Basics of Geology
By Andrew Alden, About.com Guide
- Minerals and Gemstones
- Earth Resources
- Geologic Processes
- Geologic Hazards
- Geologic Time
- Evolution and Extinction
- Parts of the Earth
- Plate Tectonics
- Geology of Other Planets
- Teaching and Learning Geology
- References for Advanced Students
- Explore Geology: Activities & Fun
Rocks are what the Earth is made of. The first thing geologists learn is how to observe, describe and classify rocks.
- How to Look at a Rock
- What Is a Rock?
- Quick Rock Identification
- Introducing Igneous Rocks
- Igneous Rock Textures
- Sedimentary Rock Basics
- Sedimentary Textures
- Sedimentary Structures
- Metamorphic Rocks in a Nutshell
- Metamorphic Rock Fabrics
- The Rock Cycle
- State Rocks of the USA
Minerals and Gemstones
Minerals are the ingredients of rocks. Just a few important minerals account for the majority of rocks and for the soil, mud and sand of the Earth's surface. Many of the most beautiful minerals are treasured as gemstones.
- What Is a Mineral?
- Identify Minerals in 10 Steps
- The Mohs Scale of Mineral Hardness
- Learn Your Minerals: An Email Course
- Index of Mineral Photos
- The 9 Common Rock-Forming Minerals
- Minerals of the Earth's Surface
- Gemstones and their Mineral Names
- Optical Effects in Gemstones
- Black Minerals
- Blue/Bluish Minerals
- Brown Minerals
- Green/Greenish Minerals
- Metallic Minerals
- Red/Pink Minerals
- Yellow/Yellowish Minerals
- State Minerals of the USA
Many rocks and minerals are important for civilization. They are products we take from the Earth. Learn more about their geology.
- Where We Get Stone & Rock Products
- Stone Tools Ancient and Modern
- Geothermal Energy
- The Seven Fossil Fuels
- Petroleum - Oil and Gas
- Coal Basics
- About Salt
- Iron and Iron Minerals
- Uranium Geology
- About Mercury
- Conflict Diamonds and Other Minerals
- Cement and Concrete
- Brick: An Artificial Rock
- Phosphate in a Nutshell
- Water and Hydrology
Geology is not just rocks and minerals, but also the things that happen to them in the great Earth cycle.
- Mechanical or Physical Weathering
- Chemical Weathering
- Organic or Biological Weathering
- Erosion Defined
- Erosion Explained
- Sedimentary Structures
- Geologic Processes Gallery
- Mass Wasting (Landsliding)
- Serpentinization, Altering the Crust
- Mountain Building (Orogenesis)
- About Magma and Lava
Hazards are ordinary geologic processes that interfere with human life. Here are introductions to the major geologic hazards. For news and background about current hazard events, see the Quakes, Volcanoes Etc tab.
The hills, valleys and other features of a landscape are signs of the area's underlying structure and clues to its history.
- Erosional Landforms
- Depositional Landforms
- Tectonic Landforms
- Glaciers and Glacial Landforms
- Dry Lake Beds and Salt Flats
All of human history is the briefest moment at the end of four billion years of geologic time. How do geologists measure and order the milestones in Earth's long history?
- Geologic Eons and Eras, the Large Scale
- Precambrian Time Scale, 4500 to 542 Million Years Ago
- Phanerozoic Time Scale, 542 Million Years Ago to Present
- How We Map Deep Time
- Paleozoic Era Time Scale (542 to 251 Million Years Ago)
- Mesozoic Era Time Scale (251 to 66 Million Years Ago)
- Cenozoic Era Time Scale (66 Million Years Ago to Present)
- How We Measure Deep Time
Fossils are precious gifts from the geologic past: signs and remains of ancient living things that help explain how life has coexisted with Earth. Fossils are an important line of evidence showing how life has evolved since its still-mysterious beginnings.
- What Are Fossils?
- Fossilized or Petrified?
- Dinosaurs and other Fossil Creatures
- Ancient Unfossilized Remains
- Lagerstätten: Universal Graveyards
- Collect Fossils
- How Fossil Species Are Defined
- Official State Fossils of the United States
Evolution and Extinction
The consistent parade of fossil species through geologic time shows that life has been evolving since its remote beginning. Modern genetics tells the same story. Geology also shows that species have gone extinct.
Parts of the Earth
Beneath the stony crust lie the rocky mantle and, at Earth's heart, the iron core. All are areas of active research and competing theories.
Plate tectonics is the first theory that explains the mechanics of the Earth's surface in depth, in detail and in a scientifically fruitful way.
Geology of Other Planets
The space program has revolutionized geology by giving us other examples of planets besides our own: they include Mercury, Venus, the Moon, Mars, the asteroids and the larger planetary satellites.
Teaching and Learning Geology
Charles Darwin once wrote, "Geology is a capital science to begin, as it requires nothing but a little reading, thinking, and hammering." Whether you study for pleasure at home or stand in a classroom and teach, I can help.
- How to Read a Geologic Map
- Do-It-Yourself Geology News
- Ten Good News Sources
- Geologic Journals Online
- Geology Webcams Around the World
- Geologic Topics in a Nutshell
- Earth Science Scales
- Teacher Resources Grades K to 4
- Teacher Resources Grades 5 to 8
- Teacher Resources Grades 9 to 12
- College Teachers' Resources
References for Advanced Students
A compendium of handy lists, tools and photo galleries. Even the experts don't keep it all in their heads.
- Identify the Rock-Forming Minerals
- Formulas of Rock-Forming Minerals
- Igneous Rock Textures
- Igneous Rock Classification Diagrams
- Sorting Out the Granitoids
- Extrusive Igneous Rock Pictures
- Sedimentary Rock Pictures
- Sedimentary Rock Classification
- Wentworth Grain Size Scale
- Metamorphic Rock Pictures
- Geologic Features & Processes
- Types of Holes in Rocks
- Poison Plants in the Field
- Geochemical Abbreviations
- Landform Pictures
- Unconformity Types
- Earthquake Focal Mechanisms
- Earthquake Intensity Scales
- Periodic Table of the Elements
Explore Geology: Activities & Fun
Go beyond the basics and start getting geology into your life.