Geology: Most Popular Articles
These articles are the most popular over the last month.
Rock Identification Tables
Identify 43 of the most common rock types: igneous, sedimentary and metamorphic.
Identify 43 of the most common rock types: igneous, sedimentary and metamorphic.
Gneiss
Gneiss is a major metamorphic rock type from regional metamorphism.
Gneiss is a major metamorphic rock type from regional metamorphism.
Common Rock Densities
Density, or specific gravity, of common rock types.
Density, or specific gravity, of common rock types.
Mineral Pictures Index
Master guide to pictures of rock-forming, accessory, and rare or notable minerals.
Master guide to pictures of rock-forming, accessory, and rare or notable minerals.
Rock Picture Index
Master guide to rock pictures and descriptions on About.com Geology.
Master guide to rock pictures and descriptions on About.com Geology.
Quartzite
Quartzite is a major metamorphic rock type from regional metamorphism.
Quartzite is a major metamorphic rock type from regional metamorphism.
Basalt
Basalt is one of the major igneous rock types.
Basalt is one of the major igneous rock types.
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.
About Granite
Granite is the signature rock of the continents.
Granite is the signature rock of the continents.
Schist
Schist is a major metamorphic rock type from regional metamorphism.
Schist is a major metamorphic rock type from regional metamorphism.
Slate
Slate is a major metamorphic rock type from regional metamorphism.
Slate is a major metamorphic rock type from regional metamorphism.
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.
Marble
Marble is a major metamorphic rock type from regional metamorphism.
Marble is a major metamorphic rock type from regional metamorphism.
Granite
Granite is one of the major igneous rock types.
Granite is one of the major igneous rock types.
Green Minerals
A guide to the most common and significant green and greenish minerals.
A guide to the most common and significant green and greenish minerals.
Obsidian
Obsidian is one of the major igneous rock types.
Obsidian is one of the major igneous rock types.
Diorite
Diorite is one of the major igneous rock types.
Diorite is one of the major igneous rock types.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
The major igneous rock types, plutonic, intrusive and extrusive.
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.
Mohs Hardness Scale
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
Sandstone
Sandstone is one of the major types of sedimentary rocks.
Sandstone is one of the major types of sedimentary rocks.
Serpentinite
Serpentinite is a major metamorphic rock type from regional metamorphism.
Serpentinite is a major metamorphic rock type from regional metamorphism.
About Sandstone
Sandstone is sand cemented together into rock.
Sandstone is sand cemented together into rock.
Shale
Shale is one of the major types of sedimentary rocks.
Shale is one of the major types of sedimentary rocks.
Limestone
Limestone is one of the major types of sedimentary rocks.
Limestone is one of the major types of sedimentary rocks.
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.
Gabbro
Gabbro is one of the major igneous rock types.
Gabbro is one of the major igneous rock types.
Pegmatite
Pegmatite is one of the major igneous rock types.
Pegmatite is one of the major igneous rock types.
Siltstone
Siltstone is one of the major types of sedimentary rocks.
Siltstone is one of the major types of sedimentary rocks.
Global Seismic Hazard Maps
The United Nations' global map of seismic hazard
The United Nations' global map of seismic hazard
Pumice
Pumice is one of the major igneous rock types.
Pumice is one of the major igneous rock types.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism.
Phyllite is a major metamorphic rock type from regional metamorphism.
Scoria
Scoria is one of the major igneous rock types.
Scoria is one of the major igneous rock types.
Chemical Weathering
A short explanation of chemical weathering.
A short explanation of chemical weathering.
Chert
Chert is one of the major types of sedimentary rocks.
Chert is one of the major types of sedimentary rocks.
Andesite
Andesite is one of the major igneous rock types.
Andesite is one of the major igneous rock types.
Peridotite
Peridotite is one of the major igneous rock types.
Peridotite is one of the major igneous rock types.
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks.
Wacke or graywacke is one of the major types of sedimentary rocks.
The Earth's 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.
How to Identify Minerals
First steps in mineral identification.
First steps in mineral identification.
How to Look at a Rock
Notes on the most basic operation in geology.
Notes on the most basic operation in geology.
The Most Common Mineral
This question has several answers, depending on what a mineral is and what part of the Earth we're talking about.
This question has several answers, depending on what a mineral is and what part of the Earth we're talking about.
Where to Find Rocks & Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
Rocks and minerals can be found everywhere, but there is a learning process involved.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
Exfoliation
How big rock domes peel off in shells.
How big rock domes peel off in shells.
Felsite
Felsite is one of the major igneous rock types.
Felsite is one of the major igneous rock types.
Sedimentary Rock Types
The major types of sedimentary rocks.
The major types of sedimentary rocks.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks.
Conglomerate is one of the major types of sedimentary rocks.
Porphyry
Porphyry is one of the major igneous rock types.
Porphyry is one of the major igneous rock types.
Arkose
Arkose is one of the major types of sedimentary rocks.
Arkose is one of the major types of sedimentary rocks.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Pictures of fossils, part of the About.com Geology gallery of images.
Syenite
Syenite is one of the major igneous rock types.
Syenite is one of the major igneous rock types.
Dunite
Dunite is a plutonic rock consisting of olivine.
Dunite is a plutonic rock consisting of olivine.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism.
Migmatite is a major metamorphic rock type from regional metamorphism.
Pyroxenite
Pyroxenite is one of the major igneous rock types.
Pyroxenite is one of the major igneous rock types.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar.
Tonalite is a felsic plutonic rock without alkali feldspar.
Breccia
Breccia is one of the major types of sedimentary rocks.
Breccia is one of the major types of sedimentary rocks.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism.
Grenstone is a major metamorphic rock type from regional metamorphism.
Granodiorite
Granodiorite is one of the major igneous rock types.
Granodiorite is one of the major igneous rock types.
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.
Blue and Purple Minerals
A guide to the most common and significant blue and purple minerals.
A guide to the most common and significant blue and purple minerals.
Dolomite Rock or Dolostone
Dolomite or dolostone is one of the major types of sedimentary rocks.
Dolomite or dolostone is one of the major types of sedimentary rocks.
Quartz
Quartz is classified as a rock-forming mineral.
Quartz is classified as a rock-forming mineral.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism.
Hornfels is a major metamorphic rock type from contact metamorphism.
Tuff
Tuff is one of the major igneous rock types.
Tuff is one of the major igneous rock types.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism.
Soapstone is a major metamorphic rock type from regional metamorphism.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
Amphibolite is one of the major metamorphic rock types.
About the San Andreas Fault
Home page for everything about the San Andreas fault.
Home page for everything about the San Andreas fault.
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 is one of the major igneous rock types.
Rhyolite is one of the major igneous rock types.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks.
Rock gypsum is one of the major types of sedimentary rocks.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism.
Greenschist is a major metamorphic rock type from regional metamorphism.
Coquina
Coquina is one of the major types of sedimentary rocks.
Coquina is one of the major types of sedimentary rocks.
Black Minerals
A guide to the most common and significant black minerals.
A guide to the most common and significant black minerals.
Komatiite
Komatiite is a rare and ancient ultramafic lava.
Komatiite is a rare and ancient ultramafic lava.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism.
Eclogite is a major metamorphic rock type from regional metamorphism.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism.
Mylonite is a major metamorphic rock type from mechanical metamorphism.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism.
Blueschist is a major metamorphic rock type from regional metamorphism.
About Quartz
Quartz is essential to the land as we know it.
Quartz is essential to the land as we know it.
Rock Salt
Rock salt is one of the major types of sedimentary rocks.
Rock salt is one of the major types of sedimentary rocks.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types.
Quartz monzonite is one of the major igneous rock types.
Landform Picture Index
Find and see geological landforms at About.com Geology.
Find and see geological landforms at About.com Geology.
Sumatra 26 Dec 2004 M9.3
The greatest earthquake in 40 years killed 300,000 people.
The greatest earthquake in 40 years killed 300,000 people.
Coal
Coal is one of the major types of sedimentary rocks.
Coal is one of the major types of sedimentary rocks.
Sediment Grain Size Categories
Sediment grades and grain sizes listed from boulders down to clay.
Sediment grades and grain sizes listed from boulders down to clay.
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.
Anorthosite
Anorthosite is one of the major igneous rock types.
Anorthosite is one of the major igneous rock types.
Perlite
Perlite is one of the major igneous rock types.
Perlite is one of the major igneous rock types.
What Are Minerals?
Minerals meet four criteria, more or less strict.
Minerals meet four criteria, more or less strict.
JMA Earthquake Scale
Details of the modern Japanese seismic intensity scale.
Details of the modern Japanese seismic intensity scale.
Latite
Latite is the extrusive equivalent of monzonite.
Latite is the extrusive equivalent of monzonite.
About Subduction in Plate Tectonics
Basics of plate tectonics: introduction to subduction.
Basics of plate tectonics: introduction to subduction.
Argillite
A lightly metamorphosed claystone also called pipestone.
A lightly metamorphosed claystone also called pipestone.
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.
Quartz and Silica Minerals Gallery
Get familiar with quartz.
Get familiar with quartz.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states.
Geologic map of Texas, part of a set of all 50 states.
The Rock-Forming Minerals
A handful of very abundant minerals account for the great majority of the Earth's rocks.
A handful of very abundant minerals account for the great majority of the Earth's rocks.
Amphibole Minerals
Gallery of amphibole minerals.
Gallery of amphibole minerals.
Provincial Time Terms
Not all geologic time units are settled and universal.
Not all geologic time units are settled and universal.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
The five ways we track the motion of the lithospheric plates.
Pictures of Geologic Features and Processes
Pictures of geologic features and the processes of geology.
Pictures of geologic features and the processes of geology.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks.
Banded iron formation or BIF is one of the major types of sedimentary rocks.
About the Earth's Core
How we study the Earth's core and what it may be made of.
How we study the Earth's core and what it may be made of.
Mechanical Weathering
A short explanation of mechanical weathering.
A short explanation of mechanical weathering.
Olivine
Olivine is an important rock-forming mineral.
Olivine is an important rock-forming mineral.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Photos of the types of erupted igneous rocks.
Biotite
Biotite is an iron-rich member of the mica minerals.
Biotite is an iron-rich member of the mica minerals.
QAP Diagram for Plutonic Rocks
QAP ternary diagram showing IUGS classification of phaneritic igneous rocks.
QAP ternary diagram showing IUGS classification of phaneritic igneous rocks.
Weathering
A short description of weathering.
A short description of weathering.
Actinolite
Actinolite is a major amphibole mineral.
Actinolite is a major amphibole mineral.
What Are Fossils?
Fossils are precious gifts from the geologic past.
Fossils are precious gifts from the geologic past.
Diatomite
Picture and notes about the sedimentary rock diatomite.
Picture and notes about the sedimentary rock diatomite.
Cement and Concrete
Cement is an artificial stone--or maybe lava.
Cement is an artificial stone--or maybe lava.
Diamictite
Diamictite is a messy rock that is not quite conglomerate.
Diamictite is a messy rock that is not quite conglomerate.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states.
Geologic map of North Carolina, part of a set of all 50 states.
Parks that allow fossil collecting
Public parks in the United States where you can collect fossils legally.
Public parks in the United States where you can collect fossils legally.
Peat
Peat is one of the major types of sedimentary rocks.
Peat is one of the major types of sedimentary rocks.
Travertine
Travertine is one of the major types of sedimentary rocks.
Travertine is one of the major types of sedimentary rocks.
About Plate Tectonics
Start here to learn the basics of plate tectonics.
Start here to learn the basics of plate tectonics.
Claystone
Claystone is a type of sedimentary rock.
Claystone is a type of sedimentary rock.
Current Earthquakes
Directions to information and data from earthquakes as fast as possible.
Directions to information and data from earthquakes as fast as possible.
Cataclasite
Cataclasite is a major metamorphic rock type from mechanical metamorphism.
Cataclasite is a major metamorphic rock type from mechanical metamorphism.
Geologic Time Scale: Phanerozoic Eon
Eras, periods and epochs of the Phanerozoic, part of the official geologic time scale.
Eras, periods and epochs of the Phanerozoic, part of the official geologic time scale.
Alabaster
Alabaster or massive gypsum rock is one of the sedimentary rocks.
Alabaster or massive gypsum rock is one of the sedimentary rocks.
Index Fossils
The concept of index fossils is important in geologic dating.
The concept of index fossils is important in geologic dating.
Reading Geologic Maps
Understanding geologic maps starts with topography.
Understanding geologic maps starts with topography.
Plates and Their Boundaries
Details of the world's major tectonic plates and their boundaries.
Details of the world's major tectonic plates and their boundaries.
Granitoids
How geologists sort out granite from the rocks that look like it.
How geologists sort out granite from the rocks that look like it.
Oklahoma Geologic Map
Geologic map of Oklahoma, part of a set of all 50 states.
Geologic map of Oklahoma, part of a set of all 50 states.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
Geologic maps of all 50 U.S. states.
Gemstone-Mineral Tables
Mineral names and their corresponding gemstone names.
Mineral names and their corresponding gemstone names.
Obsidian Gallery
Obsidian is an extreme variety of igneous rock with a glassy texture.
Obsidian is an extreme variety of igneous rock with a glassy texture.
Talc
Talc is one of the silicate minerals.
Talc is one of the silicate minerals.
Geologic Time Scale: Eons, Eras and Periods
The periods of geologic time, part of the official geologic time scale.
The periods of geologic time, part of the official geologic time scale.
Igneous Rock Classification Diagrams
Diagrams showing IUGS classification of phaneritic and aphanitic igneous rocks.
Diagrams showing IUGS classification of phaneritic and aphanitic igneous rocks.
Basic Plate Map
The classic basic map from the U.S. Geological Survey.
The classic basic map from the U.S. Geological Survey.
Michigan Geologic Map
Geologic map of Michigan, part of a set of all 50 states.
Geologic map of Michigan, part of a set of all 50 states.
About Coltan
High prices for tantalite create devastation in central Africa.
High prices for tantalite create devastation in central Africa.
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.
Agate
Agate is a rock made of chalcedony or cryptocrystalline quartz.
Agate is a rock made of chalcedony or cryptocrystalline quartz.
Calderas - World's Largest Calderas
Table of the world's largest known calderas: chinati mountains kari kari supervolcanoes awasa taupo new zealand
Table of the world's largest known calderas: chinati mountains kari kari supervolcanoes awasa taupo new zealand
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Minerals with metallic luster are easy to learn to identify.
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.
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.
Sea Arch, California
Sea arches are a type of erosional landform.
Sea arches are a type of erosional landform.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks.
Natural asphalt is one of the major types of sedimentary rocks.
Minerals A-Z
A-to-Z list of minerals shown on About.com Geology.
A-to-Z list of minerals shown on About.com Geology.
Red and Pink Minerals
A guide to the most common and significant red and pink minerals.
A guide to the most common and significant red and pink minerals.
Sedimentary Rock Gallery
An assortment of sedimentary rocks, from fine to coarse grained.
An assortment of sedimentary rocks, from fine to coarse grained.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
What you need to know about the lithosphere.