Geology: Most Popular Articles

Rock Picture Gallery
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.

Mineral 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.

Granite
Granite exemplified by a salt-and-pepper specimen from central California.

Sandstone
A large boulder of sandstone, with visible layering features, sits in a Berkeley landscaping yard.

Basalt
Basalt from Hawaii with vesicles and olivine grains.

About Sedimentary Rocks
The second of the three great rock classes is introduced with photos.

Limestone
Limestone appears in a New York roadcut.

Obsidian
Obsidian chunk from the Napa Valley volcanoes.

Landform Picture Gallery
The landform wing of the About Geology Picture Gallery.

The Richter Scales
Nowadays, every earthquake magnitude scale is the Richter scale.

Slate
Slate sits in a stoneyard.

Seismic Hazard Map, China
The China part of the Global Seismic Hazard Map of 1999.

Plate Tectonics - The World's Crustal Plates
The Earth's crustal plates, from the U.S. Geological Survey

About Metamorphic Rocks
The three great rock classes--igneous, sedimentary and metamorphic--are introduced with photos, finishing with metamorphic.

About the Earth's Core
How we study the Earth's core and what it's made of.

Fossil Picture Gallery
Pictures of fossils in the About Geology Picture Gallery.

Gabbro
Gabbro is the plutonic equivalent of basalt.

Schist
Schist is a metamorphic rock that comes in many varieties.

About the San Andreas Fault
Home page for everything about the San Andreas fault.

The Mohs Scale of Relative Mineral Hardness
The ten-mineral Mohs scale of relative hardness, based on what scratches what.

Andesite
Andesite from the Sutter Buttes, California.

Chert
Chert pebbles from California.

Quartzite
A boulder of tough, solid quartzite sits by a Las Vegas building.

About Quartz
Quartz alone and in rocks, with some notes.

Glacier Picture Gallery
Pictures of glacial features and the processes of glaciers.

Geologic Map of California
California geologic map, at four different scales.

Shale
Shale or mudstone forms on the sea floor.

Global Seismic Hazard Map Index
First page of the Global Seismic Hazard Map gallery.

Aa Lava
A glowing flow of aa lava advances from the Puu Oo eruption on Hawaii island.

Diorite
Diorite is a plutonic rock, like granite without quartz.

Gneiss
A fresh boulder of meat-colored Pinto Gneiss, in Joshua Tree National Park, shows the characteristics of this metamorphic rock type.

Pictures of Geologic Features and Processes
Pictures of geologic features and the processes of geology.

Pumice
Pumice from a Californian volcano.

Agate
Agate is the name for the best quality of chert.

Geologic Map of Texas
Texas geologic map, courtesy of the state bureau of economic geology

Serpentinite
Serpentinite, the California state rock, at the Oakland Museum of California.

Gems to Minerals, Minerals to Gems
Mineral names and their corresponding gem names.

Felsite
Felsite is the extrusive equivalent of granite.

Marble
Marble is metamorphosed limestone.

1906 San Francisco Earthquake
The Great San Francisco Earthquake was the stuff of legend, but it really happened.

Siltstone
Siltstone, like sandstone but much finer grained.

Scoria
Scoria from a Californian volcano.

Porphyry
Porphyry is a widely varying type of igneous rock.

What Is Geology?
The whole of Earth sciences, compressed to a nutshell.

Conglomerate
Conglomerate is a sign of a vigorous environment.

Phyllite
Photo of phyllite showing its micaceous sheen.

The Tibetan Plateau
The largest highest place on Earth is a showcase of plate tectonics.

Tuff
Tuff forms a cliff of tierra blanca in El Salvador.

Coal
Coal is fossil peat.

Amphibolite
Amphibolite is metamorphosed basaltic rock.

Syenite
Hand specimen of syenite.

Pegmatite
Pegmatite in a Colorado boulder.

Breccia
Breccia takes many forms; this photo shows a pebble of a fault breccia.

Dolomite Rock
A chunk of coarsely crystalline dolomite.

Rock Gypsum
Rock gypsum from a Nevada roadside.

Pyroxenite
Pyroxenite from the Feather River Ultramafics of the northern Sierra Nevada.

About the Earth's Mantle
A look at six different aspects of the Earth's mantle.

Migmatite
Migmatite is highly metamorphosed rock.

Rhyolite
Rhyolite from the Sutter Buttes, California.

Gypsum
Clear specimens and desert roses composed of gypsum.

Coquina
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.

Solar Studies
Studying the Sun tells a lot about the Earth.

Thunder Egg
Thunder eggs form in volcanic sediments. Inside is solid agate.

Plate Tectonics in a Nutshell
A simple starting point for the basics of plate tectonics.

Wacke or Graywacke
Wacke or graywacke is a sloppy kind of sandstone.

Mountain Pictures - California Peaks
Great pictures of great Californian mountains.

Stop 5, the Glory Hole
An overflow structure helps drain Lake Berryessa in northern California.

Granodiorite
A polished slab of granodiorite from southeastern New Hampshire.

Arkose
Arkose from the Fountain Formation of Colorado.

Eclogite
Eclogite, an extreme metamorphic rock from the mantle.

Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.

Deaths from Tsunamis, by Ocean
The deadliest tsunamis recorded in each ocean basin.

The Biggest Eruptions
The biggest eruptions in history and prehistory

About Tsunamis
Tsunamis or tidal waves--whatever you call them, watch out.

Tectonic Plate Boundaries, Eastern Hemisphere
Plate boundaries of the Eastern Hemisphere: divergent, convergent, and transform.

Pahoehoe Lava
A flow of fresh hot pahoehoe lava smothers an old Hawaiian footpath.

Earth Formation in a Nutshell
The straight story of how Earth began, as today's geologists tell it.

Banded Iron Formation
Australian 'folded tiger iron' is a spectacular variety of banded iron formation.

Muscovite
Muscovite or white mica, a nice hand specimen from New York state.

Recipes for Volcanoes
Moviemakers and scientists have gone beyond vinegar and baking soda.

The Tokai Earthquake of 20xx
Japan has been preparing for it for over 25 years.

Geologic Map of Alabama
Alabama geologic map, courtesy of the state geological survey

Plagioclase Feldspar
Plagioclase feldspar is a major rock-forming mineral.

Calcite
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.

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.

Articles on Earthquakes
Features about earthquakes, seismology, and related phenomena from your About Geology Guide.

Tectonic Plates with Topography, Eastern Hemisphere
Topography of the Eastern Hemisphere with tectonic plate boundaries.

Lapilli Tuff
Lapilli tuff in a California outcrop.

Earthquake Statistics
A graph displays the numbers of quakes of different magnitudes.

Alabaster
An image of alabaster, or fine-grained travertine.

Geodes (Before)
Two small unbroken geodes offer the promise of glittering guts.

Greenstone
Greenstone in a California roadcut and outcrop.

Blueschist
Blueschist, close up and deployed in a decorative setting.

Potassium or Alkali Feldspar - Microcline (Amazonite)
Bright-green amazonite is an easy-to-recognize variety of microcline, a potassium or alkali feldspar.

Chalcedony
Chalcedony is the microcrystalline form of quartz.

Lisbon Earthquake, 1 November 1755
Lisbon earthquake of 1 November 1755, images and notes.

Geologic Map of New York
New York geologic map, presented at four different scales.

Geologic Map of Colorado
The great USGS Colorado geologic map, presented at full size.

Geologic Time Scale: The Cenozoic Era
Ages, epochs and periods of the Cenozoic Era, part of the geologic time scale.

Greenschist
Greenschist, a dark-green silicate rock formed by metamorphism of old seafloor.

Magnetite
Magnetite--a genuine lodestone up close.

Zen Rock Garden
A quiet zen rock garden suggests a landscape with the simplest means.

Peat
Peat is the precursor of coal.

Actinolite
Actinolite, a green silicate mineral formed by the metamorphism of old seafloor.

Alluvial Fan
A wide alluvial fan debouches from a range in Montana.

The Global Seismic Hazard Map
The first map to show the entire world's seismic hazard consistently is out--and it's all here on this site.

Talc
Talc, the softest mineral.

Asphalt
Asphalt from the McKittrick oil seep.

Geologic Time Scale: Eons and Eras
The three eons and ten eras of the geologic time scale.

Graphite - Graphite Specimen
Graphite in its raw form.

Diamond - Natural Diamond Specimen
A natural diamond grain from Congo shows rough crystal faces.

Olivine
Olivine grain in Kilauea basalt.

Fulgurite
A small Moroccan fulgurite records a lightning strike on sand.

Dolomite
Closeup of granular dolomite.

Mercalli Earthquake Intensity Scale
The modified Mercalli intensity scale rates the impact of quakes from I to XII.

Biotite
Biotite is black mica, a common rock-forming mineral.

Geology Wallpaper Images - Rock Closeups
A selection of wallpaper images of rocks in loving detail.

Travertine
Travertine, a low-density form of limestone.

Brachiopod
A typical brachiopod fossil.

Geologic Map of Chile
Geologic map of Chile.

Halite
Halite in three forms: rock salt, halite crystals and table salt.

Valley Glacier - or Mountain or Alpine Glacier
Bucher Glacier, a typical valley - or mountain or alpine - glacier.

Kettle
Kettles dot the outwash plain of Bering Glacier in Alaska.

How to Identify Minerals
First steps in mineral identification.

Geologic Map of Michigan
Bedrock geologic map of Michigan, at three different scales, courtesy of the state of Michigan

What Is a Mineral?
Minerals meet four criteria, more or less strict.

Pyrite
Pyrite grains and crystals in many settings.

Mica Schist
A dark mica schist from Manhattan.

Geologic Map of Washington State
Washington state geologic map, at three different scales, presented with notes.

Earthquake Intensities
Intensity scales measure how bad a quake is, on a scale from I to XII.

Geologic Time Scale: Precambrian Time
The Precambrian part of the geologic time scale.

Gold Nugget
Gold nugget, in the gallery of minerals with metallic luster.

Conflict Diamonds
The problem of clandestine gems has no geological solution.

Geologic Map of New Mexico
New Mexico geologic map, courtesy of the New Mexico Bureau of Mines and Mineral Resources

Geology Desktop Wallpaper Pictures
Free 800x600, 1024x768 and 1280x1024 geology pictures for your computer's desktop wallpaper.

"Herkimer Diamond" Quartz Crystal
Herkimer diamonds, the special double-ended stones from upstate New York.

What Are Fossils?
Fossils are precious gifts from the geologic past.

Ruby - Mineral Specimen of Ruby
A ruby pebble from India.

Geologic Map of Arkansas
Arkansas geologic map, presented at four different scales with notes.

Sumatra 26 Dec 2004 M9.3
The greatest earthquake in 40 years killed 300,000 people.

Earthquake Lights
A new theory of earthquake lights looks promising

Geologic Map of Georgia
Georgia geologic map, at three different scales, created from the USGS data.

Anticline
Anticline.

Geologic Map of Alaska
Alaska geologic map, at three different scales.

Chondrite Meteorite
Chondrites are the most common kind of meteorite.

Amethyst
Amethyst, the purple variety of quartz, is shown here as a geode crust.