged gneiss, granites, basalts, and sandstones.

The boundary between the sediments to the east and mostly Precambrian rocks to the west extends from approximately Marquette in the north to Iron Mountain in the south. The following is a very brief description of the geology of Michigan. For a more detailed read, please see the many books published on the subject.

Precambrian Geology

The Precambrian rocks that dominate the western half of Michigan’s Upper Peninsula are very diverse and include both intrusive and extrusive varieties, as well as sediments and their metamorphic equivalents. Rocks of this period include those of the Canadian Shield, the Banded Iron Formations, and the Portage Lake Volcanics. Outcrops of these rocks can be found scattered throughout the area; however, in most cases, the rock record is either fragmentary and incomplete, or buried under overburden left by the glaciers.

Since their formation, much has happened to these rocks. The oldest, the Watersmeet Gneiss, has been dated to 3.56 billion years old, making it some of the oldest rock in North America. The Watersmeet Gneiss, as well as many other of the oldest rocks, have been subjected to at least three major crustal deformations and mountain building events. In addition, there have been at least four smaller scale deformation events in the area. These events were accompanied by the intrusion of granitic rocks deep within the crust that were later brought to the surface by uplift and erosion. In addition to the granitic intrusions, at least four periods of volcanism have been discovered that produced basalt rocks and pyroclastic deposits, as well as dikes and dike swarms composed of diabase and gabbro.

Since their formation, metamorphism of these rocks has produced a multitude of new and reworked rocks and minerals. The greenstone, gneiss, quartzite, marble, slate, and schist found throughout the western Upper Peninsula can all trace their roots to much older rocks. The youngest rocks in this group are the Portage Lake Volcanics, which include basalts, conglomerates, and sandstones. These packages of rocks have remained largely unchanged since their formation, except for very shallow burial metamorphism of the basalts to the prehnite/pumpellyite grade. Rocks of the Portage Lake Volcanic series are associated with the Midcontinent Rift, a great tear in the Earth’s crust that nearly separated North America in two. The Rift can be traced from near Detroit northwest through the Lower Peninsula into Lake Superior, then arching back southwestward across the Keweenaw Peninsula and into Wisconsin.

Many of the metallic mineral deposits in Michigan come from the Precambrian rocks of the western Upper Peninsula, including the world renowned native copper deposits on the Keweenaw Peninsula and the banded iron formation deposits of the Marquette, Menominee, and Gogebic Ranges. Other minerals of note to come from the Precambrian rocks include silver, prehnite, garnet, goethite, datolite, gold, and the famous Lake Superior agate.


Bedrock geology map (MDNR)


Paleozoic Rocks

Rocks of the Paleozoic are represented by formations that underlie all of the Lower Peninsula and the eastern half of the Upper Peninsula. All of these rocks are sedimentary that were deposited in a shallow sea over a period of about 370 million years beginning in the Cambrian and lasting through the Pennsylvanian. During this time, approximately 14,000 feet of mostly limestones, dolomites, sandstones, and shales were deposited on top of the Precambrian basement rocks; the same rocks that are exposed in the western Upper Peninsula. As these sediments were being deposited, the entire region began to downwarp into a bowl-shaped depression. This depression, called the Michigan Basin, dominates the geology of the Lower Peninsula. The basin dips inward from the edges at approximately 2 degrees until reaching the center of the basin near the geographic center of the Lower Peninsula. Most of the Paleozoic rocks in the basin are derived from marine sediments; however, a few fluvial sandstones and coal deposits are exceptions.

What is unique about the entire sedimentary package is that they have not been metamorphosed or subjected to igneous intrusion or volcanism. Structurally, the rocks have not been subjected to major deformation except for minor folding and faulting near the edges of the basin. In essence, these rocks have remained sedimentary rock, modified only slightly by weathering and the action of groundwater. The rocks of the Paleozoic do not represent a complete record of sedimentation in the Michigan Basin. Several times during the sedimentation, uplift interrupted the sinking of the basin which is characterized by erosion, or at least non-deposition, and has created several time gaps, or unconformities. While very few metallic minerals are found in the Paleozoic rocks, almost all of Michigan’s oil and natural gas reserves are found in the Michigan Basin rocks. Also found in the basin are large economic deposits of limestone and dolomite, including the world’s largest limestone quarry located near Rogers City, and large salt deposits under Detroit, Michigan.

Post Pennsylvanian and Pleistocene Geology

This period is marked by the fact that very few rocks are found with an age between the end of the Pennsylvanian and the Pleistocene glacial deposits. This “Lost Interval” in geologic time is represented only by a small area of red beds located near the center of the Basin which are completely buried by glacial deposits and are only known from drill core data. The age of these red beds has been interpreted as youngest Jurassic based on fossil plant spores extracted from the drill cores. Beyond these rocks, no rock record is preserved from this period; this is likely due to a change from deposition to a period of slow erosion on the landscape until the Pleistocene Epoch and the arrival of the glaciers from Canada. It is known that at least four major glaciations took place during the Pleistocene, but only the youngest of these (the Wisconsinan) are preserved in Michigan. The surficial deposits from this epoch include clastic sediments, drift, gravels, sands, and clays. Surface features found scattered across both peninsulas that can be directly attributed to glacial activity include kettle lakes, eskers, lateral and end moraines, and kame deposits. The sediments carried in by the glaciers, while not loaded with economic minerals that can be mined, are very rich in nutrients that make them excellent for growing crops that supply food to millions of people around the world.

One additional rock type that deserves mention are the kimberlite deposits found in Upper Michigan. These kimberlites are thought to have been emplaced during the Cretaceous Period between 150 and 100 million years ago, during the time dinosaurs roamed the earth! First discovered in 1971, these deposits have generated much interest both popular and scientific. To date, no economic diamond deposit has been discovered in Michigan. It has been suggested that Michigan did not have the correct tectonic setting favourable for a highly diamondtiferous kimberlite. It is also believed that the Mid Continent Rift had a very destructive influence on the lithospheric mantle, thus destroying any diamonds being stored in the mantle prior to the kimberlite eruptions. Currently there is no active diamond exploration taking place in Michigan; however, there are a number of untested targets and placer deposits of indicator minerals occurrences in the state. Maybe one day, the state of Michigan will produce the next “diamond rush”?

The State of Michigan is unique geologically, and to truly understand its complexity the rocks must be seen in person and not simply read about in a textbook or trade magazine. Not many places on Earth can boast areas where a person can stand on 3.6 billion year old Archean gneiss then take one step and stand on glacial deposits just 7,000 years old; that is quite an amazing thought!
[Paul Brandes 2011]

Mineral List

Mineral list contains entries from the region specified including sub-localities
Acanthite
Actinolite
Aegirine
Aeschynite-(Y)
Albite
var: Andesine
var: Oligoclase
var: Peristerite
'Albite-Anorthite Series'
Algodonite
'Allanite'
Allanite-(Ce)
Almandine
Aluminoceladonite
Alunite
Amphibole Supergroup
var: Uralite
Analcime
Anatase
Andalusite
Andradite
Anglesite
Anhydrite
Anilite
Ankerite
Annabergite
Anorthite
var: Bytownite
var: Labradorite
Anthonyite (TL)
Anthophyllite
Antigorite
var: Picrolite
Antimony
'Apatite'
'var: Carbonate-rich Apatite'
'var: Collophane'
'var: Phosphorite'
'Aphrosiderite'
'Apophyllite'
Aragonite
var: Flos Ferri
Argentopentlandite
Arsenopyrite
'Asbestos'
Atacamite
Augite
'Axinite Group'
Axinite-(Mg)
Azurite
Babingtonite
Baryte
Bassetite
'Bastnäsite'
Bastnäsite-(Ce)
Bastnäsite-(Y)
Bertrandite
Beryl
'Betafite Group'
'Biotite'
Bismuth
Bismuthinite
'Bitumen'
Bornite
Brannerite
Braunite
Britholite-(Y)
Brochantite
Brookite
Brucite
Buttgenbachite
Calcite
var: Anthraconite
var: Manganoan Calcite
Calcurmolite
Calumetite (TL)
Carbonatecyanotrichite
Carnallite
Cassiterite
Celadonite
Celestine
Centennialite (TL)
Cerussite
'Chabazite'
Chalcanthite
Chalcocite
Chalconatronite
Chalcopyrite
Chamosite
var: Thuringite
Cheralite
'Chert'
'var: Taconite'
Chervetite
Chlorapatite
Chlorartinite
'Chlorite Group'
'var: Brunsvigite'
Chloritoid
var: Masonite
Chromite
Chrysocolla
Chrysotile
Cinnabar
Clausthalite
Clinochlore
var: Delessite
var: Diabantite
var: Pennine
var: Ripidolite
Clinochrysotile
'Clinopyroxene Subgroup'
Clinozoisite
'Coal
var: Bituminous Coal'

Cobaltite
'Columbite'
Columbite-(Fe)
Conichalcite
Connellite
Copiapite
Copper
'Copper Stain'
Cordierite
Coronadite
Corrensite
Corundum
Cosalite
Covellite
Crednerite
Cryptomelane
Cubanite
Cummingtonite
Cuprite
var: Chalcotrichite
Datolite
Daubréelite
Diamond
Diaphorite
Dickite
Digenite
Diopside
var: Schefferite
Dioptase
Djurleite
Dolomite
var: Ferroan Dolomite
Domeykite
Dyscrasite
Edenite
Enargite
Enstatite
var: Bronzite
Epidote
Epsomite
Erythrite
Euclase
Eugenite
Euxenite-(Y)
Fassinaite
'Faujasite Subgroup'
Fayalite
'Feldspar Group'
Ferberite
Ferrimolybdite
Ferro-hornblende
'Flint'
Fluorapatite
Fluorapophyllite-(K)
Fluorite
var: Chlorophane
var: Yttrofluorite
Forsterite
Gahnite
Galena
'Garnet'
Geikielite
Gerhardtite
Gersdorffite
Gibbsite
Glauconite
Goethite
Gold
var: Electrum
Graphite
Grayite
Greenalite
Greenockite
Greigite
Groutite
Grunerite
Guérinite
'Gummite'
Gypsum
var: Alabaster
var: Satin Spar Gypsum
var: Selenite
'Halfbreed'
Halite
'Halloysite'
Halotrichite
Hausmannite
Hedenbergite
Hematite
var: Martite
var: Specularite
Hessite
Hetaerolite
'Heulandite'
Heulandite-Ca
Hexahydrite
Hisingerite
Hollandite
'Hornblende'
Humboldtine
Hydrocerussite
'Hydrohausmannite'
Hydromagnesite
Hydroxylapatite
var: Carbonate-rich Hydroxylapatite

Hydrozincite
'Hypersthene'
'Iddingsite'
Ilmenite
Iron
var: Kamacite

Jacobsite
Jarosite
'Jaspillite'
Kamiokite
Kaolinite
Kasolite
'Kelyphite'
'K Feldspar'
'var: Adularia'
Kinoite
Kochkarite
Koutekite
Kutnohorite
Kyanite
Langite
Laumontite
Lavendulan
'Lechatelierite'
Lepidocrocite
'Leucoxene'
Likasite
'Limonite'
Lizardite
Luanheite
Macfallite (TL)
Mackinawite
Magnesio-riebeckite
Magnetite
Malachite
'Manganese Oxides
var: Manganese Dendrites'

Manganite
Manganocummingtonite
Marcasite
Margarite
Maucherite
Meionite
Melanterite
'Melilite'
Meneghinite
Mercury
Merrillite
Mesolite
Meta-autunite
Metacinnabar
Metatorbernite
Metatyuyamunite
'Mica Group'
Microcline
var: Ferruginous Microcline
Microlite Group
Millerite
Mimetite
Minnesotaite
Mirabilite
'Mohawkite'
Molybdenite
'Monazite'
Monazite-(Ce)
Monohydrocalcite
Monticellite
Montmorillonite
Montroseite
Moolooite
Mottramite
Muscovite
var: Fuchsite
var: Illite
var: Sericite
Nacrite
Nantokite
Natrojarosite
Natrolite
Neltnerite
Neotocite
Nickeline
Nickelskutterudite
var: Chloanthite
Nontronite
Olivenite
'Olivine'
Orientite
Orthochamosite
Orthoclase
'Orthopyroxene Subgroup'
Otavite
Palygorskite
Paragonite
Paramelaconite
Pararammelsbergite
Paratacamite
Pargasite
Paxite
Pecoraite
Pentlandite
Perovskite
'Perthite'
'Petoskey Stone'
Pharmacolite
Phlogopite
Pickeringite
Picropharmacolite
Pigeonite
Plancheite
'Plessite'
Polyhalite
Posnjakite
Powellite
Prehnite
'Prochlorite'
Pseudomalachite
'Psilomelane'
'Pumpellyite'
Pumpellyite-(Fe2+)
Pumpellyite-(Mg) (TL)
var: Chlorastrolite
Pumpellyite-(Mn2+)
Pyrite
var: Bravoite
'Pyrochlore'
Pyrolusite
Pyrope
Pyrophyllite
Pyrostilpnite
Pyroxmangite
Pyrrhotite
Quartz
var: Agate
var: Amethyst
Quartz
var: Carnelian

var: Chalcedony
var: Jasper
var: Lake Superior Agate
var: Milky Quartz
var: Rock Crystal
var: Smoky Quartz
Ramdohrite
Rammelsbergite
Rauenthalite
Rhodochrosite
Rhodonite
Riebeckite
Romanèchite
Rutherfordine
Rutile
Safflorite
Sainfeldite
Sanidine
Saponite
'Scapolite'
Scheelite
Schorl
Schreibersite
Seamanite (TL)
Sepiolite
'Serpentine Group'
Shigaite
Shuiskite
'Shungite'
Siderite
Siegenite
Silicon
Sillimanite
Silver
var: Amalgam
Sklodowskite
Skutterudite
var: Smaltite
'Smectite Group'
Smithsonite
Spertiniite
Spessartine
Sphalerite
Spinel
Spodumene
Starkeyite
Staurolite
'Stilbite'
Stilbite-Ca
Stilpnomelane
Stromeyerite
Strontianite
Sudoite
Sulphur
Sussexite
Sylvite
Synchysite-(Ce)
Synchysite-(Y)
Szaibélyite
Taenite
Talc
var: Beaconite
var: Steatite
Tangeite
Tantalite-(Fe)
Tanteuxenite-(Y)
Tapiolite-(Fe)
Tellurium
Tellurobismuthite
Tenorite
Tetrahedrite
var: Argentian Tetrahedrite
Thermonatrite
'Thomsonite'
Thomsonite-Ca
Thorite
Titanite
Topaz
'Tourmaline'
Tremolite
Troilite
Trona
Tsumoite
Tyrolite
Tyuyamunite
Uraninite
var: Pitchblende
var: Thorian Uraninite
Uranophane
Uranospinite
Uvarovite
Vaterite
Vermiculite
Veszelyite
Violarite
Vivianite
Vladimirite
Volborthite
Volynskite
Vonsenite
Wairakite
Wakefieldite-(Y)
Whewellite
Widenmannite
Wilcoxite
Witherite
Wollastonite
Wroewolfeite
Wulfenite
Wurtzite
Xenotime-(Y)
Xilingolite
Xonotlite
Zircon
var: Hyacinth
Zoisite


497 entries listed. 351 valid minerals. 6 type localities (valid minerals).

Localities in this Region

USA
USA

The above list 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

Carlson, S.M., and Floodstrand, W., 1994. Michigan Kimberlites and Diamond Exploration Techniques (abstract), in Institute on Lake Superior Geology Proceedings, 40th Annual Meeting, Houghton, Michigan, v.40, part 4.

Dorr, J.A., and Eschman, D.F., 1970. Geology of Michigan: University of Michigan Press, 476 p.

Dyl, S.J., and Wilson, M.L., 1992. Michigan Copper Country: Mineralogical Record, v.23, no.2, p. 24-28.

Heinrich, E.W., 1976. The Mineralogy of Michigan: Michigan Department of Natural Resources, Geological Survey Division, Bulletin 6, 225 p.

LaBerge, G.L., 1994. Geology of the Lake Superior Region: Geoscience Press, 313 p.

Robinson, G.W., 2004. Mineralogy of Michigan: Michigan Technological University, 252 p.

External Links


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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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