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Geology: Most Popular Articles

These articles are the most popular over the last month.
Identify Almost Any Rock with This Table
Identify 43 of the most common rock types: igneous, sedimentary and metamorphic.
See the Densities of the Most Common Rock Types
Density, or specific gravity, of common rock types.
What Is Chemical Weathering?
A short explanation of chemical weathering.
Use This Master Index of Rock Pictures
My master alphabetical guide to igneous, sedimentary and metamorphic rock pictures.
Why the Earth's Crust Is So Important
The Earth's crust is exceptionally important, and not just because we live on it.
What to Know About Sedimentary Rocks
Introducing sedimentary rocks, second of the three great rock classes (along with igneous and metamorphic rocks).
6 Things to Know About the Earth's Mantle
A six-part look at the basics of the Earth's mantle, the part between the crust and the core.
What Makes Metamorphic Rocks Special
Most of the thousands of rare minerals known to science occur in metamorphic rocks, which are formed by great heat and pressure. Introducing
The Most Common Green Minerals in Nature
A guide to the most common and significant green and greenish minerals.
What to Know About Igneous Rocks
Introducing igneous rocks, first of the three great rock classes (along with sedimentary and metamorphic rocks).
What Is My Blue or Purple Mineral?
A guide to the most common and significant blue and purple minerals.
Identify Typical Minerals with This Master...
My master guide to annotated pictures to help you identify minerals: typical examples of rock-forming, accessory, and rare or notable minerals.
Schist
Schist is a major metamorphic rock type from regional metamorphism. Page 15.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
Gneiss
Gneiss is a major metamorphic rock type from regional metamorphism. Page 6.
10 Steps to Help You Identify Any Mineral
Mineral identification starts with picking a good specimen.
Serpentinite
Serpentinite is a major metamorphic rock type from regional metamorphism. Page 16.
Quartzite
Quartzite is a major metamorphic rock type from regional metamorphism. Page 14.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Why Granite is the Signature Rock of Earth
Granite is the signature rock of the continents. Here are the basics of this important stone.
Index Fossils: The Key to Telling Deep Time
The concept of index fossils is the very basis of geologic dating.
Coquina
Coquina is one of the major types of sedimentary rocks. Page 11.
Diorite
Diorite is one of the major igneous rock types. Page 4.
Siltstone
Siltstone is one of the major types of sedimentary rocks. Page 24.
Fast Links for Real-Time Info on Current...
Directions to information and data from earthquakes as fast as possible.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
Map of Plates and Their Boundaries
Details of the world's major tectonic plates and their boundaries.
Pumice
Pumice is one of the major igneous rock types. Page 18.
What Is the Most Common Mineral on Earth?
This question has several answers, depending on what a mineral is and what part of the Earth we're talking about.
Obsidian
Obsidian is one of the major igneous rock types. Page 13.
Granite
Granite is one of the major igneous rock types. Page 8.
What a Black Mineral Is Most Likely to Be
A guide to the most common and significant black minerals.
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
Where to Look for Rocks and Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
Basalt
Basalt is one of the major igneous rock types. Page 3.
Sedimentary Rock Types
The major types of sedimentary rocks.
Sandstone: What It Is and What It Tells Us
Sandstone is sand cemented together into rock.
Marble
Marble is a major metamorphic rock type from regional metamorphism. Page 10.
Scoria
Scoria is one of the major igneous rock types. Page 22.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar. Page 24.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
How to Look at a Rock Like a Geologist
Notes on the most basic operation in geology.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Syenite
Syenite is one of the major igneous rock types. Page 23.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
Exfoliation
How big rock domes peel off in shells. Page 6.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
Felsite
Felsite is one of the major igneous rock types. Page 6.
Andesite
Andesite is one of the major igneous rock types.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism. Page 8.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks. Page 15.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
More Than 50 Different Landforms in Pictures
Find and see geological landforms at About.com Geology.
Sandstone
Sandstone is one of the major types of sedimentary rocks. Page 22.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism. Page 11.
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
Limestone
Limestone is one of the major types of sedimentary rocks. Page 17.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
Mechanical Weathering
A short explanation of mechanical weathering.
Claystone
Claystone is a type of sedimentary rock. Page 8.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
Where Are the Greatest Earthquake Threats in...
The United Nations' global map of seismic hazard
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Dolomite Rock or Dolostone
Dolomite or dolostone is one of the major types of sedimentary rocks. Page 14.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks. Page 20.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism. Page 12.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks. Page 10.
Tuff
Tuff is one of the major igneous rock types. Page 26.
Anorthosite
Anorthosite is one of the major igneous rock types. Page 2.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
The Size Divisions of Sediment Particles
The grain sizes of sediments and sedimentary rocks are a matter of great interest to geologists. Here is a guide to sediment grades and grain sizes.
California Geologic Map
Geologic map of California, part of a set of all 50 states. Page 5.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states. Page 33.
Diamictite
Diamictite is a messy rock that is not quite conglomerate. Page 12.
How to Use the Mohs Hardness Scale to Identify...
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
Plutonic Rocks
Plutonic rocks defined and explained.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
Sizes of Tectonic or Lithospheric Plates
Table listing the lithosphere's tectonic plates by oder of size.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
Rock Salt
Rock salt is one of the major types of sedimentary rocks. Page 21.
Peat
Peat is one of the major types of sedimentary rocks. Page 18.
Coal
Coal is one of the major types of sedimentary rocks. Page 9.
Utah Geologic Map
Geologic map of Utah, part of a set of all 50 states. Page 44.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
What Is My Yellow Mineral?
A guide to the most common and significant yellow minerals.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
The Scientific Definition of a Mineral
Minerals meet four criteria, more or less strict.
Argillite
A lightly metamorphosed claystone also called pipestone. Page 2.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
Georgia Geologic Map
Geologic map of Georgia, part of a set of all 50 states. Page 10.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
Mineral Pictures A to Z
A-to-Z list of minerals shown on About.com Geology.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks. Page 3.
Earthquakes - The Basics in a Nutshell
Start here for the seismic basics: faults that cause earthquakes, types of seismic waves, damages they cause and more.
About Subduction in Plate Tectonics
Basics of plate tectonics: introduction to subduction.
Translate Names Between Gemstones and Minerals
Big list of mineral names and their corresponding gemstone names.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks. Page 4.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Porcellanite
Porcellanite is a subtle sedimentary rock type. Page 19.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
About Convergent Zones in Plate Tectonics
Basics of plate tectonics: convergent zones are where plates come together.
North Dakota Geologic Map
Geologic map of North Dakota, part of a set of all 50 states. Page 34.
Cataclasite
Cataclasite is a major metamorphic rock type from mechanical metamorphism. Page 4.
Learn to Read a Geologic Map
What the letters mean on a geologic map.
Arizona Geologic Map
Geologic map of Arizona, part of a set of all 50 states. Page 3.
Arkansas Geologic Map
Geologic map of Arkansas, part of a set of all 50 states. Page 4.
Bauxite
Bauxite is an uncommon but economically important sedimentary rock. Page 5.
Plate Tectonics Explains How the Earth's...
Start here to learn the basics of plate tectonics.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
Pennsylvania Geologic Map
Geologic map of Pennsylvania, part of a set of all 50 states. Page 38.
About Transforms - Plate Tectonic Transform...
Basics of plate tectonics: what happens when plates move past each other.
New York Geologic Map
Geologic map of New York, part of a set of all 50 states. Page 32.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
Huge Trove of Science Released to the Public
The American Geophysical Union is the world's largest publisher of Earth science research--and space science too. As an AGU member of long standing, I've
Agate
Agate is a rock made of chalcedony or cryptocrystalline quartz. Page 14.
QAP Diagram for Plutonic Rocks
QAP ternary diagram showing IUGS classification of phaneritic igneous rocks.
Is This Your Hat?
During my 2006 trip through the Sierra Nevada (at Stop 12 of the Subduction Tour, to be precise), I came upon a floppy water-resistant field hat lying on a
Oklahoma Geologic Map
Geologic map of Oklahoma, part of a set of all 50 states. Page 36.
Michigan Geologic Map
Geologic map of Michigan, part of a set of all 50 states. Page 22.
What You Should Know about the Earth's Core
The whole Earth on average consists of the same mixture of stuff we see elsewhere in the solar system, but the core has to be iron metal along with some nickel.
South Dakota Geologic Map
Geologic map of South Dakota, part of a set of all 50 states. Page 41.
1 April 2014 Chile Earthquake Completes the Set
Yesterday's magnitude 8.2 earthquake off the coast of northern Chile was significant to scientists because it was widely anticipated and because it filled the
Ohio Tightens Fracking Regulations
class="no-js" itemscope itemtype="http://schema.org/Article" > itemprop="description" >Hydraulic fracturing
Fish
Fossil fish from Eocene lake beds. Page 12.
The Promise of Geothermal Energy
Geothermal energy exploits the Earth's natural heat budget.
Ohio Geologic Map
Geologic map of Ohio, part of a set of all 50 states. Page 35.

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