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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.
The Most Common Green Minerals in Nature
A guide to the most common and significant green and greenish minerals.
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
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
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.
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.
Siltstone
Siltstone is one of the major types of sedimentary rocks. Page 24.
Serpentinite
Serpentinite is a major metamorphic rock type from regional metamorphism. Page 16.
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.
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.
What Is My Blue or Purple Mineral?
A guide to the most common and significant blue and purple minerals.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
What Is Chemical Weathering?
A short explanation of chemical weathering.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
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.
Why Granite is the Signature Rock of Earth
Granite is the signature rock of the continents. Here are the basics of this important stone.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Quartzite
Quartzite is a major metamorphic rock type from regional metamorphism. Page 14.
Granite
Granite is one of the major igneous rock types. Page 8.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
What a Black Mineral Is Most Likely to Be
A guide to the most common and significant black minerals.
Sedimentary Rock Types
The major types of sedimentary rocks.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
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.
Basalt
Basalt is one of the major igneous rock types. Page 3.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
Sandstone: What It Is and What It Tells Us
Sandstone is sand cemented together into rock.
Scoria
Scoria is one of the major igneous rock types. Page 22.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
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.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
Marble
Marble is a major metamorphic rock type from regional metamorphism. Page 10.
Felsite
Felsite is one of the major igneous rock types. Page 6.
Andesite
Andesite is one of the major igneous rock types.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
Anorthosite
Anorthosite is one of the major igneous rock types. Page 2.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
Sandstone
Sandstone is one of the major types of sedimentary rocks. Page 22.
9 Different Minerals That Are Used as Abrasives
A survey of 9 mineral substances whose properties make them useful abrasives.
Coquina
Coquina is one of the major types of sedimentary rocks. Page 11.
How to Look at a Rock Like a Geologist
Notes on the most basic operation in geology.
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
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
Exfoliation
How big rock domes peel off in shells. Page 6.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
Syenite
Syenite is one of the major igneous rock types. Page 23.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks. Page 20.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism. Page 8.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar. Page 24.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states. Page 33.
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
Tuff
Tuff is one of the major igneous rock types. Page 26.
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks. Page 15.
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.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Claystone
Claystone is a type of sedimentary rock. Page 8.
Fast Links for Real-Time Info on Current...
Directions to information and data from earthquakes as fast as possible.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism. Page 11.
Limestone
Limestone is one of the major types of sedimentary rocks. Page 17.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
Georgia Geologic Map
Geologic map of Georgia, part of a set of all 50 states. Page 10.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks. Page 10.
Peat
Peat is one of the major types of sedimentary rocks. Page 18.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
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.
Coal
Coal is one of the major types of sedimentary rocks. Page 9.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
Plutonic Rocks
Plutonic rocks defined and explained.
Mechanical Weathering
A short explanation of mechanical weathering.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
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.
The Scientific Definition of a Mineral
Minerals meet four criteria, more or less strict.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism. Page 12.
Mineral Pictures A to Z
A-to-Z list of minerals shown on About.com Geology.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
Porcellanite
Porcellanite is a subtle sedimentary rock type. Page 19.
Sizes of Tectonic or Lithospheric Plates
Table listing the lithosphere's tectonic plates by oder of size.
The Rock-Forming Minerals
A handful of very abundant minerals account for the great majority of the Earth's rocks.
North Dakota Geologic Map
Geologic map of North Dakota, part of a set of all 50 states. Page 34.
California Geologic Map
Geologic map of California, part of a set of all 50 states. Page 5.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks. Page 4.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks. Page 3.
Silica Tetrahedron Defined and Explained
The silica tetrahedron is the basis of the silicate minerals.
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.
More Than 50 Different Landforms in Pictures
Find and see geological landforms at About.com Geology.
Argillite
A lightly metamorphosed claystone also called pipestone. Page 2.
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.
Weathering: Details of This Central Geologic...
A short description of weathering.
Michigan Geologic Map
Geologic map of Michigan, part of a set of all 50 states. Page 22.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
Utah Geologic Map
Geologic map of Utah, part of a set of all 50 states. Page 44.
What Is My Yellow Mineral?
A guide to the most common and significant yellow minerals.
Rock Cycle Diagram
The rock cycle as I see it. Geology.
Alaska Geologic Map
Geologic map of Alaska, part of a set of all 50 states. Page 2.
Wind Abrasion
Wind can sandblast stones, even landscapes. Page 13.
Arizona Geologic Map
Geologic map of Arizona, part of a set of all 50 states. Page 3.
Sedimentary Rock Classification Diagrams
Diagrams to help classify sedimentary rocks.
Bauxite
Bauxite is an uncommon but economically important sedimentary rock. Page 5.
Cataclasite
Cataclasite is a major metamorphic rock type from mechanical metamorphism. Page 4.
About Transforms - Plate Tectonic Transform...
Basics of plate tectonics: what happens when plates move past each other.
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.
Map of Plates and Their Boundaries
Details of the world's major tectonic plates and their boundaries.
Plate Tectonics Explains How the Earth's...
Start here to learn the basics of plate tectonics.
Olivine
Olivine is an important rock-forming mineral. Page 7.
Pluton
Plutons defined and explained. Plutons are bodies of plutonic rock: deep-seated and large-grained.
QAP Diagram for Plutonic Rocks
QAP ternary diagram showing IUGS classification of phaneritic igneous rocks.
Hawaii Geologic Map
Geologic map of Hawaii, part of a set of all 50 states. Page 11.
Insect in Amber
An amber earring contains an insect fossil. Page 16.
Fossils: What They Are, How They Form, How They...
Fossils are precious gifts from the geologic past: signs and remains of ancient living things preserved in the Earth's crust.
Porphyroblast Gallery
Porphyroblasts are distinctly large crystals in a metamorphic rock. Here are pictures of some of the minerals that form porphyroblasts.
Alabaster
Alabaster or massive gypsum rock is one of the sedimentary rocks.
The Promise of Geothermal Energy
Geothermal energy exploits the Earth's natural heat budget.

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