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Home , Arkose, Augite, Enstatite, Epidote, Felsite, Forsterite

Metamorphic Rocks All of the rocks listed below occur in Michigan.

Texture Name Diagnostic Features Fine grained; most or all grains invisible to the naked eye; similar position in adjacent folia (bands); smooth, even slaty . Fine grained; mineral grains barely or not visible; similar composition in adjacent folia; folia minutely wavy. FOLIATED Medium grained; many of mineral grains visible to the naked eye; relatively uniform and similar mineral composition in adjacent folia; folia irregular and discontinuous; often rich in . Coarse to medium grained; mineral grains visible to naked eye; adjacent folia of different mineral composition; contains abundant ; folia irregular and discontinuous.

NONFOLIATED Chiefly composed of ; if original sedimentary quartz grains are (may be faintly banded due distinguishable, note that rock breaks through the grains rather than along to presence of original grain boundaries. May be banded. stratification) Chiefly (CaCO ) or (CaMg(CO ) ). 3 3 2

Varieties of and are subdivided on the basis of their mineral composition, which is determined largely by the composition of the original rock, the “grade” or intensity of , and the kinds of chemical substances either removed or introduced during metamorphism. Two examples from Michigan are staroulite schist and cummintonite schist. Both of these are from the western northern peninsula.

Metamorphic Rock Sources

Source Result alteration occurs at low in-and intensity. Little or no change î î î Marble Dolomite î thereafter Quartz alteration occurs at moderate to high intensities. No mineral change î î î Quartzite because original composition is simple - SiO2

Shale î î î Slate, Phyllite, Schist, Gneiss,

Peat î î î Lignite, Bituminous, Anthracite, In general, the and rich rocks are altered to schists Igneous Schists and , whereas the silica and aluminum rich rocks form rocks î î î and gneisses, but almost any variation is possible because of variations (many î Gneisses in intensity of metamorphism and also because of the opportunity types) for the addition or removal of elements.

For more information see the of Michigan, 1991; Dorr & Eschman, University of Michigan Press, Ann Arbor, Michigan.

Rock Types and Rocks found in Michigan - www.deq.state.mi/gsd - 1 of 5

Metamorphic Relationships between Chemical Composition, Grade of Metamorphism, and Formed

Cations Grade of Metamorphism Present Low Medium High

Si Quartz

Kyanite Si, Al

Si, Al, Fe

Serpentine Si, Mg

Anthopyllite / Cummingtonite Si, Mg, Fe /

Chlorite Si, Mg, Fe, Al Almandite

Si, Ca

Tremolite / Si, Ca, Mg, Fe /

Hornblende Si, Ca, Mg, Fe, Al

Epidote Group Si, Ca, Al Ca / Prehnite

Albite Si, Ca, Na, Al

Muscovite Si, K, Al

Si, K, Al, Fe, Mg

For more information see the Geology of Michigan, 1991; Dorr & Eschman, University of Michigan Press, Ann Arbor, Michigan.

Rock Types and Rocks found in Michigan - www.deq.state.mi/gsd - 2 of 5

Igneous Rocks Predominant Minerals, Reflecting Chemical Composition

Ferromagnesian Minerals (Biotite, Ú Ferromagnesian Minerals Feldspar , Augite) Minerals Only Feldspar and Quartz Predominant Predominately (No Quartz, (No Quartz) Plagioclase Textures Ü No Feldspar) Feldspar (No Quartz) VOLCANIC or Pyroclastic or - fragmental often fragments over 4 classed as millimeters in diameter Extrusive igneous VOLCANIC or ASH rocks fragments less than ~ millimeters in diameter Glassy —if dense or Extrusive igneous massive SCORIA rocks —if frothy Aphanitic Fine-grained Felsite , too small

to see Extrusive igneous and rocks Phaneritic Granite (with and a Granular Mineral ( mineral such as orthoclase and crystals clearly microcline predominate) visible. May be (pyroxene alone) Intrusive igneous Serpentine (plagioclase feldspars rocks (altered olivine and predominate) pyroxene minerals)

Highlighted Rocks are found in Michigan . Amygdaloidal Structure is that produced in a vesicular rock by filling of vesicles with mineral matter. If a rock has amygdules, use a compound name, for example, amygdaloidal basalt . In Michigan the State Gem variety chlorastrolite and many other interesting minerals are found having filled in these voids.

SCORIA is a vesicular of fine or glassy texture, usually of basaltic composition. Some gas grill manufacturers use scoria above the burners.

If a rock falls in one of the above categories on the chart but is porphyritic (visible crystals in a fine grained groundmass or ) it is given a compound name, for example, granite (or porphyritic granite), and basalt porphyry (or porphyritic basalt).

For more information see the Geology of Michigan, 1991; Dorr & Eschman, University of Michigan Press, Ann Arbor, Michigan.

Rock Types and Rocks found in Michigan - www.deq.state.mi/gsd - 3 of 5

Sedimentary Rocks I Detrital or Clastic (Exogenic) Main Mineral Constituents and Texture

Calcareous Ú Minerals fragments + Texture or Quartz + Quartz + Calcite Grains calcite Grain Size Ü Quartz Feldspar Matrix (not inter grown crystals) (± calcite (± cement) (± cement) (± cement) and calcite cement grains) Gravel Quartzose Arkosic Graywacke Limestone Coquina Bioclastic Conglomerate Conglomerate Conglomerate Conglomerate (if fossil Conglomerate Coarse grained if fragments are if fragments are if fragments are if fragments are fragments (if fossil Majority of rounded rounded rounded rounded dominant or fragments grains over 2 Quartzose Arkosic Graywacke Limestone abundant) common to mm. in di ameter Breccia if Breccia if Breccia if few) fragments are fragments are fragments are Breccia if angular angular angular fragments are angular Quartzose Graywacke Calcarenite Coquina Bioclastic (or Arkosic (or graywacke (or detrital Calcarenite Medium grained Sandstone sandstone) sandstone) limestone) Majority of grains 2 mm. to 1/16 mm. in diameter - Visible to naked eye Silt Fine grained Majority of grains from 1/16 Limestone mm. to 1/256 mm. Invisible to (difficult to distinguish naked eye (Very (the is difficult to difficult to distinguish without magnification from endogenous distinguish or laboratory work) types of limestone) different eye but feels gritty when scratched with fingernail Clay Very fine grained Majority of grains less than 1/256 mm. Feels Lithographic Limestone smooth when scratched with fingernail Earthy odor when damp

Highlighted Rocks are found in Michigan .

Angular grains or particles are referred to as immature, whereas more rounded grains or particles are referred to as mature.

For more information see the Geology of Michigan, 1991; Dorr & Eschman, University of Michigan Press, Ann Arbor, Michigan.

Rock Types and Rocks found in Michigan - www.deq.state.mi/gsd - 4 of 5

Sedimentary Rocks II Chemical or Biochemical (Endogenic) Main Mineral Constituents and

Hematite Halite Carbonaceous Minerals Ú Quartz Calcite (Possibly (Possibly (Plant Ü (or opal) (or Dolomite) Some Silica Some Fossils Remains) and/or Calcite) Anhydrite) Fossiliferous Limestone or Fossiliferous Peat /. Fossils DIATOMITE (if diatoms) Dolomite Lignite predominant RADIOLARITE May be named for or major Bitumino (if radiolarians) the predominant us fossil type. like Coralline limestone Crinoidal dolomite

DIATOMACEOU Fossiliferous Fossils some S or Limestone or subordinate Iron rare rare RADIOLARIAN or minor Fossiliferous Dolomite

Fossils rare or OOLITIC absent Chert , IRON Rock Rock Minerals in a Limestone (fossils rare) ANTHRACITE Salt Gypsum chemically Flint Dolomite (Halite) precipitated COAL Cherty (TRAVERTINE ) crystalline intergrowth (fossils absent) Evaporites

Highlighted Rocks are found in Michigan .

For more information see the Geology of Michigan, 1991; Dorr & Eschman, University of Michigan Press, Ann Arbor, Michigan.

Rock Types and Rocks found in Michigan - www.deq.state.mi/gsd - 5 of 5