Category: Rocks


Mariposite Rocks

Mariposite

An informal name used for green micas and a variety of rocks that contain them. Article by: Hobart M. King, Ph.D., RPG Mariposite: This is a rock that many people would call "mariposite" because it contains an abundance of green mica minerals. Photo by Robert Holland, used here under a Creative Commons license.

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Scoria Rocks

Scoria

Article by: Hobart M. King, Ph.D., RPG Scoria: A piece of scoria about 4 inches (10 centimeters) in diameter. A specimen with a rounded shape like this was most likely blown from a volcanic vent. This photograph was taken by Jonathan Zander and is used under a GNU Free Documentation License. What is Scoria?

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Siltstone Rocks

Siltstone

A clastic sedimentary rock composed of silt-size grains. Article by: Hobart M. King, Ph.D., RPG Siltstone Colors: Siltstone occurs in a wide variety of colors. It is usually gray, brown, or reddish brown. It can also be white, yellow, green, red, purple, orange, black, and other colors. The colors are a response to the composition of the grains, the composition of the cement, or stains from subsurface waters.

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Conglomerate Rocks

Conglomerate

What Is Conglomerate? How Does It Form? What Is It Used For? Article by: Hobart M. King, Ph.D., RPG Conglomerate: The specimen shown is about two inches (five centimeters) across. It is made up of chert and limestone clasts bound in a matrix of sand and clay. What is Conglomerate? Conglomerate is a clastic sedimentary rock that contains large (greater than two millimeters in diameter) rounded clasts.

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Lapis Lazuli Rocks

Lapis Lazuli

A metamorphic rock, gem material, and mineral pigment that obtains its blue color from the mineral lazurite. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Lapis Lazuli Gemstones: As a general rule, solid blue lapis or solid blue with a few grains of gold pyrite are the most desirable colors.

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Schist Rocks

Schist

A foliated metamorphic rock that contains abundant platy mineral grains. Article by: Hobart M. King, Ph.D., RPG Muscovite schist: The dominant visible mineral in this schist is muscovite. Its platy grains are aligned in a common orientation, and that allows the rock to be split easily in the direction of the grain orientation.

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Tuff Rocks

Tuff

An igneous rock that forms from the debris ejected by an explosive volcanic eruption. Article by: Hobart M. King, Ph.D., RPG Fish Canyon Tuff: Panoramic view of an outcrop of the Fish Canyon Tuff. The volcanic eruption(s) that produced this tuff occurred about 28 million years ago at the La Garita Caldera in southwestern Colorado.

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Sandstone Rocks

Sandstone

A clastic sedimentary rock composed of sand-size grains of mineral, rock, or organic material. Article by: Hobart M. King, Ph.D., RPG Sandstone: The specimen shown is about two inches (five centimeters) across. What is Sandstone? Sandstone is a sedimentary rock composed of sand-size grains of mineral, rock, or organic material.

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Brazil Oil-Shale Deposits Rocks

Brazil Oil-Shale Deposits

Reprint of: United States Geological Survey Scientific Investigations Report 2005-5294 By John R. Dyni Brazil Oil Shale Figure 3. Deposits of oil shale in Brazil. From Padula (1969, his fig. 1). Click to enlarge map. At least nine deposits of oil shale ranging from Devonian to Tertiary age have been reported in different parts of Brazil (Padula, 1969).

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Morocco Oil-Shale Deposits Rocks

Morocco Oil-Shale Deposits

Reprint of: United States Geological Survey Scientific Investigations Report 2005-5294 By John R. Dyni Morocco Oil Shale Map of oil-shale deposits in Morocco (locations after Bouchta, 1984). Click to enlarge map. Oil-shale deposits have been identified at ten localities in Morocco, the most important of which are Upper Cretaceous marinites, not unlike those of Egypt, Israel, and Jordan.

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Estonia and Sweden Oil-Shale Deposits Rocks

Estonia and Sweden Oil-Shale Deposits

Reprint of: United States Geological Survey Scientific Investigations Report 2005-5294 By John R. Dyni Estonia and Sweden Oil Shale Map of kukersite deposits in northern Estonia and Russia (locations after Kattai and Lokk, 1998; and Bauert, 1994). Also, areas of Alum Shale in Sweden (locations after Andersson and others, 1985).

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A Grain of Sand Picture Gallery Rocks

A Grain of Sand Picture Gallery

A gallery of interesting and colorful sand grains from around the world. Images and captions by Dr. Gary Greenberg, Author of A Grain of Sand The tip of a spiral shell has broken off and become a grain of sand. It is opalescent from the repeated tumbling action of the surf. Surrounding the shell fragment are five other sand grains, from top middle clockwise, (1) a pink shell fragment, (2) a foram, (3) a microscopic shell, (4) a volcanic melt, and (5) a bit of coral.

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Pegmatite Rocks

Pegmatite

An extreme igneous rock with large crystals and rare minerals Article by: Hobart M. King, Ph.D., RPG Pegmatite: Pegmatite is an igneous rock composed almost entirely of crystals that are over one centimeter in diameter. The specimen shown here is about two inches (five centimeters) across. Topaz on albite: A crystal of imperial topaz on an albite matrix from a pocket in the Katlang Pegmatite of Pakistan.

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Canada Oil-Shale Deposits Rocks

Canada Oil-Shale Deposits

Reprint of: United States Geological Survey Scientific Investigations Report 2005-5294 By John R. Dyni Canada Oil Shale Map of oil-shale deposits in Canada (locations after Macauley, 1981). Click to enlarge map. Canada's oil-shale deposits range from Ordovician to Cretaceous age and include deposits of lacustrine and marine origin; as many as 19 deposits have been identified (Macauley, 1981; Davies and Nassichuk, 1988).

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Flint, Chert, and Jasper Rocks

Flint, Chert, and Jasper

Names for Microcrystalline Quartz Article by: Hobart M. King, Ph.D., RPG Microcrystalline Quartz: Four varieties of microcrystalline quartz and names that might be used for them. Clockwise from top left: Chert, red jasper, novaculite, and flint. More detail on each of these below. Flint, Chert, and Jasper: Names for Microcrystalline Quartz Flint, chert, and jasper are names commonly used by geologists and by the general public for opaque specimens of microcrystalline quartz.

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Petroglyph Photo Gallery Rocks

Petroglyph Photo Gallery

A petroglyph is an image that is carved into a rock. This "carving" can produce a visible indentation in the rock or it can simply be the scratching away of a weathered surface to reveal unweathered material of a different color below. It is not a "drawing" or a "painting" - those are "pictographs." Petroglyphs: Ute petroglyphs from Arches National Park, Utah, USA.

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Coal Rocks

Coal

What Is Coal and How Does It Form? Article by: Hobart M. King, Ph.D., RPG Bituminous Coal: Bituminous coal is typically a banded sedimentary rock. In this photo you can see bright and dull bands of coal material oriented horizontally across the specimen. The bright bands are well-preserved woody material, such as branches or stems.

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Limestone Rocks

Limestone

What Is Limestone and How Is It Used? Article by: Hobart M. King, Ph.D., RPG Limestone: The specimen shown is about two inches (five centimeters) across. What is Limestone? Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO 3 ) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters.

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Australia Oil-Shale Deposits Rocks

Australia Oil-Shale Deposits

Reprint of: United States Geological Survey Scientific Investigations Report 2005-5294 By John R. Dyni Australia Oil Shale Map of oil shale deposits in Australia (locations after Crisp and others, 1987; and, Cook and Sherwood 1989). Click to enlarge map. The oil-shale deposits of Australia range from small and noneconomic to deposits large enough for commercial development.

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Israel and Jordan Oil-Shale Deposits Rocks

Israel and Jordan Oil-Shale Deposits

Reprint of: United States Geological Survey Scientific Investigations Report 2005-5294 By John R. Dyni Israel and Jordan Oil Shale Map of oil shale deposits in Israel (locations after Minster, 1994). Also, oil-shale deposits in Jordan (locations after Jaber and others, 1997; and, Hamarneh, 1998). Click to enlarge map.

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