Strongly deformed Paleoproterozoic granitic intrusions in biotite schist (Spaghetti Canyon, Lower Granite Gorge, Grand Canyon, Arizona, USA).
What are metamorphic rocks?
Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet.
Process of Metamorphism:
The process of metamorphism does not melt the rocks, but instead transforms them into denser, more compact rocks. New minerals are created either by rearrangement of mineral components or by reactions with fluids that enter the rocks. Pressure or temperature can even change previously metamorphosed rocks into new types. Metamorphic rocks are often squished, smeared out, and folded. Despite these uncomfortable conditions, metamorphic rocks do not get hot enough to melt, or they would become igneous rocks!
Common Metamorphic Rocks:
Common metamorphic rocks include phyllite, schist, gneiss, quartzite and marble.
Foliated Metamorphic Rocks:
Some kinds of metamorphic rocks -- granite gneiss and biotite schist are two examples -- are strongly banded or foliated. (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied.
Non-Foliated Metamorphic Rocks:
Non-foliated metamorphic rocks do not have a platy or sheet-like structure. There are several ways that non-foliated rocks can be produced. Some rocks, such as limestone are made of minerals that are not flat or elongate. No matter how much pressure you apply, the grains will not align! Another type of metamorphism, contact metamorphism, occurs when hot igneous rock intrudes into some pre-existing rock. The pre-existing rock is essentially baked by the heat, changing the mineral structure of the rock without addition of pressure.
Learn more: Geologic units containing metamorphic rock
Related
Is glacier ice a type of rock?
Glacier ice, like limestone (for example), is a type of rock. Glacier ice is actually a mono-mineralic rock (a rock made of only one mineral, like limestone which is composed of the mineral calcite). The mineral ice is the crystalline form of water (H 2O). Most glacier ice forms through the metamorphism of tens of thousands of individual snowflakes into crystals of glacier ice. Each snowflake is a...
What are igneous rocks?
Igneous rocks (from the Latin word for fire) form when hot, molten rock crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface. Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies. Intrusive Igneous Rocks: Intrusive, or plutonic, igneous rock forms...
What are sedimentary rocks?
Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth's surface. Sedimentary rocks often have distinctive layering or bedding. Many of the picturesque views of the desert southwest show mesas and arches made of layered sedimentary rock. Common Sedimentary Rocks: Common sedimentary rocks include siltstone...
What is the difference between a rock and a mineral?
A mineral is a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties. Common minerals include quartz, feldspar, mica, amphibole, olivine, and calcite. A rock is an aggregate of one or more minerals, or a body of undifferentiated mineral matter. Common rocks include granite, basalt...
How did Half Dome, the massive rock monument in Yosemite National Park, acquire its unique shape?
At the head of the valley in Yosemite National Park - as if on a pedestal - stands Half Dome. It is smoothly rounded on three sides and a sheer vertical face on the fourth. Half Dome, which stands nearly 8,800 feet (2,682 meters) above sea level, is composed of granodiorite, and is the remains of a magma chamber that cooled slowly and crystallized thousands of feet beneath the Earth's surface. The...
Are there geologic maps or publications for where I live?
Detailed geologic mapping has not been completed for the entire United States, but maps are available for most locations. Geologic maps at many scales and from many sources are listed in the National Geologic Map Database. Some geologic maps can be purchased in hard copy through the USGS Store. Download digital geologic maps for entire states from the USGS Mineral Resources Online Geospatial Data...
Where can I find information about the geology and natural history of National Parks?
Our National Parks are the showcases of our nation's geological heritage. The National Park Service has websites for most individual parks that include information about their geology and natural history. A source of information from the USGS is our Geology and Ecology of National Parks website. The website has listings for regions of the country; selected parks are listed within each region...
Strongly deformed Paleoproterozoic granitic intrusions in biotite schist
Strongly deformed Paleoproterozoic granitic intrusions in biotite schist (Spaghetti Canyon, Lower Granite Gorge, Grand Canyon, Arizona, USA).
Quartzite rock, flowering ground cover, East Mount Zion site, York County, Pennsylvania
Boulder of Hellam Conglomerate member of the Chickies Quartzite at East Mount Zion Superfund Site, York County, Pennsylvania. (Lisa Senior, USGS)
Boulder of Hellam Conglomerate member of the Chickies Quartzite at East Mount Zion Superfund Site, York County, Pennsylvania. (Lisa Senior, USGS)
Outcrop of Quartzite Within the Roanoke Rapids
An outcrop of quartzite within the Roanoke Rapids terrane near Coleman Lake. Laser ablation inductively coupled plasma mass spectrometry U-Pb geochronology on detrital zircon grains within this unit (conducted by the USGS LA-ICPMS Lab in Denver) will provide critical and precise geochronologic age control as a geologic framework model is developed and compiled
An outcrop of quartzite within the Roanoke Rapids terrane near Coleman Lake. Laser ablation inductively coupled plasma mass spectrometry U-Pb geochronology on detrital zircon grains within this unit (conducted by the USGS LA-ICPMS Lab in Denver) will provide critical and precise geochronologic age control as a geologic framework model is developed and compiled
Roanoke Rapids Graphite Schist, VA
Graphite schist from the Roanoke Rapids terrane in southeastern Virginia. Economic deposits of this critical mineral may exist in this relatively unexplored region, which has not been adequately mapped at scales larger than 1:250,000.
Graphite schist from the Roanoke Rapids terrane in southeastern Virginia. Economic deposits of this critical mineral may exist in this relatively unexplored region, which has not been adequately mapped at scales larger than 1:250,000.
Garnet Schist
Mineral: Garnet Schist
Primary Commodity: Garnet
Primary Commodity Uses: Garnet is mostly used for abrasives, water filtration, and some electronics
Mineral: Garnet Schist
Primary Commodity: Garnet
Primary Commodity Uses: Garnet is mostly used for abrasives, water filtration, and some electronics
Cordierite Hornfels
Hornfels rocks are metamorphic rocks. They usually start out as sedimentary rocks like sandstone or shale, but then volcanic material pushes up from below and bakes the sedimentary rock into a metamorphic one. Hornfels are known for being exceptionally tough and durable. This one is from Chantilly, VA.
Hornfels rocks are metamorphic rocks. They usually start out as sedimentary rocks like sandstone or shale, but then volcanic material pushes up from below and bakes the sedimentary rock into a metamorphic one. Hornfels are known for being exceptionally tough and durable. This one is from Chantilly, VA.
Cockeysville Marble
Marble is a famous metamorphic rock known for its use in sculpture and architecture. This particular marble came from the Campbell Quarry in Texas, Maryland.
Marble is a famous metamorphic rock known for its use in sculpture and architecture. This particular marble came from the Campbell Quarry in Texas, Maryland.
Metasedimentary Rocks at the Apple Creek Formation
USGS scientist Art Bookstrom looks at puzzling sedimentary structures in metasedimentary rocks of the Apple Creek Formation, near the Jackass prospect, near Iron Creek, in the southeastern part of the Idaho cobalt belt, in east-central Idaho.
USGS scientist Art Bookstrom looks at puzzling sedimentary structures in metasedimentary rocks of the Apple Creek Formation, near the Jackass prospect, near Iron Creek, in the southeastern part of the Idaho cobalt belt, in east-central Idaho.
Quartz veins across outcrops of granitic gneiss on Divide Mt., Alaska
Half-meter-thick quartz veins cut across outcrops of granitic gneiss on Divide Mountain along the Alaska-Yukon border, August 2015
Half-meter-thick quartz veins cut across outcrops of granitic gneiss on Divide Mountain along the Alaska-Yukon border, August 2015
Biotitic Meta-Sandstone in the Gunsight Formation
Outcrop of biotitic meta-sandstone in the lower part of the Gunsight Formation, cut by white quartz veins with alteration envelopes of coarsely crystalline black biotite and minor muscovite. USGS intern, Shane Kostka prepares to collect representative samples from this outcrop.
Outcrop of biotitic meta-sandstone in the lower part of the Gunsight Formation, cut by white quartz veins with alteration envelopes of coarsely crystalline black biotite and minor muscovite. USGS intern, Shane Kostka prepares to collect representative samples from this outcrop.
Related
Is glacier ice a type of rock?
Glacier ice, like limestone (for example), is a type of rock. Glacier ice is actually a mono-mineralic rock (a rock made of only one mineral, like limestone which is composed of the mineral calcite). The mineral ice is the crystalline form of water (H 2O). Most glacier ice forms through the metamorphism of tens of thousands of individual snowflakes into crystals of glacier ice. Each snowflake is a...
What are igneous rocks?
Igneous rocks (from the Latin word for fire) form when hot, molten rock crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface. Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies. Intrusive Igneous Rocks: Intrusive, or plutonic, igneous rock forms...
What are sedimentary rocks?
Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth's surface. Sedimentary rocks often have distinctive layering or bedding. Many of the picturesque views of the desert southwest show mesas and arches made of layered sedimentary rock. Common Sedimentary Rocks: Common sedimentary rocks include siltstone...
What is the difference between a rock and a mineral?
A mineral is a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties. Common minerals include quartz, feldspar, mica, amphibole, olivine, and calcite. A rock is an aggregate of one or more minerals, or a body of undifferentiated mineral matter. Common rocks include granite, basalt...
How did Half Dome, the massive rock monument in Yosemite National Park, acquire its unique shape?
At the head of the valley in Yosemite National Park - as if on a pedestal - stands Half Dome. It is smoothly rounded on three sides and a sheer vertical face on the fourth. Half Dome, which stands nearly 8,800 feet (2,682 meters) above sea level, is composed of granodiorite, and is the remains of a magma chamber that cooled slowly and crystallized thousands of feet beneath the Earth's surface. The...
Are there geologic maps or publications for where I live?
Detailed geologic mapping has not been completed for the entire United States, but maps are available for most locations. Geologic maps at many scales and from many sources are listed in the National Geologic Map Database. Some geologic maps can be purchased in hard copy through the USGS Store. Download digital geologic maps for entire states from the USGS Mineral Resources Online Geospatial Data...
Where can I find information about the geology and natural history of National Parks?
Our National Parks are the showcases of our nation's geological heritage. The National Park Service has websites for most individual parks that include information about their geology and natural history. A source of information from the USGS is our Geology and Ecology of National Parks website. The website has listings for regions of the country; selected parks are listed within each region...
Strongly deformed Paleoproterozoic granitic intrusions in biotite schist
Strongly deformed Paleoproterozoic granitic intrusions in biotite schist (Spaghetti Canyon, Lower Granite Gorge, Grand Canyon, Arizona, USA).
Strongly deformed Paleoproterozoic granitic intrusions in biotite schist (Spaghetti Canyon, Lower Granite Gorge, Grand Canyon, Arizona, USA).
Quartzite rock, flowering ground cover, East Mount Zion site, York County, Pennsylvania
Boulder of Hellam Conglomerate member of the Chickies Quartzite at East Mount Zion Superfund Site, York County, Pennsylvania. (Lisa Senior, USGS)
Boulder of Hellam Conglomerate member of the Chickies Quartzite at East Mount Zion Superfund Site, York County, Pennsylvania. (Lisa Senior, USGS)
Outcrop of Quartzite Within the Roanoke Rapids
An outcrop of quartzite within the Roanoke Rapids terrane near Coleman Lake. Laser ablation inductively coupled plasma mass spectrometry U-Pb geochronology on detrital zircon grains within this unit (conducted by the USGS LA-ICPMS Lab in Denver) will provide critical and precise geochronologic age control as a geologic framework model is developed and compiled
An outcrop of quartzite within the Roanoke Rapids terrane near Coleman Lake. Laser ablation inductively coupled plasma mass spectrometry U-Pb geochronology on detrital zircon grains within this unit (conducted by the USGS LA-ICPMS Lab in Denver) will provide critical and precise geochronologic age control as a geologic framework model is developed and compiled
Roanoke Rapids Graphite Schist, VA
Graphite schist from the Roanoke Rapids terrane in southeastern Virginia. Economic deposits of this critical mineral may exist in this relatively unexplored region, which has not been adequately mapped at scales larger than 1:250,000.
Graphite schist from the Roanoke Rapids terrane in southeastern Virginia. Economic deposits of this critical mineral may exist in this relatively unexplored region, which has not been adequately mapped at scales larger than 1:250,000.
Garnet Schist
Mineral: Garnet Schist
Primary Commodity: Garnet
Primary Commodity Uses: Garnet is mostly used for abrasives, water filtration, and some electronics
Mineral: Garnet Schist
Primary Commodity: Garnet
Primary Commodity Uses: Garnet is mostly used for abrasives, water filtration, and some electronics
Cordierite Hornfels
Hornfels rocks are metamorphic rocks. They usually start out as sedimentary rocks like sandstone or shale, but then volcanic material pushes up from below and bakes the sedimentary rock into a metamorphic one. Hornfels are known for being exceptionally tough and durable. This one is from Chantilly, VA.
Hornfels rocks are metamorphic rocks. They usually start out as sedimentary rocks like sandstone or shale, but then volcanic material pushes up from below and bakes the sedimentary rock into a metamorphic one. Hornfels are known for being exceptionally tough and durable. This one is from Chantilly, VA.
Cockeysville Marble
Marble is a famous metamorphic rock known for its use in sculpture and architecture. This particular marble came from the Campbell Quarry in Texas, Maryland.
Marble is a famous metamorphic rock known for its use in sculpture and architecture. This particular marble came from the Campbell Quarry in Texas, Maryland.
Metasedimentary Rocks at the Apple Creek Formation
USGS scientist Art Bookstrom looks at puzzling sedimentary structures in metasedimentary rocks of the Apple Creek Formation, near the Jackass prospect, near Iron Creek, in the southeastern part of the Idaho cobalt belt, in east-central Idaho.
USGS scientist Art Bookstrom looks at puzzling sedimentary structures in metasedimentary rocks of the Apple Creek Formation, near the Jackass prospect, near Iron Creek, in the southeastern part of the Idaho cobalt belt, in east-central Idaho.
Quartz veins across outcrops of granitic gneiss on Divide Mt., Alaska
Half-meter-thick quartz veins cut across outcrops of granitic gneiss on Divide Mountain along the Alaska-Yukon border, August 2015
Half-meter-thick quartz veins cut across outcrops of granitic gneiss on Divide Mountain along the Alaska-Yukon border, August 2015
Biotitic Meta-Sandstone in the Gunsight Formation
Outcrop of biotitic meta-sandstone in the lower part of the Gunsight Formation, cut by white quartz veins with alteration envelopes of coarsely crystalline black biotite and minor muscovite. USGS intern, Shane Kostka prepares to collect representative samples from this outcrop.
Outcrop of biotitic meta-sandstone in the lower part of the Gunsight Formation, cut by white quartz veins with alteration envelopes of coarsely crystalline black biotite and minor muscovite. USGS intern, Shane Kostka prepares to collect representative samples from this outcrop.
Updated Date: April 8, 2025