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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.
Why the Earth's Crust Is So Important
The Earth's crust is exceptionally important, and not just because we live on it.
What Is Chemical Weathering?
A short explanation of chemical weathering.
Use This Master Index of Rock Pictures
My master alphabetical guide to igneous, sedimentary and metamorphic rock pictures.
What to Know About Igneous Rocks
Introducing igneous rocks, first of the three great rock classes (along with sedimentary and metamorphic rocks).
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
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 Common Green Minerals in Nature
A guide to the most common and significant green and greenish minerals.
10 Steps to Help You Identify Any Mineral
Mineral identification starts with picking a good specimen.
Quartzite
Quartzite is a major metamorphic rock type from regional metamorphism. Page 14.
Schist
Schist is a major metamorphic rock type from regional metamorphism. Page 15.
Gabbro
Gabbro is one of the major igneous rock types. Page 7.
Slate
Slate is a major metamorphic rock type from regional metamorphism. Page 17.
Why Granite is the Signature Rock of Earth
Granite is the signature rock of the continents. Here are the basics of this important stone.
Gneiss
Gneiss is a major metamorphic rock type from regional metamorphism. Page 6.
Serpentinite
Serpentinite is a major metamorphic rock type from regional metamorphism. Page 16.
Siltstone
Siltstone is one of the major types of sedimentary rocks. Page 24.
Metamorphic Rock Types
The major metamorphic rock types, from regional, contact and mechanical metamorphism.
Diorite
Diorite is one of the major igneous rock types. Page 4.
Granite
Granite is one of the major igneous rock types. Page 8.
What Is My Blue or Purple Mineral?
A guide to the most common and significant blue and purple minerals.
Fault Types in a Nutshell
The three basic types of fault, with their nomenclature, in a nutshell.
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.
Where to Look for Rocks and Minerals
Rocks and minerals can be found everywhere, but there is a learning process involved.
Igneous Rock Types
The major igneous rock types, plutonic, intrusive and extrusive.
Basalt
Basalt is one of the major igneous rock types. Page 3.
How to Tell the Feldspar Minerals Apart
Feldspar is the commonest mineral in the Earth's crust, but identifying it can be tricky.
Pegmatite
Pegmatite is one of the major igneous rock types. Page 14.
Phyllite
Phyllite is a major metamorphic rock type from regional metamorphism. Page 13.
Pumice
Pumice is one of the major igneous rock types. Page 18.
Peridotite
Peridotite is one of the major igneous rock types. Page 15.
Sedimentary Rock Types
The major types of sedimentary rocks.
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.
Viewing Earth from on High
Satellite views of Earth's surface make possible geological discoveries never before imagined.
Granodiorite
Granodiorite is one of the major igneous rock types. Page 9.
More Than 50 Different Landforms in Pictures
Find and see geological landforms at About.com Geology.
Scoria
Scoria is one of the major igneous rock types. Page 22.
Exfoliation
How big rock domes peel off in shells. Page 6.
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.
Porphyry
Porphyry is one of the major igneous rock types. Page 17.
Pyroxenite
Pyroxenite is one of the major igneous rock types. Page 19.
Syenite
Syenite is one of the major igneous rock types. Page 23.
Dunite
Dunite is a plutonic rock consisting of olivine. Page 5.
Rhyolite
Rhyolite is one of the major igneous rock types. Page 21.
Marble
Marble is a major metamorphic rock type from regional metamorphism. Page 10.
Mechanical Weathering
A short explanation of mechanical weathering.
Komatiite
Komatiite is a rare and ancient ultramafic lava. Page 11.
Andesite
Andesite is one of the major igneous rock types.
Quartz Monzonite
Quartz monzonite is one of the major igneous rock types. Page 20.
Perlite
Perlite is one of the major igneous rock types. Page 16.
Tonalite
Tonalite is a felsic plutonic rock without alkali feldspar. Page 24.
Greenstone
Grenstone is a major metamorphic rock type from regional metamorphism. Page 8.
How to Use the Mohs Hardness Scale to Identify...
The 10-mineral Mohs scale of relative hardness is based on what scratches what.
Shale
Shale is one of the major types of sedimentary rocks. Page 23.
Fossil Picture Gallery
Pictures of fossils, part of the About.com Geology gallery of images.
Quartz: How to Tell It, Different Kinds, What...
Quartz is essential to the land as we know it.
Migmatite
Migmatite is a major metamorphic rock type from regional metamorphism. Page 11.
Sandstone
Sandstone is one of the major types of sedimentary rocks. Page 22.
Kimberlite
Kimberlite is the peculiar deep-seated ultramafic rock most famous as the ore of diamonds. Page 10.
Chert
Chert is one of the major types of sedimentary rocks. Page 7.
Latite
Latite is the extrusive equivalent of monzonite. Page 12.
Troctolite
Troctolite is one of the gabbroid rocks: igneous, plutonic and mafic. Page 25.
Graywacke or Wacke
Wacke or graywacke is one of the major types of sedimentary rocks. Page 15.
Greenschist
Greenschist is a major metamorphic rock type from regional metamorphism. Page 7.
Arkose
Arkose is one of the major types of sedimentary rocks. Page 2.
Anorthosite
Anorthosite is one of the major igneous rock types. Page 2.
What Is My Red or Pink Mineral?
A guide to the most common and significant red and pink minerals.
Tuff
Tuff is one of the major igneous rock types. Page 26.
Rock Gypsum
Rock gypsum is one of the major types of sedimentary rocks. Page 20.
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.
Hornfels
Hornfels is a major metamorphic rock type from contact metamorphism. Page 9.
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.
Travertine
Travertine is one of the major types of sedimentary rocks. Page 25.
Mylonite
Mylonite is a major metamorphic rock type from mechanical metamorphism. Page 12.
Soapstone
Soapstone is a major metamorphic rock type from regional metamorphism. Page 18.
Dolomite Rock or Dolostone
Dolomite or dolostone is one of the major types of sedimentary rocks. Page 14.
Limestone
Limestone is one of the major types of sedimentary rocks. Page 17.
Conglomerate
Conglomerate is one of the major types of sedimentary rocks. Page 10.
Volcanic (Extrusive) Rock Types
Photos of the types of erupted igneous rocks.
Where Are the Greatest Earthquake Threats in...
The United Nations' global map of seismic hazard
Rock Salt
Rock salt is one of the major types of sedimentary rocks. Page 21.
Blueschist
Blueschist is a major metamorphic rock type from regional metamorphism. Page 3.
Diatomite
Picture and notes about the sedimentary rock diatomite. Page 13.
Ironstone
Several types of sedimentary rocks are called ironstone. Page 16.
Minerals with Metallic Luster
Minerals with metallic luster are easy to learn to identify.
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.
Breccia
Breccia is one of the major types of sedimentary rocks. Page 6.
Claystone
Claystone is a type of sedimentary rock. Page 8.
Plutonic Rocks
Plutonic rocks defined and explained.
Index Fossils: The Key to Telling Deep Time
The concept of index fossils is the very basis of geologic dating.
Diamictite
Diamictite is a messy rock that is not quite conglomerate. Page 12.
Coal
Coal is one of the major types of sedimentary rocks. Page 9.
The Lithosphere in a Nutshell
What you need to know about the lithosphere.
Translate Names Between Gemstones and Minerals
Big list of mineral names and their corresponding gemstone names.
Coral (Solitary or Rugose)
Rugose or solitary corals were abundant in the Paleozoic Era but are now extinct. Page 7.
Peat
Peat is one of the major types of sedimentary rocks. Page 18.
Measuring Plate Motion
The five ways we track the motion of the lithospheric plates.
What Counts as a Rock to a Geologist?
Everyone knows what a rock is, until you ask what it is exactly.
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.
Quartz
Quartz is classified as a rock-forming mineral. Page 9.
Eclogite
Eclogite is a major metamorphic rock type from regional metamorphism. Page 5.
Texas Geologic Map
Geologic map of Texas, part of a set of all 50 states. Page 43.
Rock Cycle Diagram
The rock cycle as I see it. Geology.
Colorado Geologic Map
Geologic map of Colorado, part of a set of all 50 states. Page 6.
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.
Argillite
A lightly metamorphosed claystone also called pipestone. Page 2.
The Bowen Reaction Series
About this staple of igneous petrology.
Mineral Pictures A to Z
A-to-Z list of minerals shown on About.com Geology.
Natural Asphalt
Natural asphalt is one of the major types of sedimentary rocks. Page 3.
Porcellanite
Porcellanite is a subtle sedimentary rock type. Page 19.
Brachiopods
A typical brachiopod fossil. Geology. Page 3.
Coral (Colonial)
Colonial coral fossils are found in most Phanerozoic rocks. Page 6.
Crinoids
Crinoid stems are especially common in late Paleozoic rocks. Page 8.
Amphibolite
Amphibolite is one of the major metamorphic rock types.
Calcite
Calcite is one of the carbonate minerals. Page 2.
About Subduction in Plate Tectonics
Basics of plate tectonics: introduction to subduction.
What to Know Before You Buy a Magnifier
What to think about and look for when you set out to get a nice magnifier.
Frost Heave
Freezing ground ice lifts and shifts sediment. Page 7.
Geologic Maps of the 50 United States
Geologic maps of all 50 U.S. states.
Sizes of Tectonic or Lithospheric Plates
Table listing the lithosphere's tectonic plates by oder of size.
Cataclasite
Cataclasite is a major metamorphic rock type from mechanical metamorphism. Page 4.
Bauxite
Bauxite is an uncommon but economically important sedimentary rock. Page 5.
Erosion: Introduction to This Central Concept...
A short explanation of erosion. Geology.
The Official State Gemstones, In One List
Thirty-five states have official gemstones. Here they are, listed by state.
Fast Links for Real-Time Info on Current...
Directions to information and data from earthquakes as fast as possible.
Florida Geologic Map
Geologic map of Florida, part of a set of all 50 states. Page 9.
Bivalves
A recent fossil clam looks like bivalves from the Early Cambrian. Page 2.
Insect in Amber
An amber earring contains an insect fossil. Page 16.
Lithification
Lithification is how sediments are turned to rock.
How Volcanoes Caused the Great Dying: The...
The greatest mass extinction of the last 500 million years or Phanerozoic Eon happened 250 million years ago, ending the Permian Period and beginning the Triassic Period.
Actinolite
Actinolite is a major amphibole mineral. Page 5.
Olivine
Olivine is an important rock-forming mineral. Page 7.
Potassium-Argon Dating Methods
Potassium-argon isotopic dating is especially useful for determining the age of lavas.
Pyroxene (Augite)
Pyroxene is a rock-forming mineral. Page 8.
Trilobite
Trilobite fossil from Arizona. Geology. Page 23.
What Is an Ophiolite?
Not a rock type, it's a whole assemblage of crustal rocks.
Iowa Geologic Map
Geologic map of Iowa, part of a set of all 50 states. Page 15.
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.
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.
Foraminifers
Elphidium granti is a typical foraminifer. Page 13.

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