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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.
The Most Common Green Minerals in Nature
A guide to the most common and significant green and greenish minerals.
Where Are the Greatest Earthquake Threats in...
The United Nations' global map of seismic hazard
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.
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).
Fast Links for Real-Time Info on Current...
Directions to information and data from earthquakes as fast as possible.
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).
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
What Is Chemical Weathering?
A short explanation of chemical weathering.
10 Steps to Help You Identify Any Mineral
Mineral identification starts with picking a good specimen.
Why the Earth's Crust Is So Important
The Earth's crust is exceptionally important, and not just because we live on it.
Index Fossils: The Key to Telling Deep Time
The concept of index fossils is the very basis of geologic dating.
How to Look at a Rock Like a Geologist
Notes on the most basic operation in geology.
Serpentinite
Serpentinite is a major metamorphic rock type from regional metamorphism. Page 16.
Where to Look for Rocks and Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
Siltstone
Siltstone is one of the major types of sedimentary rocks. Page 24.
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.
Granite
Granite is one of the major igneous rock types. Page 8.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
Diorite
Diorite is one of the major igneous rock types. Page 4.
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
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.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Pumice
Pumice is one of the major igneous rock types. Page 18.
Scoria
Scoria is one of the major igneous rock types. Page 22.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
Basalt
Basalt is one of the major igneous rock types. Page 3.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
Obsidian
Obsidian is one of the major igneous rock types. Page 13.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Syenite
Syenite is one of the major igneous rock types. Page 23.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar. Page 24.
Quartzite
Quartzite is a major metamorphic rock type from regional metamorphism. Page 14.
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.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Why Granite is the Signature Rock of Earth
Granite is the signature rock of the continents. Here are the basics of this important stone.
Exfoliation
How big rock domes peel off in shells. Page 6.
Felsite
Felsite is one of the major igneous rock types. Page 6.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
Sedimentary Rock Types
The major types of sedimentary rocks.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
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.
Sandstone: What It Is and What It Tells Us
Sandstone is sand cemented together into rock.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Tuff
Tuff is one of the major igneous rock types. Page 26.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism. Page 8.
Andesite
Andesite is one of the major igneous rock types.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Mechanical Weathering
A short explanation of mechanical weathering.
Marble
Marble is a major metamorphic rock type from regional metamorphism. Page 10.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks. Page 15.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
Coquina
Coquina is one of the major types of sedimentary rocks. Page 11.
Limestone
Limestone is one of the major types of sedimentary rocks. Page 17.
Sandstone
Sandstone is one of the major types of sedimentary rocks. Page 22.
California Geologic Map
Geologic map of California, part of a set of all 50 states. Page 5.
Claystone
Claystone is a type of sedimentary rock. Page 8.
What Is My Yellow Mineral?
A guide to the most common and significant yellow minerals.
Georgia Geologic Map
Geologic map of Georgia, part of a set of all 50 states. Page 10.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
Anorthosite
Anorthosite is one of the major igneous rock types. Page 2.
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.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states. Page 33.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks. Page 10.
Michigan Geologic Map
Geologic map of Michigan, part of a set of all 50 states. Page 22.
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.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism. Page 11.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
Diamictite
Diamictite is a messy rock that is not quite conglomerate. Page 12.
Dolomite Rock or Dolostone
Dolomite or dolostone is one of the major types of sedimentary rocks. Page 14.
Sizes of Tectonic or Lithospheric Plates
Table listing the lithosphere's tectonic plates by oder of size.
Peat
Peat is one of the major types of sedimentary rocks. Page 18.
Top 10 Action Steps to Take Against Earthquakes
Earthquake professionals list the elements of a quake-resistant society.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
Coal
Coal is one of the major types of sedimentary rocks. Page 9.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Rock Salt
Rock salt is one of the major types of sedimentary rocks. Page 21.
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.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks. Page 4.
Connecticut Geologic Map
Geologic map of Connecticut, part of a set of all 50 states. Page 7.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
The Rock-Forming Minerals
A handful of very abundant minerals account for the great majority of the Earth's rocks.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism. 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.
Dinosaur Eggs
Dinosaur eggs for sale at a high-end rock shop. Page 10.
Translate Names Between Gemstones and Minerals
Big list of mineral names and their corresponding gemstone names.
Minnesota Geologic Map
Geologic map of Minnesota, part of a set of all 50 states. Page 23.
Quartz and Silica Minerals Gallery
Get familiar with quartz.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks. Page 3.
Holes in Rocks
Geologists have named a variety of holes.
Weathering: Details of This Central Geologic...
A short description of weathering.
Brown Minerals
A guide to the most common and significant brown minerals.
More Than 50 Different Landforms in Pictures
Find and see geological landforms at About.com Geology.
Actinolite
Actinolite is a major amphibole mineral. Page 5.
Shark Teeth
Shark teeth, fresh and fossil, from the U.S. east coast. Page 21.
Rock Cycle Diagram
The rock cycle as I see it. Geology.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
Porcellanite
Porcellanite is a subtle sedimentary rock type. Page 19.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
North Dakota Geologic Map
Geologic map of North Dakota, part of a set of all 50 states. Page 34.
Calderas - World's Largest Calderas
Table of the world's largest known calderas: chinati mountains kari kari supervolcanoes awasa taupo new zealand
Utah Geologic Map
Geologic map of Utah, part of a set of all 50 states. Page 44.
Sedimentary Rock Classification Diagrams
Diagrams to help classify sedimentary rocks.
Insect in Amber
An amber earring contains an insect fossil. Page 16.
Bauxite
Bauxite is an uncommon but economically important sedimentary rock. Page 5.
Arizona Geologic Map
Geologic map of Arizona, part of a set of all 50 states. Page 3.
About Subduction in Plate Tectonics
Basics of plate tectonics: introduction to subduction.
Metamorphic Rock Gallery
A spectrum of metamorphic rocks, the pelitic sequence and the basaltic sequence.
What to Know Before You Buy a Magnifier
What to think about and look for when you set out to get a nice magnifier.
Argillite
A lightly metamorphosed claystone also called pipestone. Page 2.
The Official State Gemstones, In One List
Thirty-five states have official gemstones. Here they are, listed by state.
Hawaii Geologic Map
Geologic map of Hawaii, part of a set of all 50 states. Page 11.
How to Tell Apart the Granitoid Rocks
How geologists sort out granite from the rocks that look like it.
Petrified Wood and Fossil Trees
Fossil wood, or petrified wood. Geology. Page 19.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Stromatolite
Stromatolite cross-sections near Saratoga Springs, New York. Page 22.
South Dakota Geologic Map
Geologic map of South Dakota, part of a set of all 50 states. Page 41.
The Scientific Definition of a Mineral
Minerals meet four criteria, more or less strict.
Plate Tectonics Explains How the Earth's...
Start here to learn the basics of plate tectonics.

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