Category: Rocks


Types of Rock Art: Petroglyphs and Pictographs Rocks

Types of Rock Art: Petroglyphs and Pictographs

Article by: Hobart M. King, Ph.D., RPG Petroglyphs on sandstone at Newspaper Rock in southwestern Utah. Image copyright iStockphoto / Jeremy Edwards. Petroglyph: This petroglyph is thought to have been carved by Native Americans into the wall of Buckskin Gulch in southern Utah, USA. Image copyright iStockphoto / amygdala_imagery.

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Pictograph Photo Gallery Rocks

Pictograph Photo Gallery

A pictograph is a drawing or painting that is created on a rock. It is not "carved" into the rock - that would be a "petroglyph." Cueva de las Manos (Spanish for Cave of the Hands) is a series of caves in Argentina where ancient people painted on the walls starting over 9,000 years ago. The wall above is one of many that is covered with hand silhouettes.

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The Most Difficult Rocks to Identify Rocks

The Most Difficult Rocks to Identify

Specimens that will challenge the most experienced geologist! Article by: Hobart M. King, Ph.D., RPG "What kind of rock is this?" Out of a million rocks on a beach, a child will select the most unusual. The geologist might be able to identify 99% of the rocks on that beach, but the child will probably pick from the exotic 1%.

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Skarn Rocks

Skarn

A metamorphic rock that has been altered by hot, chemically-active fluids. Article by: Hobart M. King, Ph.D., RPG Skarn: A specimen of skarn composed mainly of garnet, pyroxene, carbonate, and quartz. This specimen is approximately three inches across. What is Skarn? Skarn is a metamorphic rock that has been chemically and mineralogically altered by metasomatism.

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Chalk Rocks

Chalk

A marine limestone composed mainly of foraminifera and algal remains. Article by: Hobart M. King, Ph.D., RPG Limestone Chalk: A fine-grained, light-colored limestone chalk formed from the calcium carbonate skeletal remains of tiny marine organisms. What Is Chalk? Chalk is a variety of limestone composed mainly of calcium carbonate derived from the shells of tiny marine animals known as foraminifera and from the calcareous remains of marine algae known as coccoliths.

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Obsidian Rocks

Obsidian

What is Obsidian, How Does it Form, and What is it Used For? Article by: Hobart M. King, Ph.D., RPG Obsidian: The specimen shown above is about two inches (five centimeters) across. The curved semi-concentric ridges are breakage marks associated with obsidian's conchoidal fracture. The rock has very sharp edges.

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Amphibolite Rocks

Amphibolite

A metamorphic rock composed primarily of amphibole minerals and plagioclase feldspar Article by: Hobart M. King, Ph.D., RPG Amphibolite: Amphibolite is a coarse-grained metamorphic rock that has amphibole minerals such as the hornblende group as its primary ingredient. The specimen shown is about two inches (five centimeters) across.

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Basalt Rocks

Basalt

What Is Basalt, How Does It Form, and How Is It Used? Article by: Hobart M. King, Ph.D., RPG Basalt: A fine-grained igneous rock that is usually black in color. The specimen shown is about two inches (five centimeters) across. What is Basalt? Basalt is a dark-colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals.

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Iron Ore Rocks

Iron Ore

What Is Iron Ore, How Does It Form, and What Is It Used For? Article by: Hobart M. King, Ph.D., RPG Iron Ore: A specimen of oolitic hematite iron ore. The specimen shown is about two inches (five centimeters) across. What is Iron Ore? Earth's most important iron ore deposits are found in sedimentary rocks.

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Marble Rocks

Marble

A non-foliated metamorphic rock that forms when limestone is subjected to heat and pressure. Article by: Hobart M. King, Ph.D., RPG Pink Marble: A piece of pink marble about four inches (ten centimeters) across. The pink color is most likely derived from iron. Image by NASA. What is Marble? Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism.

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Dolomite Rocks

Dolomite

A sedimentary rock similar to limestone. Also known as "dolostone" and "dolomite rock." Article by: Hobart M. King, Ph.D., RPG "The Dolomites" are a mountain range in northeastern Italy and part of the Italian Alps. They are one of the largest exposures of dolomite rock on Earth - from which the name is obtained.

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Rocks on Mars Rocks

Rocks on Mars

A variety of rock types and sediments have been found on Mars. Many are similar to rocks on Earth. Mudstone: This photograph, taken by NASA's Mars Rover Curiosity in 2015, shows sedimentary rocks of the Kimberley Formation in Gale Crater. The crater contains thick deposits of finely laminated mudstone that represent fine-grained sediments deposited in a standing body of water that persisted for a long period of time - long enough to allow sediments to accumulate to significant thickness.

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Hornfels Rocks

Hornfels

A fine-grained contact metamorphic rock without obvious foliation. Article by: Hobart M. King, Ph.D., RPG Hornfels: Hornfels is a fine-grained metamorphic rock without obvious foliation. It forms during contact metamorphism at shallow depth. The specimen shown is about two inches (five centimeters) across.

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Chert Rocks

Chert

What Is Chert? How Does It Form? What Is It Used For? Article by: Hobart M. King, Ph.D., RPG Chert: This specimen of gray chert is about two inches (five centimeters) across. It breaks with a smooth conchoidal fracture. Edges of the piece have sharp edges as a result of the conchoidal fracture. What is Chert?

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Dacite Rocks

Dacite

An extrusive igneous rock intermediate between rhyolite and andesite. Article by: Hobart M. King, Ph.D., RPG Dacite: A piece of dacite from Mount General, San Bernardino County, California. This specimen is approximately four inches (ten centimeters) across. Click to enlarge. What Is Dacite? Dacite is a fine-grained igneous rock that is normally light in color.

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Trap Rock Rocks

Trap Rock

A construction industry term used for dark-colored igneous rocks used to make crushed stone. Article by: Hobart M. King, Ph.D., RPG Crushed Trap Rock ready for use in a construction project. Trap rock is any dark-colored igneous rock that is used to produce crushed stone. Image copyright Brilt and iStockphoto.

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Gabbro Rocks

Gabbro

What Is Gabbro, What Minerals Are In Gabbro, and What Is It Used For? Article by: Hobart M. King, Ph.D., RPG Gabbro is a dark-colored coarse-grained intrusive igneous rock. The specimen shown above is about two inches (five centimeters) across. What is Gabbro? Gabbro is a coarse-grained, dark-colored, intrusive igneous rock.

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Caliche Rocks

Caliche

Also known as calcrete, hardpan, and duricrust Article by: Hobart M. King, Ph.D., RPG Caliche: This specimen of caliche is composed of rounded rock fragments and fine-grained sediments, bound together with a calcium carbonate cement. What Is Caliche? "Caliche" is a shallow layer of soil or sediment in which the particles have been cemented together by the precipitation of mineral matter in their interstitial spaces.

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Pumice Rocks

Pumice

Article by: Hobart M. King, Ph.D., RPG Pumice: This specimen shows the frothy vesicular texture of pumice. It has a specific gravity of less than one and will float on water. It is about five centimeters (two inches) across. Pumice at Mount St. Helens: A pyroclastic flow will sometimes contain large pieces of pumice.

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Breccia Rocks

Breccia

What Is Breccia, How Does It Form, and What Is Its Composition? Article by: Hobart M. King, Ph.D., RPG Chert Breccia: The angular clasts in this breccia are chert fragments. The matrix is an iron-stained mix of clay- through sand-size particles. The specimen is about two inches (five centimeters) across.

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