At one time or another, you have probably held a rock in your hand. Recall the texture. Was it smooth, polished by the force of sand and salt water pounding it onto the beach? Was it rough and cragged, left exposed for centuries to the wind and sun of a canyon wall? Recall the color. Was it coral and pink, like the colors of Bermuda's sand? Was it fiery red, like the colors of Arizona's canyons? Recall the size. Was it a handful, heavy with the weight of being worn? Was it a tiny pebble, a small fragment broken off from what it once was?

Rock is our world. The planet Earth is, essentially, just one big interesting rock, sometimes called "the third rock from the sun." The multi-faceted rock we live on supports life in many ways. The deep oceans, the vast deserts, and the high mountains, are just a few of the ways rock emerges and supports life.

Rock remembers. Geology is the science and study of the earth and its life, especially as recorded in rock. Rock, then, keeps record of the passage of time and the evolution of living things.

The word rock refers to solid mineral deposits. Rock is mineral, but not all minerals are rock. Minerals are all substances that can't be classified as "animal" or "vegetable." Metal ores found in the earth, like gold and silver, are minerals. Crystalline substances, like salt and quartz, are minerals. Homogeneous natural substances, like water and gas, are also minerals. These non-solid minerals, however, are not considered "rock."

Begin with Minerals
Minerals are classified in several "classes" based upon common properties or characteristics. Explore the diversity of minerals as preparation for thinking about rock. The alphabetical listing of minerals by name quickly shows how diverse minerals really are. Specimens, on display at The Geology Museum, range from the most common to the extremely rare. The Mineral Gallery offers both descriptions and a growing collection of images.

The Mineral Gallery

Minerals By Name

Minerals from the Geology Museum

The Clausthal Online Mineral Collection

The Mineral and Gemstone Kingdom

Alphabetical Mineral Reference

Chemical Formulae for Minerals and Gems

Commercial Mineral Names

A Virtual Tour of the Janet Annenberg Hooker Hall of Geology, Gems, and Minerals at the Smithsonian

Form Solid Mineral Deposits
Some minerals, given time and circumstance, form solid deposits. These solid mineral deposits are known as rock. Pressure, temperature, erosion, and friction are forces that effect the formation of rock. The rock formation process allows geologists to classify rock into three groups: sedimentary, igneous, and metamorphic. Sedimentary rock forms when layers of "sediment" (small particles of solid minerals like sand and pebbles) fuse together over time under the force of water or wind. Sedimentary rock is commonly found in and near riverbeds and streambeds. Igneous ("fire-formed") rock forms after minerals are heated to extremely high temperatures and then allowed to cool. Hawaii is a well-known source of igneous rock. Most igneous rock forms when hot molten lava cools to a solid state. Metamorphic rock forms when rock undergoes a transformation from one structure to another, usually caused by pressure, heat, and water. For example, a rock that is compacted to a more crystalline condition has undergone a metamorphosis.

These resources offer more information about the formation of rock.

Rocks and Minerals of Kentucky

Add Unusual Characteristics
Some rock formations develop the unusual property of fluorescence. The minerals in the rock give off radiation as visible light in certain circumstances. These fluorescent rock specimens show their behavior in three different lighting situations: normal cool light, longwave ultraviolet light, and shortwave ultraviolet light.

Fluorescent Rocks

Ken's Fluorescent Minerals

Cut and Polish Some Rock
Gemstones are rock or other fossilized organic materials (like amber below) that are cut and polished to a brilliant state. Gemstones possess certain characteristics that make them attractive and valuable. Optical properties and durability are two examples. If a gemstone can be cut such that it reflects light brilliantly it becomes valuable for its luster. Extremely strong gemstones are desired for their durability. A diamond, for example, has a high luster and a high durability. Therefore, the diamond has become valuable and has come to symbolize long enduring relationships.

The Rainbow of Gems

How are Gemstones Classified?

Fossilize Some Treesap
And then there's amber. Amber is the fossilized resin of ancient trees. Approximately thirty and ninety million years ago, sticky sap oozed from trees, catching insects, leaves, seeds, and other forest debris in a sticky trap. Over a long, long time, the sticky resin hardened into a solid fossilized deposit known as amber.

The World of Amber

Assume A Fixed and Definite Shape
Many minerals are capable of forming solid crystalline deposits. Crystals are formed when a mineral solidifies under force in such a way that the solid forms a regular repeating arrangement on both the external surface and the molecular level. Quartz, a transparent crystal of silica (sand), is an abundant crystal used for many purposes.

Introduction to Crystallography and Mineral Crystal Systems

Crystal Structure Movies

Frequently Asked Questions About Crystals

Sand

Consider Some Other Ideas
So we have all of this rock, now what do we do? Throughout human history, civilizations have invented ways to use rock to improve the quality of their lives. Coal mining is a recent case worth study. Powder River Coal Company in Gillette, Wyoming, is the second largest coal producing company in the United States. Consider the process, the reward, and the consequence.

Powder River Coal Company

Alone in the wilderness without matches or a lighter, you can rub two sticks together to create heat from friction that can cause a spark and light a campfire. Or, you can strike certain pieces of rock together to create a spark. If striking two small pieces of rock together can cause a spark, imagine what happens when two huge rock plates underneath continents bump into each other. The sparks really fly! Earthquakes, landslides, floods, and volcanic eruptions are a few possible results.

A Model of Three Faults

Every rock has a story to tell. A good geologist knows when to shut up and listen. Each rock has a long and winding history. The rock of the Ocoee River Gorge along US Highway 64 in the scenic Cherokee National Forest of southeastern Tennessee has been waiting millions of years to tell its story. So shut up and listen.

The Geologic Story of the Ocoee River

Teach Others About Rock
These educational resources offer suggestions for teaching others about the fascinating world of rock. The activities and lesson plans may enhance your traditional geology curriculum.

Atlas of Rocks and Minerals

Rock Classification

A Gem of a Story Activities

The best way to wrap your mind around rock, however, is to wrap your hands around rock. No matter which of these resources you decide to use in your study of rock and minerals, make sure you get outside and get your hands on some rock. Compare textures. Compare colors. Compare sizes. The rock will remember.

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