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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.
Use This Master Index of Rock Pictures
My master alphabetical guide to igneous, sedimentary and metamorphic rock pictures.
What Is Chemical Weathering?
A short explanation of chemical weathering.
What to Know About Igneous Rocks
Introducing igneous rocks, first of the three great rock classes (along with sedimentary and metamorphic rocks).
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).
The Most Common Green Minerals in Nature
A guide to the most common and significant green and greenish 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
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.
10 Steps to Help You Identify Any Mineral
A mineral's luster is essential for identifying it.
Why Granite is the Signature Rock of Earth
Granite is the signature rock of the continents. Here are the basics of this important stone.
Schist
Schist is a major metamorphic rock type from regional metamorphism. Page 15.
Gneiss
Gneiss is a major metamorphic rock type from regional metamorphism. Page 6.
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.
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
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.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Quartzite
Quartzite is a major metamorphic rock type from regional metamorphism. Page 14.
Serpentinite
Serpentinite is a major metamorphic rock type from regional metamorphism. Page 16.
What Is My Blue or Purple Mineral?
A guide to the most common and significant blue and purple minerals.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
Granite
Granite is one of the major igneous rock types. Page 8.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
Basalt
Basalt is one of the major igneous rock types. Page 3.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
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.
Scoria
Scoria is one of the major igneous rock types. Page 22.
More Than 50 Different Landforms in Pictures
Find and see geological landforms at About.com Geology.
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
Obsidian
Obsidian is one of the major igneous rock types. Page 13.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
What a Black Mineral Is Most Likely to Be
A guide to the most common and significant black minerals.
How to Look at a Rock Like a Geologist
Notes on the most basic operation in geology.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
Where to Look for Rocks and Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
Sedimentary Rock Types
The major types of sedimentary rocks.
Felsite
Felsite is one of the major igneous rock types. Page 6.
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.
Syenite
Syenite is one of the major igneous rock types. Page 23.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar. Page 24.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Exfoliation
How big rock domes peel off in shells. Page 6.
Andesite
Andesite is one of the major igneous rock types.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
Coquina
Coquina is one of the major types of sedimentary rocks. Page 11.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism. Page 8.
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.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism. Page 11.
How to Use the Mohs Hardness Scale to Identify...
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks. Page 20.
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks. Page 15.
Index Fossils: The Key to Telling Deep Time
The concept of index fossils is the very basis of geologic dating.
Where Are the Greatest Earthquake Threats in...
The United Nations' global map of seismic hazard
Limestone
Limestone is one of the major types of sedimentary rocks. Page 17.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
Tuff
Tuff is one of the major igneous rock types. Page 26.
Mechanical Weathering
A short explanation of mechanical weathering.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks. Page 10.
Rock Salt
Rock salt is one of the major types of sedimentary rocks. Page 21.
The Scientific Definition of a Mineral
Minerals meet four criteria, more or less strict.
Claystone
Claystone is a type of sedimentary rock. Page 8.
Peat
Peat is one of the major types of sedimentary rocks. Page 18.
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.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism. Page 12.
Dolomite Rock or Dolostone
Dolomite or dolostone is one of the major types of sedimentary rocks. Page 14.
Coal
Coal is one of the major types of sedimentary rocks. Page 9.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
Plutonic Rocks
Plutonic rocks defined and explained.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
Diamictite
Diamictite is a messy rock that is not quite conglomerate. Page 12.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
Translate Names Between Gemstones and Minerals
Big list of mineral names and their corresponding gemstone names.
Porcellanite
Porcellanite is a subtle sedimentary rock type. Page 19.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks. Page 3.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Georgia Geologic Map
Geologic map of Georgia, part of a set of all 50 states. Page 10.
The Rise and Fall of Land Bridges
Giant causeways that link distant continents were handy ways around continental drift, but now they're mostly out of favor--mostly.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Silica Tetrahedron Defined and Explained
The silica tetrahedron is the basis of the silicate minerals.
California Geologic Map
Geologic map of California, part of a set of all 50 states. Page 5.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Argillite
A lightly metamorphosed claystone also called pipestone. Page 2.
Sizes of Tectonic or Lithospheric Plates
Table listing the lithosphere's tectonic plates by oder of size.
What to Know Before You Buy a Magnifier
What to think about and look for when you set out to get a nice magnifier.
Pyroxene (Augite)
Pyroxene is a rock-forming mineral. Page 8.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
What Is My Yellow Mineral?
A guide to the most common and significant yellow minerals.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks. Page 4.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
About Subduction in Plate Tectonics
Basics of plate tectonics: introduction to subduction.
Plate Tectonics Explains How the Earth's...
Start here to learn the basics of plate tectonics.
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.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states. Page 33.
About Transforms - Plate Tectonic Transform...
Basics of plate tectonics: what happens when plates move past each other.
Mineral Pictures A to Z
A-to-Z list of minerals shown on About.com Geology.
Olivine
Olivine is an important rock-forming mineral. Page 7.
Map of Plates and Their Boundaries
Details of the world's major tectonic plates and their boundaries.
Utah Geologic Map
Geologic map of Utah, part of a set of all 50 states. Page 44.
Tufa Towers, California
Tufa towers are a type of depositional landform. Page 18.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Gallery of Mineral Lusters
Gallery of this key attribute of minerals.
Bauxite
Bauxite is an uncommon but economically important sedimentary rock. Page 5.
Rock Cycle Diagram
The rock cycle as I see it. Geology.
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.
The Rock-Forming Minerals
A handful of very abundant minerals account for the great majority of the Earth's rocks.
Cataclasite
Cataclasite is a major metamorphic rock type from mechanical metamorphism. Page 4.
Alaska Geologic Map
Geologic map of Alaska, part of a set of all 50 states. Page 2.
Sinkhole, Oman
Sinkholes are a widespread erosional landform type. Page 23.
Actinolite
Actinolite is a major amphibole mineral. Page 5.
Feldspar (Orthoclase)
Feldspar is a major rock-forming mineral. Page 5.
Dune, California
Dunes in all their variety are depositional landforms. Page 7.
Learn to Read a Geologic Map
Understanding geologic maps starts with topography.
Coal in a Nutshell
Introducing coal: how it forms, what's in it, what it tells us.
Holes in Rocks
Geologists have named a variety of holes.
Strain
Strain, like stress, has a definite meaning in geology.
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.
Connecticut Geologic Map
Geologic map of Connecticut, part of a set of all 50 states. Page 7.
Delta, Alaska
Deltas are a type of depositional landform. Page 6.

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