Geology: Most Popular Articles
These articles are the most popular over the last month.
Rock Picture Gallery | Photos of Rocks
Pictures and descriptions of rocks on About.com Geology
Pictures and descriptions of rocks on About.com Geology
Rock Identification Tables
Three tables cover 37 of the most common rock types, with simple ways to distinguish them.
Three tables cover 37 of the most common rock types, with simple ways to distinguish them.
About Igneous Rocks
The three great rock classes--igneous, sedimentary and metamorphic--are introduced with igneous rocks.
The three great rock classes--igneous, sedimentary and metamorphic--are introduced with igneous rocks.
Mineral Picture Gallery
The mineral wing of the About Geology Picture Gallery.
The mineral wing of the About Geology Picture Gallery.
Landform Picture Gallery
The landform wing of the About Geology Picture Gallery.
The landform wing of the About Geology Picture Gallery.
About Sedimentary Rocks
The second of the three great rock classes is introduced with photos.
The second of the three great rock classes is introduced with photos.
Basalt
Basalt from Hawaii with vesicles and olivine grains.
Basalt from Hawaii with vesicles and olivine grains.
Granite - Picture of Granite
Picture of a salt-and-pepper granite specimen from central California.
Picture of a salt-and-pepper granite specimen from central California.
Sandstone
A large boulder of sandstone, with visible layering features, sits in a Berkeley landscaping yard.
A large boulder of sandstone, with visible layering features, sits in a Berkeley landscaping yard.
Limestone
Limestone appears in a New York roadcut.
Limestone appears in a New York roadcut.
About the Earth's Core
How we study the Earth's core and what it's made of.
How we study the Earth's core and what it's made of.
Gabbro
Gabbro is the plutonic equivalent of basalt.
Gabbro is the plutonic equivalent of basalt.
Schist
Schist is a metamorphic rock that comes in many varieties.
Schist is a metamorphic rock that comes in many varieties.
Shale
Shale or mudstone forms on the sea floor.
Shale or mudstone forms on the sea floor.
Diorite
Diorite is a plutonic rock, like granite without quartz.
Diorite is a plutonic rock, like granite without quartz.
Andesite
Andesite from the Sutter Buttes, California.
Andesite from the Sutter Buttes, California.
Obsidian
Obsidian chunk from the Napa Valley volcanoes.
Obsidian chunk from the Napa Valley volcanoes.
About Metamorphic Rocks
The three great rock classes--igneous, sedimentary and metamorphic--are introduced with photos, finishing with metamorphic.
The three great rock classes--igneous, sedimentary and metamorphic--are introduced with photos, finishing with metamorphic.
Mohs Scale of Relative Mineral Hardness
The ten-mineral Mohs scale of relative hardness, based on what scratches what.
The ten-mineral Mohs scale of relative hardness, based on what scratches what.
Gneiss
A fresh boulder of meat-colored Pinto Gneiss, in Joshua Tree National Park, shows the characteristics of this metamorphic rock type.
A fresh boulder of meat-colored Pinto Gneiss, in Joshua Tree National Park, shows the characteristics of this metamorphic rock type.
Slate - Picture of Slate
Slate displays a range of earthy colors.
Slate displays a range of earthy colors.
Chert
Chert pebbles from California.
Chert pebbles from California.
About Quartz
quartz grains sio 2 conchoidal fracture quartz sand: Quartz alone and in rocks, with some notes.
quartz grains sio 2 conchoidal fracture quartz sand: Quartz alone and in rocks, with some notes.
Aa Lava
A glowing flow of aa lava advances from the Puu Oo eruption on Hawaii island.
A glowing flow of aa lava advances from the Puu Oo eruption on Hawaii island.
Felsite
Felsite is the extrusive equivalent of granite.
Felsite is the extrusive equivalent of granite.
Quartzite
A boulder of tough, solid quartzite sits by a Las Vegas building.
A boulder of tough, solid quartzite sits by a Las Vegas building.
Siltstone
Siltstone, like sandstone but much finer grained.
Siltstone, like sandstone but much finer grained.
About the San Andreas Fault
Home page for everything about the San Andreas fault.
Home page for everything about the San Andreas fault.
Breccia
Breccia takes many forms; this photo shows a pebble of a fault breccia.
Breccia takes many forms; this photo shows a pebble of a fault breccia.
Scoria
Scoria from a Californian volcano.
Scoria from a Californian volcano.
Conglomerate
Conglomerate is a sign of a vigorous environment.
Conglomerate is a sign of a vigorous environment.
Fossil Picture Gallery
Pictures of fossils in the About Geology Picture Gallery.
Pictures of fossils in the About Geology Picture Gallery.
Rock Gypsum
Rock gypsum from a Nevada roadside.
Rock gypsum from a Nevada roadside.
Pumice
Pumice from a Californian volcano.
Pumice from a Californian volcano.
Marble
Marble is metamorphosed limestone.
Marble is metamorphosed limestone.
Graphite - Graphite Specimen
Graphite in its raw form.
Graphite in its raw form.
Arkose
Arkose from the Fountain Formation of Colorado.
Arkose from the Fountain Formation of Colorado.
Glacier Picture Gallery
Pictures of glacial features and the processes of glaciers.
Pictures of glacial features and the processes of glaciers.
About the Earth's Mantle
A look at six different aspects of the Earth's mantle.
A look at six different aspects of the Earth's mantle.
Porphyry
Porphyry is a widely varying type of igneous rock.
Porphyry is a widely varying type of igneous rock.
Coquina
Coquina is a sedimentary rock made of shell fragments.
Coquina is a sedimentary rock made of shell fragments.
Phyllite
Photo of phyllite showing its micaceous sheen.
Photo of phyllite showing its micaceous sheen.
Wacke or Graywacke
Wacke or graywacke is a sloppy kind of sandstone.
Wacke or graywacke is a sloppy kind of sandstone.
Amphibolite
Amphibolite is metamorphosed basaltic rock.
Amphibolite is metamorphosed basaltic rock.
Coal
Coal is fossil peat.
Coal is fossil peat.
Serpentinite
Serpentinite, the California state rock, at the Oakland Museum of California.
Serpentinite, the California state rock, at the Oakland Museum of California.
Gypsum
Clear specimens and desert roses composed of gypsum.
Clear specimens and desert roses composed of gypsum.
About Feldspar
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Rhyolite
Rhyolite from the Sutter Buttes, California.
Rhyolite from the Sutter Buttes, California.
Plate Tectonics - The World's Crustal Plates
The Earth's crustal plates, from the U.S. Geological Survey
The Earth's crustal plates, from the U.S. Geological Survey
Tuff
Tuff forms a cliff of tierra blanca in El Salvador.
Tuff forms a cliff of tierra blanca in El Salvador.
Pegmatite
Pegmatite in a Colorado boulder.
Pegmatite in a Colorado boulder.
Dolomite Rock
A chunk of coarsely crystalline dolomite.
A chunk of coarsely crystalline dolomite.
Syenite
Hand specimen of syenite.
Hand specimen of syenite.
Muscovite
Muscovite or white mica, a nice hand specimen from New York state.
Muscovite or white mica, a nice hand specimen from New York state.
Agate
Agate is the name for the best quality of chert.
Agate is the name for the best quality of chert.
Plagioclase Feldspar
Plagioclase feldspar is a major rock-forming mineral.
Plagioclase feldspar is a major rock-forming mineral.
Pahoehoe Lava
A flow of fresh hot pahoehoe lava smothers an old Hawaiian footpath.
A flow of fresh hot pahoehoe lava smothers an old Hawaiian footpath.
Pyroxenite
Pyroxenite from the Feather River Ultramafics of the northern Sierra Nevada.
Pyroxenite from the Feather River Ultramafics of the northern Sierra Nevada.
Biotite
Biotite is black mica, a common rock-forming mineral.
Biotite is black mica, a common rock-forming mineral.
Geyser
Photo of Castle Geyser, in Yellowstone National Park, Wyoming.
Photo of Castle Geyser, in Yellowstone National Park, Wyoming.
What Is a Rock?
Everyone knows what a rock is, until you ask what it is exactly.
Everyone knows what a rock is, until you ask what it is exactly.
Gems to Minerals, Minerals to Gems
microcline feldspar gemstone mineral rubellite tourmaline demantoid garnet taaffeite: Mineral names and their corresponding gem names.
microcline feldspar gemstone mineral rubellite tourmaline demantoid garnet taaffeite: Mineral names and their corresponding gem names.
What Is Geology?
The whole of Earth sciences, compressed to a nutshell.
The whole of Earth sciences, compressed to a nutshell.
Geologic Map of California
California geologic map, at four different scales.
California geologic map, at four different scales.
Granodiorite
A polished slab of granodiorite from southeastern New Hampshire.
A polished slab of granodiorite from southeastern New Hampshire.
Migmatite
Migmatite is highly metamorphosed rock.
Migmatite is highly metamorphosed rock.
About Granite
Granite is the signature rock of the continents.
Granite is the signature rock of the continents.
Potassium or Alkali Feldspar - Microcline (Amazonite)
Bright-green amazonite is an easy-to-recognize variety of microcline, a potassium or alkali feldspar.
Bright-green amazonite is an easy-to-recognize variety of microcline, a potassium or alkali feldspar.
Sedimentary Rock Gallery - Chert Nodule Interior
Interior of a chert nodule.
Interior of a chert nodule.
Eclogite
Eclogite, an extreme metamorphic rock from the mantle.
Eclogite, an extreme metamorphic rock from the mantle.
Lapilli Tuff
Lapilli tuff in a California outcrop.
Lapilli tuff in a California outcrop.
Olivine
Olivine grain in Kilauea basalt.
Olivine grain in Kilauea basalt.
Pictures of Geologic Features and Processes
Pictures of geologic features and the processes of geology.
Pictures of geologic features and the processes of geology.
Calcite
Photo of Iceland spar calcite rhomb showing double refraction, with notes.
Photo of Iceland spar calcite rhomb showing double refraction, with notes.
Mount St. Helens Eruption
Remembering a scientist who died in the 1980 eruption of Mount St. Helens.
Remembering a scientist who died in the 1980 eruption of Mount St. Helens.
Banded Iron Formation
Australian 'folded tiger iron' is a spectacular variety of banded iron formation.
Australian 'folded tiger iron' is a spectacular variety of banded iron formation.
Alabaster
An image of alabaster, or fine-grained travertine.
An image of alabaster, or fine-grained travertine.
Halite
Halite in three forms: rock salt, halite crystals and table salt.
Halite in three forms: rock salt, halite crystals and table salt.
Plate Tectonics in a Nutshell
A simple starting point for the basics of plate tectonics.
A simple starting point for the basics of plate tectonics.
Perlite
Perlite from a young rhyolite dome.
Perlite from a young rhyolite dome.
Geologic Map of Texas
Texas geologic map, courtesy of the state bureau of economic geology
Texas geologic map, courtesy of the state bureau of economic geology
Talc
Talc, the softest mineral.
Talc, the softest mineral.
The Tibetan Plateau
The largest highest place on Earth is a showcase of plate tectonics.
The largest highest place on Earth is a showcase of plate tectonics.
How to Identify Minerals
First steps in mineral identification.
First steps in mineral identification.
Natural Asphalt
Natural asphalt from the McKittrick oil seep.
Natural asphalt from the McKittrick oil seep.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
The three basic types of fault, with their nomenclature, in a nutshell.
Peat
Peat is the precursor of coal.
Peat is the precursor of coal.
1906 San Francisco Earthquake
The Great San Francisco Earthquake was the stuff of legend, but it really happened.
The Great San Francisco Earthquake was the stuff of legend, but it really happened.
Geotourism
Get down to earth around the world through geologic tourism.
Get down to earth around the world through geologic tourism.
Blueschist
Blueschist, close up and deployed in a decorative setting.
Blueschist, close up and deployed in a decorative setting.
Articles on Earthquakes
Features about earthquakes, seismology, and related phenomena from your About Geology Guide.
Features about earthquakes, seismology, and related phenomena from your About Geology Guide.
Greenstone
Greenstone in a California roadcut and outcrop.
Greenstone in a California roadcut and outcrop.
Magnetite
Magnetite--a genuine lodestone up close.
Magnetite--a genuine lodestone up close.
Travertine
Travertine, a low-density form of limestone.
Travertine, a low-density form of limestone.
Alluvial Fan
A wide alluvial fan debouches from a range in Montana.
A wide alluvial fan debouches from a range in Montana.
Earth Formation in a Nutshell
The straight story of how Earth began, as today's geologists tell it.
The straight story of how Earth began, as today's geologists tell it.
What Is a Mineral?
Minerals meet four criteria, more or less strict.
Minerals meet four criteria, more or less strict.
Articles on Volcanoes
Articles about volcanoes and related phenomena, from your About Geology Guide.
Articles about volcanoes and related phenomena, from your About Geology Guide.
Tombolo
A tombolo is a sandbar stretching from land to an island offshore.
A tombolo is a sandbar stretching from land to an island offshore.
Hornblende
A hornblende pocket in Sierra Nevada granite.
A hornblende pocket in Sierra Nevada granite.
Thunder Egg
Thunder eggs form in volcanic sediments. Inside is solid agate.
Thunder eggs form in volcanic sediments. Inside is solid agate.
The Lithosphere in a Nutshell
earthquake faults rock slab plate tectonics surface rocks lithosphere: What you need to know about the lithosphere
earthquake faults rock slab plate tectonics surface rocks lithosphere: What you need to know about the lithosphere
Sedimentary Rock Gallery - Arkose
Arkose in the gallery of sedimentary rocks.
Arkose in the gallery of sedimentary rocks.
Mountain Pictures - California Peaks
Great pictures of great Californian mountains.
Great pictures of great Californian mountains.
Sedimentary Rock Gallery - Coquina
Coquina is a conglomerate made of shell fragments.
Coquina is a conglomerate made of shell fragments.
Chalcedony
Chalcedony is the microcrystalline form of quartz.
Chalcedony is the microcrystalline form of quartz.
Diamond - Natural Diamond Specimen
A natural diamond grain from Congo shows rough crystal faces.
A natural diamond grain from Congo shows rough crystal faces.
Global Seismic Hazard Map Index
First page of the Global Seismic Hazard Map gallery.
First page of the Global Seismic Hazard Map gallery.
Geodes (Before)
Two small unbroken geodes offer the promise of glittering guts.
Two small unbroken geodes offer the promise of glittering guts.
Sedimentary Rock Gallery - Siltstone
Siltstone, in the gallery of sedimentary rocks.
Siltstone, in the gallery of sedimentary rocks.
Metamorphic Rock Gallery - Mica Schist
A dark mica schist from Manhattan.
A dark mica schist from Manhattan.
Fulgurite
A small Moroccan fulgurite records a lightning strike on sand.
A small Moroccan fulgurite records a lightning strike on sand.
Tectonic Plate Boundaries, Eastern Hemisphere
Plate boundaries of the Eastern Hemisphere: divergent, convergent, and transform.
Plate boundaries of the Eastern Hemisphere: divergent, convergent, and transform.
Surface Minerals
The thousands of minerals known in rocks become a mere handful at the Earth's surface.
The thousands of minerals known in rocks become a mere handful at the Earth's surface.
Greenschist
Greenschist, a dark-green silicate rock formed by metamorphism of old seafloor.
Greenschist, a dark-green silicate rock formed by metamorphism of old seafloor.
Actinolite
Actinolite, a green silicate mineral formed by the metamorphism of old seafloor.
Actinolite, a green silicate mineral formed by the metamorphism of old seafloor.
Cirque
A cirque in Labrador testifies to recent glaciation.
A cirque in Labrador testifies to recent glaciation.
Hanging Valley
A classic hanging valley frames Yosemite's Bridal Veil Falls.
A classic hanging valley frames Yosemite's Bridal Veil Falls.
Articles About Fossils
Articles about fossils from your About Geology Guide.
Articles about fossils from your About Geology Guide.
Geology Desktop Wallpaper Pictures
Free 800x600, 1024x768 and 1280x1024 geology pictures for your computer's desktop wallpaper.
Free 800x600, 1024x768 and 1280x1024 geology pictures for your computer's desktop wallpaper.
The Richter Scales
Nowadays, every earthquake magnitude scale is the Richter scale.
Nowadays, every earthquake magnitude scale is the Richter scale.
What Are Fossils?
Fossils are precious gifts from the geologic past.
Fossils are precious gifts from the geologic past.
The Precambrian in Brief
Four billion years condensed into two pages.
Four billion years condensed into two pages.
Fluorite
Fluorite, the standard for Mohs hardness 4, belongs in everyone's mineral collection.
Fluorite, the standard for Mohs hardness 4, belongs in everyone's mineral collection.
Geology and Society Picture Gallery
Where geology overlaps the wider culture.
Where geology overlaps the wider culture.
Lisbon Earthquake, 1 November 1755
Lisbon earthquake of 1 November 1755, images and notes.
Lisbon earthquake of 1 November 1755, images and notes.
The Biggest Eruptions
The biggest eruptions in history and prehistory
The biggest eruptions in history and prehistory
Corundum
Corundum, whether red ruby or sapphire of any other color, is hardness 9 on the Mohs scale.
Corundum, whether red ruby or sapphire of any other color, is hardness 9 on the Mohs scale.
Petroleum - Crude Oil
Crude oil washes up on the beach near Santa Barbara, California.
Crude oil washes up on the beach near Santa Barbara, California.
Pyrite
Pyrite grains and crystals in many settings.
Pyrite grains and crystals in many settings.
The Crust
The Earth's crust is exceptionally important, and not just because we live on it.
The Earth's crust is exceptionally important, and not just because we live on it.
Identify the Rock-Forming Minerals
Quick identification table for the minerals that form the majority of rocks.
Quick identification table for the minerals that form the majority of rocks.
Apatite
A blue-green specimen of this important phosphorus mineral.
A blue-green specimen of this important phosphorus mineral.
Half Dome, California, USA
Photo of Half Dome, Yosemite Valley, California, a classic exfoliation dome.
Photo of Half Dome, Yosemite Valley, California, a classic exfoliation dome.
Top 25 US Geology PhD Schools
These 25 American colleges grant the huge majority of the geology PhD's held by U.S. college faculty.
These 25 American colleges grant the huge majority of the geology PhD's held by U.S. college faculty.
About Tsunamis
Tsunamis or tidal waves--whatever you call them, watch out.
Tsunamis or tidal waves--whatever you call them, watch out.
Sedimentary Rock Gallery - Dolomite
Dolomite in the gallery of sedimentary rocks.
Dolomite in the gallery of sedimentary rocks.
Brachiopod
A typical brachiopod fossil.
A typical brachiopod fossil.
Dolomite
Closeup of granular dolomite.
Closeup of granular dolomite.
Kyanite - Picture of Kyanite
A specimen of the important indicator mineral kyanite.
A specimen of the important indicator mineral kyanite.
Geologic Time Scale: Precambrian Time
The Precambrian part of the geologic time scale.
The Precambrian part of the geologic time scale.
Arete
A jagged arete in Alaska glacier country.
A jagged arete in Alaska glacier country.
Cinder Cone
Puu ka Pele is a beautiful cinder cone on the flanks of Mauna Kea, Hawaii.
Puu ka Pele is a beautiful cinder cone on the flanks of Mauna Kea, Hawaii.
Valley Glacier - or Mountain or Alpine Glacier
Bucher Glacier, a typical valley - or mountain or alpine - glacier.
Bucher Glacier, a typical valley - or mountain or alpine - glacier.
Bre-X Gold Scandal
First there is a mountain of gold, then there is no mountain, then there is no gold mining company named Bre-X.
First there is a mountain of gold, then there is no mountain, then there is no gold mining company named Bre-X.
Stone Tools Then and Now
flint knapping arrowheads chalk conching chocolate errett callahan scalpels obsidian chert agate geology stone tools
flint knapping arrowheads chalk conching chocolate errett callahan scalpels obsidian chert agate geology stone tools
Rock-Forming Mineral Formulas
Chemical formulas for the minerals that form the majority of rocks.
Chemical formulas for the minerals that form the majority of rocks.
Geologic Time Scale: Eons and Eras
The three eons and ten eras of the geologic time scale.
The three eons and ten eras of the geologic time scale.
Butte
A set of stereotypical buttes from the Four Corners region of the American Southwest.
A set of stereotypical buttes from the Four Corners region of the American Southwest.