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.
Landform Picture Gallery
The landform wing of the About Geology Picture Gallery.
The landform wing of the About Geology Picture Gallery.
Mineral Picture Gallery
The mineral wing of the About Geology Picture Gallery.
The mineral wing of the About Geology Picture Gallery.
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.
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.
Granite
Granite exemplified by a salt-and-pepper specimen from central California.
Granite exemplified by a salt-and-pepper specimen from central California.
Fossil Picture Gallery
Pictures of fossils in the About Geology Picture Gallery.
Pictures of fossils in 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.
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.
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.
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.
Gems to Minerals, Minerals to Gems
Mineral names and their corresponding gem names.
Mineral names and their corresponding gem names.
Glacier Picture Gallery
Pictures of glacial features and the processes of glaciers.
Pictures of glacial features and the processes of glaciers.
About the San Andreas Fault
Home page for everything about the San Andreas fault.
Home page for everything about the San Andreas fault.
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.
Gabbro
Gabbro is the plutonic equivalent of basalt.
Gabbro is the plutonic equivalent of basalt.
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.
Andesite
Andesite from the Sutter Buttes, California.
Andesite from the Sutter Buttes, California.
Pictures of Geologic Features and Processes
Pictures of geologic features and the processes of geology.
Pictures of geologic features and the processes of geology.
Diorite
Diorite is a plutonic rock, like granite without quartz.
Diorite is a plutonic rock, like granite without quartz.
About Quartz
Quartz alone and in rocks, with some notes.
Quartz alone and in rocks, with some notes.
Obsidian
Obsidian chunk from the Napa Valley volcanoes.
Obsidian chunk from the Napa Valley volcanoes.
Gold Nugget from Alaska
A genuine nugget of gold from an Alaska streambed, with notes.
A genuine nugget of gold from an Alaska streambed, with notes.
Chert
Chert pebbles from California.
Chert pebbles from California.
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.
Schist
Schist is a metamorphic rock that comes in many varieties.
Schist is a metamorphic rock that comes in many varieties.
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
Slate - Picture of Slate
Slate displays a range of earthy colors.
Slate displays a range of earthy colors.
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.
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.
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
Felsite
Felsite is the extrusive equivalent of granite.
Felsite is the extrusive equivalent of granite.
Shale
Shale or mudstone forms on the sea floor.
Shale or mudstone forms on the sea floor.
Agate
Agate is the name for the best quality of chert.
Agate is the name for the best quality of chert.
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.
Pumice
Pumice from a Californian volcano.
Pumice from a Californian volcano.
Rock Gypsum
Rock gypsum from a Nevada roadside.
Rock gypsum from a Nevada roadside.
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.
Plagioclase Feldspar
Plagioclase feldspar is a major rock-forming mineral.
Plagioclase feldspar is a major rock-forming mineral.
Conglomerate
Conglomerate is a sign of a vigorous environment.
Conglomerate is a sign of a vigorous environment.
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.
Marble
Marble is metamorphosed limestone.
Marble is metamorphosed limestone.
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.
How to Identify Minerals
First steps in mineral identification.
First steps in mineral identification.
Scoria
Scoria from a Californian volcano.
Scoria from a Californian volcano.
Serpentinite
Serpentinite, the California state rock, at the Oakland Museum of California.
Serpentinite, the California state rock, at the Oakland Museum of California.
Pegmatite
Pegmatite in a Colorado boulder.
Pegmatite in a Colorado boulder.
Porphyry
Porphyry is a widely varying type of igneous rock.
Porphyry is a widely varying type of igneous rock.
Biotite
Biotite is black mica, a common rock-forming mineral.
Biotite is black mica, a common rock-forming mineral.
Olivine
Olivine grain in Kilauea basalt.
Olivine grain in Kilauea basalt.
Geologic Map of Georgia
Georgia geologic map, at three different scales, created from the USGS data.
Georgia geologic map, at three different scales, created from the USGS data.
Syenite
Hand specimen of syenite.
Hand specimen of syenite.
Las Vegas Geology
Great rock shows are a sure thing around Las Vegas, Nevada.
Great rock shows are a sure thing around Las Vegas, Nevada.
Granodiorite
A polished slab of granodiorite from southeastern New Hampshire.
A polished slab of granodiorite from southeastern New Hampshire.
Rhyolite
Rhyolite from the Sutter Buttes, California.
Rhyolite from the Sutter Buttes, California.
Pyroxenite
Pyroxenite from the Feather River Ultramafics of the northern Sierra Nevada.
Pyroxenite from the Feather River Ultramafics of the northern Sierra Nevada.
Coquina
Coquina is a sedimentary rock made of shell fragments.
Coquina is a sedimentary rock made of shell fragments.
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.
Amphibolite
Amphibolite is metamorphosed basaltic rock.
Amphibolite is metamorphosed basaltic rock.
Chalcedony
Chalcedony is the microcrystalline form of quartz.
Chalcedony is the microcrystalline form of quartz.
Tuff
Tuff forms a cliff of tierra blanca in El Salvador.
Tuff forms a cliff of tierra blanca in El Salvador.
Calcite
Photo of Iceland spar calcite rhomb showing double refraction, with notes.
Photo of Iceland spar calcite rhomb showing double refraction, with notes.
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.
Siltstone
Siltstone, like sandstone but much finer grained.
Siltstone, like sandstone but much finer grained.
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.
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.
Phyllite
Photo of phyllite showing its micaceous sheen.
Photo of phyllite showing its micaceous sheen.
About Tsunamis
Tsunamis or tidal waves--whatever you call them, watch out.
Tsunamis or tidal waves--whatever you call them, watch out.
Thunder Egg
Thunder eggs form in volcanic sediments. Inside is solid agate.
Thunder eggs form in volcanic sediments. Inside is solid agate.
Talc
Talc, the softest mineral.
Talc, the softest mineral.
Coal
Coal is fossil peat.
Coal is fossil peat.
Alabaster
An image of alabaster, or fine-grained travertine.
An image of alabaster, or fine-grained travertine.
Dolomite Rock
A chunk of coarsely crystalline dolomite.
A chunk of coarsely crystalline dolomite.
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.
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.
What Is a Mineral?
Minerals meet four criteria, more or less strict.
Minerals meet four criteria, more or less strict.
Magnetite
Magnetite--a genuine lodestone up close.
Magnetite--a genuine lodestone up close.
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.
Blueschist
Blueschist, close up and deployed in a decorative setting.
Blueschist, close up and deployed in a decorative setting.
Eclogite
Eclogite, an extreme metamorphic rock from the mantle.
Eclogite, an extreme metamorphic rock from the mantle.
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.
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.
Tectonic Plate Boundaries, Western Hemisphere
Plate boundaries of the Western Hemisphere: divergent, convergent, and transform.
Plate boundaries of the Western Hemisphere: divergent, convergent, and transform.
Geologic Map of Alaska
Alaska geologic map, at three different scales.
Alaska geologic map, at three different scales.
Alluvial Fan
A wide alluvial fan debouches from a range in Montana.
A wide alluvial fan debouches from a range in Montana.
Serpentinite Gallery - Serpentinite from 'Earthquake Beach'
Serpentinite from the edge of the San Andreas fault south of Fort Ross.
Serpentinite from the edge of the San Andreas fault south of Fort Ross.
Global Seismic Hazard Map Index
First page of the Global Seismic Hazard Map gallery.
First page of the Global Seismic Hazard Map gallery.
Geologic Map of Missouri
Missouri geologic map, courtesy of the state geological survey
Missouri geologic map, courtesy of the state geological survey
Lapilli Tuff
Lapilli tuff in a California outcrop.
Lapilli tuff in a California outcrop.
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.
The Biggest Eruptions
The biggest eruptions in history and prehistory
The biggest eruptions in history and prehistory
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.
Migmatite
Migmatite is highly metamorphosed rock.
Migmatite is highly metamorphosed rock.
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.
Arkose
Arkose from the Fountain Formation of Colorado.
Arkose from the Fountain Formation of Colorado.
Geologic Map of Colorado
The great USGS Colorado geologic map, presented at full size.
The great USGS Colorado geologic map, presented at full size.
Diamond - Natural Diamond Specimen
A natural diamond grain from Congo shows rough crystal faces.
A natural diamond grain from Congo shows rough crystal faces.
Geologic Map of Michigan
Bedrock geologic map of Michigan, at three different scales, courtesy of the state of Michigan
Bedrock geologic map of Michigan, at three different scales, courtesy of the state of Michigan
Geologic Map of New York
New York geologic map, presented at four different scales.
New York geologic map, presented at four different scales.
"Herkimer Diamond" Quartz Crystal
Herkimer diamonds, the special double-ended stones from upstate New York.
Herkimer diamonds, the special double-ended stones from upstate New York.
Wacke or Graywacke
Wacke or graywacke is a sloppy kind of sandstone.
Wacke or graywacke is a sloppy kind of sandstone.
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
Greenstone
Greenstone in a California roadcut and outcrop.
Greenstone in a California roadcut and outcrop.
Serpentinite Gallery - Verd Antique or Serpentine Marble
The luscious green marble of builders is a serpentinite.
The luscious green marble of builders is a serpentinite.
Sedimentary Rock Gallery - Chert Nodule Interior
Interior of a chert nodule.
Interior of a chert nodule.
The Richter Scales
Nowadays, every earthquake magnitude scale is the Richter scale.
Nowadays, every earthquake magnitude scale is the Richter scale.
Perlite
Perlite from a young rhyolite dome.
Perlite from a young rhyolite dome.
Serpentinite Gallery - Serpentinite from Idria Ultramafic Body
Serpentinite of the Idria ultramafic body is a bright blue-green.
Serpentinite of the Idria ultramafic body is a bright blue-green.
Graphite - Graphite Specimen
Graphite in its raw form.
Graphite in its raw form.
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.
Serpentinite Gallery - Bastite, Serpentinitized Pyroxene
Bastite is the name given to pyroxene replaced by serpentine.
Bastite is the name given to pyroxene replaced by serpentine.
Cement and Concrete
Cement is an artificial stone--or maybe lava.
Cement is an artificial stone--or maybe lava.
Amethyst
Amethyst, the purple variety of quartz, is shown here as a geode crust.
Amethyst, the purple variety of quartz, is shown here as a geode crust.
Mesa (in sedimentary rocks)
This Utah mesa displays the basic characteristics of the landform: flat top, steep sides, horizontal sedimentary layers.
This Utah mesa displays the basic characteristics of the landform: flat top, steep sides, horizontal sedimentary layers.
Zen Rock Garden
A quiet zen rock garden suggests a landscape with the simplest means.
A quiet zen rock garden suggests a landscape with the simplest means.
Geodes (Before)
Two small unbroken geodes offer the promise of glittering guts.
Two small unbroken geodes offer the promise of glittering guts.
What Are Fossils?
Fossils are precious gifts from the geologic past.
Fossils are precious gifts from the geologic past.
The Tokai Earthquake of 20xx
Japan has been preparing for it for over 25 years.
Japan has been preparing for it for over 25 years.
Serpentinite Gallery - Vermont Serpentinite Closeup
Closeup of the faulted surface of a Vermont serpentinite.
Closeup of the faulted surface of a Vermont serpentinite.
Geologic Tools of the Trade
The humble tools adapted from tradesmen's equipment, plus the artist's eye and sketchpad, have served geologists well for centuries.
The humble tools adapted from tradesmen's equipment, plus the artist's eye and sketchpad, have served geologists well for centuries.
Tourmaline - Schorl
Schorl, black tourmaline, displays its typical crystal form.
Schorl, black tourmaline, displays its typical crystal form.
Serpentinite Gallery - Acicular Crystals in Serpentinite
Needlelike crystals in a serpentinite vein near Lake Berryessa, California.
Needlelike crystals in a serpentinite vein near Lake Berryessa, California.
Serpentinite Gallery - Serpentinite, Ring Mountain Preserve
A closeup of high-grade serpentinite at the Ring Mountain Preserve.
A closeup of high-grade serpentinite at the Ring Mountain Preserve.
Hornblende
A hornblende pocket in Sierra Nevada granite.
A hornblende pocket in Sierra Nevada granite.
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.
Canyon
The Grand Canyon of the Yellowstone River cuts a mighty swathe through the thick volcanic deposits of northwestern Wyoming.
The Grand Canyon of the Yellowstone River cuts a mighty swathe through the thick volcanic deposits of northwestern Wyoming.
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.
Pyrite
Pyrite grains and crystals in many settings.
Pyrite grains and crystals in many settings.
Opal
Extreme close-ups of a 'Christmas tree' opal, with notes.
Extreme close-ups of a 'Christmas tree' opal, with notes.
Serpentinite Gallery - Light and Dark Serpentinite, Sierra Nevada
Light and dark serpentinite at the same locality.
Light and dark serpentinite at the same locality.
Geology and Society Picture Gallery
Where geology overlaps the wider culture.
Where geology overlaps the wider culture.
Geologic Map of Mississippi
Mississippi geologic map, courtesy of the Gulf Coast Program.
Mississippi geologic map, courtesy of the Gulf Coast Program.
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.
Ammonoid or Ammonite
Miniature ammonoid fossil, emblem of the Cretaceous.
Miniature ammonoid fossil, emblem of the Cretaceous.
Escarpment
Abert Rim is one of North America's grandest escarpments.
Abert Rim is one of North America's grandest escarpments.
Gypsum
Clear specimens and desert roses composed of gypsum.
Clear specimens and desert roses composed of gypsum.
Serpentinite Gallery - Serpentinite Hand Specimen, Lake Berryessa
A lovely hand specimen of California serpentinite.
A lovely hand specimen of California serpentinite.
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.
Brachiopod
A typical brachiopod fossil.
A typical brachiopod fossil.
Geologic Map of New Mexico
New Mexico geologic map, courtesy of the New Mexico Bureau of Mines and Mineral Resources
New Mexico geologic map, courtesy of the New Mexico Bureau of Mines and Mineral Resources
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.
Anticline
Anticline.
Anticline.
Coal in a Nutshell
Introducing coal: how it forms, what's in it, what it tells us.
Introducing coal: how it forms, what's in it, what it tells us.
Serpentinite Gallery - Serpentinite, Feather River Ultramafic Complex, California
Mottled green serpentinite in the Sierra Nevada.
Mottled green serpentinite in the Sierra Nevada.
Natural Asphalt
Natural asphalt from the McKittrick oil seep.
Natural asphalt from the McKittrick oil seep.
Geologic Map of Utah
Utah geologic map, at four different scales with notes.
Utah geologic map, at four different scales with notes.