Color | Light | Intermediate (Includes Red or Brown) |
Dark (Includes Green) |
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Chief Minerals | Quartz Feldspar Calcite Dolomite Talc Muscovite Sericite |
About Equal Proportions of Light-colored and Dark-colored Minerals | Quartz Calcite Dolomite Feldspar Chlorite Hornblende Serpentine Biotite Pyroxene Actinolite Epidote Olivine Magnetite |
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Characterizing Accessory Minerals |
Muscovite, Sericite, Sillimanite, Kyanite, Cordierite, Tremolite, Wollastonite, Albite, Andalusite, Garnet, Phlogopite, Diopside, Enstatite, Staurolite, Glaucophane, Anthophyllite, Pyrophyllite, Chloritoid, Actinolite, Tourmaline, Epidote, Chiastolite, Olivine, Serpentine, Chlorite, Biotite, Graphite, Chondrodite, Scapolite | |||||||
Non-directional Structure Massive or Granulose |
Contact Metamorphism* |
Fine Grained (Aphanitic) |
Metaquartzite Marble Brucite Marble Soapstone: chiefly talc Hornfels: any metamorphic rock with nondirectional structure |
Metaquartzite Marble Skarn: pyroxene-garnet-carbonate hornfels Soapstone: chiefly talc Hornfels: any metamorphic rock with nondirectional structure Serpentine * |
Metaquartzite Marble Skarn: pyroxene-garnet-carbonate hornfels Graphite Marble Chlorite Marble Serpentine Marble (Ophicalcite) Hornfels: any metamorphic rock with nondirectional structure Serpentine * |
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Medium or Coarse Grained (Phaneritic) |
Metaquartzite Marble Brucite Marble Tremolite Marble Wollastonite Marble Tremolite Hornfels Wollastonite Hornfels Calc-silicate Hornfels: chiefly calc-silicate minerals |
Metaquartzite Marble Diopside Marble Chondrodite Marble Andalusite Hornfels Skarn: pyroxene-garnet-carbonate hornfels Garnet Hornfels Kyanite Hornfels Anthophyllite Hornfels Calc-silicate Hornfels Serpentine * Cordierite-Anthophyllite Hornfels |
Metaquartzite Marble Graphite Marble Chlorite Marble Olivine Marble Skarn: pyroxene-garnet-carbonate hornfels Actinolite Marble Actinolite-Epidote Hornfels Actinolite Hornfels Pyroxene Hornfels Epidote Hornfels Andalusite-Biotite Hornfels Serpentine * Eclogite: pyrope-omphacite hornfels Magnetite Rock Cordierite Hornfels Amphibolite: chiefly hornblende and/or plagioclase |
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Directional Structure Lineate or Foliate |
Mechanical Metamorphism | Cataclastic |
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Regional Metamorphism | Slaty | Most slates are dark colored | Silty Slate Green Slate Black Slate Spotted Slate Andalusite Spotted Slate Chiastolite Spotted Slate Biotite Spotted Slate Carbonaceous Slate Calcareous Slate |
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Phyllitic |
Phyllite is intermediate between slate and schist. It differs from slate in that crystallization of micaeous minerals imparts a sheen to the rock; it differs from schist in that grains are too small for megascopic identification. Phyllonite: a phyllite owing its fine grain to mylonitization |
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Schistose | Quartz-Mica Schist Talc Schist Sillimanite Schist Albite-Mica Schist Quartz-Sericite Schist Kyanite Schist Calcite Schist (Schistose marble) |
Mica Schist Chiastolite Schist Andalusite Schist Staurolite Schist Kyanite Schist Pyrophyllite Schist Garnet-Mica Schist Serpentine * Tourmaline-Mica Schist Anthophyllite Schist Staurolite-Kyanite Schist Sillimanite-Garnet Schist Graphite Schist Calcite Schist (Schistose marble) Schistose Quartzite |
Greenschist Chlorite Schist Chloritoid Schist Amphibolite (Hornblende Schist) Actinolite Schist Graphite Schist Pyroxene Schist Epidote-Chlorite Schist Hornblende-Biotite Schist Biotite-Chlorite Schist Serpentine * Tourmaline Schist Epidote Amphibolite Garnet-Pyroxene Amphibolite Garnet-Chlorite Schist |
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Gneissose |
Rhyolite Gneiss |
Granite Gneiss Syenite Gneiss Monzonite Gneiss Granodiorite Gneiss Anorthosite Gneiss Trachyte Gneiss Conglomerate Gneiss Arkose Gneiss Sandstone Gneiss Augen Gneiss: augen structure Biotite Gneiss Staurolite Gneiss Plagioclase Gneiss Garnet Gneiss Muscovite-Biotite-Quartz Gneiss Kyanite Gneiss Granulite: banding due to elongated quartz or feldspar grains |
Quartz Diorite Gneiss Diorite Gneiss Gabbro Gneiss Peridotite Gneiss Diabase Gneiss Pyroxene Gneiss Graywacke Gneiss Epidote Gneiss Garnet-Biotite Gneiss Skarn Gneiss Amphiolite Gneiss |
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Plutonic Metamorphism | Migmatitic | These rocks have a gneissose, streaked, or
irregular structure produced by intimate mixing of metamorphic and magmatic
materials. When they can be recognized as "mixed rock," they are called
migmatite or migmatite gneiss. They may originate by injection (injection
migmatite, injection gneiss, or lit-par-lit gneiss) or by differential fusion.
Many so-called migmatites probably originate by partial granitization or
by metamorphic differentiation. But at great depth these processes apparently
do not differ substantially from the igneous processes forming migmatite,
so the products are usually indistinguishable.
Migmatites are named by prefixing the rock name of the granitic material to the appropriate root as "granite migmatite," "monzonite injection migmatite," etc. |
* Serpentine is a product of hydrothermal alteration which some authorities
consider to be an igneous process and others a metamorphic process.
For this reason, serpentine appears both on this chart and on the igneous
rock chart.
As can be noted from the chart, naming a metamorphic rock consists chiefly of prefixing the structural term with mineral names or an appropriate rock name. The rock name indicates either the original rock, if recognizable, or the new mineral composition. The prefix "meta," as in "metagabbro," "metasandstone," "metatuff," etc., is applied to rocks that have undergone considerable recrystallization but have largely retained their original fabric. Most of the minerals listed as accessories are genetically important and if present should be included in the rock name regardless of their quantity.