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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.
Use This Master Index of Rock Pictures
My master alphabetical guide to igneous, sedimentary and metamorphic rock pictures.
See the Densities of the Most Common Rock Types
Density, or specific gravity, of common rock types.
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 Igneous Rocks
Introducing igneous rocks, first of the three great rock classes (along with sedimentary and metamorphic rocks).
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.
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.
The Most Common Green Minerals in Nature
A guide to the most common and significant green and greenish minerals.
10 Steps to Help You Identify Any Mineral
Cleavage, the way a mineral breaks, is crucial for identifying minerals.
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
Why Granite is the Signature Rock of Earth
Granite is the signature rock of the continents. Here are the basics of this important stone.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
What Is Chemical Weathering?
A short explanation of chemical weathering.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
More Than 50 Different Landforms in Pictures
Find and see geological landforms at About.com Geology.
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.
How to Look at a Rock Like a Geologist
Notes on the most basic operation in geology.
What Is My Blue or Purple Mineral?
A guide to the most common and significant blue and purple minerals.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Granite
Granite is one of the major igneous rock types. Page 8.
Schist
Schist is a major metamorphic rock type from regional metamorphism. Page 15.
Diorite
Diorite is one of the major igneous rock types. Page 4.
Basalt
Basalt is one of the major igneous rock types. Page 3.
Where to Look for Rocks and Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
Obsidian
Obsidian is one of the major igneous rock types. Page 13.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
Pumice
Pumice is one of the major igneous rock types. Page 18.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
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.
Gneiss
Gneiss is a major metamorphic rock type from regional metamorphism. Page 6.
How to Use the Mohs Hardness Scale to Identify...
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
What a Black Mineral Is Most Likely to Be
A guide to the most common and significant black minerals.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
Scoria
Scoria is one of the major igneous rock types. Page 22.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
What You Should Know About the San Andreas Fault
Home page for everything about the San Andreas fault: where it is, how it behaves, what it means.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
Exfoliation
How big rock domes peel off in shells. Page 6.
Siltstone
Siltstone is one of the major types of sedimentary rocks. Page 24.
Felsite
Felsite is one of the major igneous rock types. Page 6.
Sedimentary Rock Types
The major types of sedimentary rocks.
Syenite
Syenite is one of the major igneous rock types. Page 23.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar. Page 24.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
Andesite
Andesite is one of the major igneous rock types.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Sandstone: What It Is and What It Tells Us
Sandstone is sand cemented together into rock.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Tuff
Tuff is one of the major igneous rock types. Page 26.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
Anorthosite
Anorthosite is one of the major igneous rock types. Page 2.
Sandstone
Sandstone is one of the major types of sedimentary rocks. Page 22.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Sizes of Tectonic or Lithospheric Plates
Table listing the lithosphere's tectonic plates by oder of size.
Mechanical Weathering
A short explanation of mechanical weathering.
Marble
Marble is a major metamorphic rock type from regional metamorphism. Page 10.
Limestone
Limestone is one of the major types of sedimentary rocks. Page 17.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism. Page 8.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
The Scientific Definition of a Mineral
Minerals meet four criteria, more or less strict.
Where Are the Greatest Earthquake Threats in...
The United Nations' global map of seismic hazard
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks. Page 15.
About Transforms - Plate Tectonic Transform...
Basics of plate tectonics: what happens when plates move past each other.
Silica Tetrahedron Defined and Explained
The silica tetrahedron is the basis of the silicate minerals.
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.
Utah Geologic Map
Geologic map of Utah, part of a set of all 50 states. Page 44.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Translate Names Between Gemstones and Minerals
Big list of mineral names and their corresponding gemstone names.
What Is My Yellow Mineral?
A guide to the most common and significant yellow minerals.
About Subduction in Plate Tectonics
Basics of plate tectonics: introduction to subduction.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
The Bowen Reaction Series
About this staple of igneous petrology.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism. Page 11.
Coquina
Coquina is one of the major types of sedimentary rocks. Page 11.
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
What to Know Before You Buy a Magnifier
What to think about and look for when you set out to get a nice magnifier.
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.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
California Geologic Map
Geologic map of California, part of a set of all 50 states. Page 5.
Index Fossils: The Key to Telling Deep Time
The concept of index fossils is the very basis of geologic dating.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks. Page 20.
Mineral Pictures A to Z
A-to-Z list of minerals shown on About.com Geology.
Argillite
A lightly metamorphosed claystone also called pipestone. Page 2.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
About Convergent Zones in Plate Tectonics
Basics of plate tectonics: convergent zones are where plates come together.
About Divergent Zones in Plate Tectonics
Basics of plate tectonics: divergent zones are where plates move apart.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
Claystone
Claystone is a type of sedimentary rock. Page 8.
Map of Plates and Their Boundaries
Details of the world's major tectonic plates and their boundaries.
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.
Coal
Coal is one of the major types of sedimentary rocks. Page 9.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
Peat
Peat is one of the major types of sedimentary rocks. Page 18.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states. Page 33.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
Mineral Habits
The various forms that minerals take in rocks.
Georgia Geologic Map
Geologic map of Georgia, part of a set of all 50 states. Page 10.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Rock Salt
Rock salt is one of the major types of sedimentary rocks. Page 21.
Dolomite Rock or Dolostone
Dolomite or dolostone is one of the major types of sedimentary rocks. Page 14.
Weathering: Details of This Central Geologic...
A short description of weathering.
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
Plutonic Rocks
Plutonic rocks defined and explained.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks. Page 4.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks. Page 3.
The Rock-Forming Minerals
A handful of very abundant minerals account for the great majority of the Earth's rocks.
Learn to Read a Geologic Map
Understanding geologic maps starts with topography.
Diamictite
Diamictite is a messy rock that is not quite conglomerate. Page 12.
Top-Level Geologic Time Scale: Eons, Eras and...
The periods of geologic time, part of the official geologic time scale.
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
Olivine
Olivine is an important rock-forming mineral. Page 7.
Rock Cycle Diagram
The rock cycle as I see it. Geology.
How Earth Was Born: The Quick Story
The straight story of how Earth began, as today's geologists tell it.
Porcellanite
Porcellanite is a subtle sedimentary rock type. Page 19.
Vermont Geologic Map
Geologic map of Vermont, part of a set of all 50 states. Page 45.
Fossil Parks for Hands-On Digging
Public parks in the United States where you can collect fossils legally.
Pyroxene (Augite)
Pyroxene is a rock-forming mineral. Page 8.
Gallery of Mineral Lusters
Gallery of this key attribute of minerals.
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.
Expanding Earth Animation Really Shows Plate...
The familiar expanding-Earth animation is an optical illusion based on a conceptual illusion.
Erosion: Introduction to This Central Concept...
A short explanation of erosion. Geology.
Delta, Alaska
Deltas are a type of depositional landform. Page 6.
Fast Links for Real-Time Info on Current...
Directions to information and data from earthquakes as fast as possible.

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