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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.
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.
The Most Important Green Minerals
A guide to the most common and significant green and greenish minerals.
See the Densities of the Most Common Rock Types
Density, or specific gravity, of common rock types.
What Is My Blue or Purple Mineral?
A guide to the most common and significant blue and purple minerals.
What a Black Mineral Is Most Likely to Be
A guide to the most common and significant black minerals.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
What to Know About Sedimentary Rocks
Introducing sedimentary rocks, second of the three great rock classes (along with igneous and metamorphic rocks).
Where to Look for Rocks and Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
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.
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.
How to Look at a Rock Like a Geologist
Notes on the most basic operation in geology.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
How to Use the Mohs Hardness Scale to Identify...
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
Obsidian
Obsidian is one of the major igneous rock types. Page 13.
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
Basalt
Basalt is one of the major igneous rock types. Page 3.
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.
Quartzite
Quartzite is a major metamorphic rock type from regional metamorphism. Page 14.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Serpentinite
Serpentinite is a major metamorphic rock type from regional metamorphism. Page 16.
Granite
Granite is one of the major igneous rock types. Page 8.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
Diorite
Diorite is one of the major igneous rock types. Page 4.
Gallery of Concretions
Concretions are cemented bodies of sediment that tend to erode free.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
Andesite
Andesite is one of the major igneous rock types.
What Is Chemical Weathering?
A short explanation of chemical weathering.
What to Know Before You Buy a Magnifier
What to think about and look for when you set out to get a nice magnifier.
Sedimentary Rock Types
The major types of sedimentary rocks.
Felsite
Felsite is one of the major igneous rock types. Page 6.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
Pumice
Pumice is one of the major igneous rock types. Page 18.
Fossil Parks for Hands-On Digging
Public parks in the United States where you can collect fossils legally.
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.
Where Are the Greatest Earthquake Threats in...
The United Nations' global map of seismic hazard
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
Scoria
Scoria is one of the major igneous rock types. Page 22.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
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.
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.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
Sandstone
Sandstone is one of the major types of sedimentary rocks. Page 22.
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.
Syenite
Syenite is one of the major igneous rock types. Page 23.
The Rock-Forming Minerals
A handful of very abundant minerals account for the great majority of the Earth's rocks.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks. Page 15.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism. Page 8.
Translate Names Between Gemstones and Minerals
Big list of mineral names and their corresponding gemstone names.
Exfoliation
How big rock domes peel off in shells. Page 6.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
More Than 50 Different Landforms in Pictures
Find and see geological landforms at About.com Geology.
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
Siltstone
Siltstone is one of the major types of sedimentary rocks. Page 24.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar. Page 24.
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
Quartz and Silica Minerals Gallery
Get familiar with quartz.
Holes in Rocks
Geologists have named a variety of holes.
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.
Dolomite Rock or Dolostone
Dolomite or dolostone is one of the major types of sedimentary rocks. Page 14.
Coquina
Coquina is one of the major types of sedimentary rocks. Page 11.
The Scientific Definition of a Mineral
Minerals meet four criteria, more or less strict.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism. Page 12.
Argillite
A lightly metamorphosed claystone also called pipestone. Page 2.
Expanding Earth Animation Really Shows Plate...
The familiar expanding-Earth animation is an optical illusion based on a conceptual illusion.
Where the Top Geology Professors Get Their PhD's
These 25 American colleges grant the huge majority of the geology PhD's held by U.S. college faculty.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
Mineral Pictures A to Z
A-to-Z list of minerals shown on About.com Geology.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks. Page 10.
The Promise of Geothermal Energy
Geothermal energy exploits the Earth's natural heat budget.
Top 10 Gemstone Special Effects
The most important optical effects in gemstones, from fire to asterism.
Fast Links for Real-Time Info on Current...
Directions to information and data from earthquakes as fast as possible.
Tuff
Tuff is one of the major igneous rock types. Page 26.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
How Cement and Concrete Are Made
Cement is an artificial stone--or maybe lava.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks. Page 20.
What Is My Yellow Mineral?
A guide to the most common and significant yellow minerals.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Claystone
Claystone is a type of sedimentary rock. Page 8.
Calderas - World's Largest Calderas
Table of the world's largest known calderas: chinati mountains kari kari supervolcanoes awasa taupo new zealand
Learn to Read a Geologic Map
Understanding geologic maps starts with topography.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
Anorthosite
Anorthosite is one of the major igneous rock types. Page 2.
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.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
Plate Tectonics Explains How the Earth's...
Start here to learn the basics of plate tectonics.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
Washington Geologic Map
Geologic map of Washington, part of a set of all 50 states. Page 47.
The Bowen Reaction Series
About this staple of igneous petrology.
Rock Hammers
Hammers that geologists and rockhounds use
Mechanical Weathering
A short explanation of mechanical weathering.
Obsidian Gallery
Obsidian is an extreme variety of igneous rock with a glassy texture.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Sizes of Tectonic or Lithospheric Plates
Table listing the lithosphere's tectonic plates by oder of size.
About Chert
This interesting sedimentary rock has a key role in the geochemical cycle.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Agate
Agate is a rock made of chalcedony or cryptocrystalline quartz. Page 14.
Georgia Geologic Map
Geologic map of Georgia, part of a set of all 50 states. Page 10.
The Official State Gemstones, In One List
Thirty-five states have official gemstones. Here they are, listed by state.
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Plutonic Rocks
Plutonic rocks defined and explained.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
Coal
Coal is one of the major types of sedimentary rocks. Page 9.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states. Page 33.
Soil Classification Diagram
Triangular diagram to classify soils by their sand, silt and clay content.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Gallery of Mineral Lusters
Gallery of this key attribute of minerals.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
Michigan Geologic Map
Geologic map of Michigan, part of a set of all 50 states. Page 22.
How to Tell Apart the Granitoid Rocks
How geologists sort out granite from the rocks that look like it.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Basalt Picture Gallery
A selection of annotated photos of basalt.
Weathering: Details of This Central Geologic...
A short description of weathering.
Rock Salt
Rock salt is one of the major types of sedimentary rocks. Page 21.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
Photo Gallery of Granites
Photos of various granites and granitic rocks
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.
Olivine
Olivine is an important rock-forming mineral. Page 7.
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.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
The Great Cascadia Earthquake of 2xxx
Cascadia is America's tectonic version of Sumatra, where the great quake of 2004 occurred.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Before You Buy a Rock Collection
Advice on what to look for in those 'candy boxes' full of little rocks.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Igneous Rock Classification Diagrams
Diagrams showing IUGS classification of phaneritic and aphanitic igneous rocks.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks. Page 4.

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