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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.
The Most Common Green Minerals in Nature
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.
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
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).
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 Is My Blue or Purple Mineral?
A guide to the most common and significant blue and purple minerals.
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.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
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
Mineral identification starts with picking a good specimen.
Schist
Schist is a major metamorphic rock type from regional metamorphism. Page 15.
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.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
What Is Chemical Weathering?
A short explanation of chemical weathering.
Diorite
Diorite is one of the major igneous rock types. Page 4.
Where to Look for Rocks and Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
What a Black Mineral Is Most Likely to Be
A guide to the most common and significant black minerals.
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 Look at a Rock Like a Geologist
Notes on the most basic operation in geology.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
Why Granite is the Signature Rock of Earth
Granite is the signature rock of the continents. Here are the basics of this important stone.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Granite
Granite is one of the major igneous rock types. Page 8.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
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.
Obsidian
Obsidian is one of the major igneous rock types. Page 13.
Exfoliation
How big rock domes peel off in shells. Page 6.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
Scoria
Scoria is one of the major igneous rock types. Page 22.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Pumice
Pumice is one of the major igneous rock types. Page 18.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
Index Fossils: The Key to Telling Deep Time
The concept of index fossils is the very basis of geologic dating.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
Sedimentary Rock Types
The major types of sedimentary rocks.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Basalt
Basalt is one of the major igneous rock types. Page 3.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Syenite
Syenite is one of the major igneous rock types. Page 23.
Marble
Marble is a major metamorphic rock type from regional metamorphism. Page 10.
Georgia Geologic Map
Geologic map of Georgia, part of a set of all 50 states. Page 10.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
Sandstone: What It Is and What It Tells Us
Sandstone is sand cemented together into rock.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
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.
Felsite
Felsite is one of the major igneous rock types. Page 6.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism. Page 11.
Andesite
Andesite is one of the major igneous rock types.
North Carolina Geologic Map
Geologic map of North Carolina, part of a set of all 50 states. Page 33.
Coquina
Coquina is one of the major types of sedimentary rocks. Page 11.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
Where Are the Greatest Earthquake Threats in...
The United Nations' global map of seismic hazard
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
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.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
Limestone
Limestone is one of the major types of sedimentary rocks. Page 17.
Plate Tectonics Explains How the Earth's...
Start here to learn the basics of plate tectonics.
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Claystone
Claystone is a type of sedimentary rock. Page 8.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
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.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Sandstone
Sandstone is one of the major types of sedimentary rocks. Page 22.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks. Page 20.
How Cement and Concrete Are Made
Cement is an artificial stone--or maybe lava.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
Mineral Pictures A to Z
A-to-Z list of minerals shown on About.com Geology.
Anorthosite
Anorthosite is one of the major igneous rock types. Page 2.
How to Use the Mohs Hardness Scale to Identify...
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism. Page 12.
North Dakota Geologic Map
Geologic map of North Dakota, part of a set of all 50 states. Page 34.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks. Page 10.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
The Rock-Forming Minerals
A handful of very abundant minerals account for the great majority of the Earth's rocks.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
The Scientific Definition of a Mineral
Minerals meet four criteria, more or less strict.
Bivalves
A recent fossil clam looks like bivalves from the Early Cambrian. Page 2.
California Geologic Map
Geologic map of California, part of a set of all 50 states. Page 5.
Utah Geologic Map
Geologic map of Utah, part of a set of all 50 states. Page 44.
Fast Links for Real-Time Info on Current...
Directions to information and data from earthquakes as fast as possible.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
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.
What Is My Yellow Mineral?
A guide to the most common and significant yellow minerals.
Shark Teeth
Shark teeth, fresh and fossil, from the U.S. east coast. Page 21.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
Dinosaur Eggs
Dinosaur eggs for sale at a high-end rock shop. Page 10.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
Top-Level Geologic Time Scale: Eons, Eras and...
The periods of geologic time, part of the official geologic time scale.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
Ammonoids
Miniature ammonoid fossil, emblem of the Cretaceous.
Insect in Amber
An amber earring contains an insect fossil. Page 16.
Hawaii Geologic Map
Geologic map of Hawaii, part of a set of all 50 states. Page 11.
Diamictite
Diamictite is a messy rock that is not quite conglomerate. Page 12.
Stromatolite
Stromatolite cross-sections near Saratoga Springs, New York. Page 22.
Brachiopods
A typical brachiopod fossil. Geology. Page 3.
Rock Salt
Rock salt is one of the major types of sedimentary rocks. Page 21.
Fish
Fossil fish from Eocene lake beds. Page 12.
Mechanical Weathering
A short explanation of mechanical weathering.
Michigan Geologic Map
Geologic map of Michigan, part of a set of all 50 states. Page 22.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Banded Iron Formation
Banded iron formation or BIF is one of the major types of sedimentary rocks. Page 4.
Peat
Peat is one of the major types of sedimentary rocks. Page 18.
Alaska Geologic Map
Geologic map of Alaska, part of a set of all 50 states. Page 2.
Dung Fossils
Fecal fossils are fruitful finds. Page 11.
Foraminifers
Elphidium granti is a typical foraminifer. Page 13.
Rock Cycle Diagram
The rock cycle as I see it. Geology.
About Subduction in Plate Tectonics
Basics of plate tectonics: introduction to subduction.
Mammoth
Woolly mammoth skeleton mounted in the Lindsay Wildlife Museum. Page 17.
Olivine
Olivine is an important rock-forming mineral. Page 7.
Steno Started Geology with a Few Simple...
Steno (Niels Stensen) first set forth some of the basic principles that all geologists follow.
Translate Names Between Gemstones and Minerals
Big list of mineral names and their corresponding gemstone names.
Porphyroblast Gallery
Porphyroblasts are distinctly large crystals in a metamorphic rock. Here are pictures of some of the minerals that form porphyroblasts.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks. Page 3.
Quartz and Silica Minerals Gallery
Get familiar with quartz.
Plutonic Rocks
Plutonic rocks defined and explained.
South Carolina Geologic Map
Geologic map of South Carolina, part of a set of all 50 states. Page 40.
Horse Tooth Fossil
A fossil horse tooth from Miocene rocks in South Carolina. Page 15.
Arizona Geologic Map
Geologic map of Arizona, part of a set of all 50 states. Page 3.
Cataclasite
Cataclasite is a major metamorphic rock type from mechanical metamorphism. Page 4.
Dinosaur Bone
Dinosaur bone is cut and polished as a gemstone. Page 9.
Gastropods
Tiny aquatic snail shells preserved in a southern California mudstone. Page 14.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
Bauxite
Bauxite is an uncommon but economically important sedimentary rock. Page 5.

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