Glossary

Amphibole

Fact Sheet:

Chemical Composition: A group of inosilicate minerals with a general formula (Ca, Na, K)₂–₃(Mg, Fe, Al)₅(Si, Al)₈O₂₂(OH, F)₂
Hardness: 5 to 6 on the Mohs scale
Crystal System: Monoclinic or orthorhombic
Color Varieties: Green, black, brown, yellow, blue
Major Localities: United States, Canada, Italy, Norway, and Japan
Common Uses: Geological research, asbestos (some forms), ornamental stone, and industrial materials

Introduction: Amphibole is a diverse group of minerals that includes several important rock-forming members. Known for their fibrous crystal habit and presence in both igneous and metamorphic rocks, amphiboles play a crucial role in understanding geological ...

^CColumnar Jointing

Columnar jointing is a geological structure that forms when a thick lava flow or shallow intrusive body cools and contracts, creating a pattern of polygonal columns, typically with a hexagonal cross-section. These columns are often vertical and can be seen in basaltic formations, such as the Giant’s Causeway in Northern Ireland. Columnar jointing is important in understanding the cooling and solidification processes of volcanic rocks.

Reference: De Graff, J. M., & Aydin, A. (1987). “Surface Morphology of Columnar Joints and Its Significance to Mechanism of Jointing.” Geological Society of America Bulletin, 99(5), 605-617.

^CConchoidal Fracture

Conchoidal fracture is a type of fracture that occurs in brittle materials, such as glass or quartz, where the breakage produces smooth, curved surfaces that resemble the interior of a seashell. This fracture pattern is characteristic of materials that lack natural planes of weakness, making it important in the identification of minerals and the study of material properties.

Reference: Klein, C., & Hurlbut, C. S. (1999). Manual of Mineralogy. Wiley.

^CContinental Divide

A continental divide is a natural boundary or ridge that separates the watersheds of major river systems on a continent. Water on either side of the divide flows to different oceans or basins. Continental divides are important in hydrology and geography, as they influence the flow of rivers and the distribution of water resources.

Reference: Hedman, E. R., & Osterkamp, W. R. (1982). “Streamflow Characteristics Related to Channel Geometry of Streams in Western United States.” Geological Survey Water-Supply Paper 2193.

^CContinental Drift

Continental drift is the hypothesis that the continents have moved across the Earth’s surface over geological time. Proposed by Alfred Wegener in 1912, this idea laid the groundwork for the modern theory of plate tectonics. Continental drift is critical in understanding the historical distribution of continents, the formation of mountain ranges, and the development of ocean basins.

Reference: Wegener, A. (1966). The Origin of Continents and Oceans. Dover Publications.

^CContinental Margin

The continental margin is the zone of the ocean floor that separates the thin oceanic crust from the thick continental crust. It includes the continental shelf, continental slope, and continental rise. Continental margins are key areas for studying sediment deposition, tectonic activity, and the interaction between land and ocean systems. They are also important for oil and gas exploration.

Reference: Carter, L., Carter, R. M., & McCave, I. N. (2004). “Evolution of the Sedimentary System on the Pacific Margin of Eastern New Zealand.” Marine Geology, 205(1-4), 9-27.

^CContinental Shelf

The continental shelf is the submerged, gently sloping edge of a continental landmass that extends from the shoreline to the continental slope. This area is rich in marine life and resources, including oil and gas deposits. The continental shelf is crucial in the study of marine geology, oceanography, and the exploration of natural resources.

Reference: Shepard, F. P. (1973). Submarine Geology. Harper & Row.

^CContinental Slope

The continental slope is the steeply inclined section of the continental margin that descends from the edge of the continental shelf to the continental rise. It marks the true edge of the continent, where the continental crust transitions to the oceanic crust. The study of continental slopes is crucial for understanding sediment transport, submarine landslides, and the dynamics of ocean currents.

Reference: Menard, H. W. (1964). Marine Geology of the Pacific. McGraw-Hill.

^CConvergent Boundary

A convergent boundary is a type of tectonic plate boundary where two plates move toward each other. At these boundaries, one plate is usually forced beneath the other in a process known as subduction. Convergent boundaries are associated with the formation of mountain ranges, deep ocean trenches, and volcanic activity. They are critical in understanding the processes of orogeny, subduction, and the recycling of oceanic crust into the mantle.

Reference: Stern, R. J. (2002). “Subduction Zones.” Reviews of Geophysics, 40(4), 1012.

^CCoral Reef

Coral reefs are marine ecosystems composed of reef-building corals, which are colonies of small, sessile animals known as polyps. These reefs are found in shallow, warm ocean waters and are vital for biodiversity, providing habitat for a vast array of marine life. Coral reefs are also important in the study of marine biology, ecology, and climate change, as they are sensitive indicators of environmental stress.

Reference: Spalding, M. D., Ravilious, C., & Green, E. P. (2001). World Atlas of Coral Reefs. University of California Press.

^CCoulomb’s Law

In geology, Coulomb’s law refers to a criterion used to describe the conditions under which a material will fail due to shear stress. It is based on the relationship between the shear stress and normal stress on a plane, along with the material’s internal friction and cohesion. This law is fundamental in understanding fault mechanics, rock stability, and landslide processes.

Reference: Jaeger, J. C., Cook, N. G. W., & Zimmerman, R. (2007). Fundamentals of Rock Mechanics. Wiley-Blackwell.

^CCrater Lake

A crater lake is a body of water that occupies a volcanic crater or caldera. These lakes can form in the depressions left by volcanic eruptions, meteorite impacts, or explosions. Crater lakes are often used in the study of volcanic activity, geochemistry, and hydrology, as they can provide insights into the volcanic history and ongoing processes in the region.

Reference: Bacon, C. R., & Lanphere, M. A. (2006). “Eruptive History and Geochronology of Mount Mazama and the Crater Lake Region, Oregon.” Geological Society of America Bulletin, 118(11-12), 1331-1359.

^CCraton

A craton is a large, stable block of the Earth’s crust that forms the ancient, central core of a continent. Cratons are composed of Precambrian rocks that have remained relatively undisturbed by tectonic activity for billions of years. They are significant in the study of geology as they represent the oldest and most stable parts of the Earth’s lithosphere, providing insights into the early history of the planet.

Reference: Bleeker, W. (2003). “The Late Archean Record: A Puzzle in ca. 35 Pieces.” Lithos, 71(2-4), 99-134.

^CCratonic Basin

A cratonic basin is a large, stable sedimentary basin that forms on a craton, the ancient, stable core of a continent. These basins are typically characterized by long periods of subsidence, leading to the accumulation of thick sedimentary sequences. Cratonic basins are significant for studying the history of sedimentation, tectonics, and natural resource deposits, including oil and gas.

Reference: Sloss, L. L. (1963). “Sequences in the Cratonic Interior of North America.” Geological Society of America Bulletin, 74(2), 93-114.

^CCross-Bedding

Cross-bedding is a sedimentary structure characterized by inclined layers within a horizontal bed, formed by the movement of sediment by wind or water. These structures are commonly found in environments like rivers, deltas, and deserts. Cross-bedding is important for interpreting past flow conditions, sediment transport, and the depositional environment in which the sediment was laid down.

Reference: Allen, J. R. L. (1982). Sedimentary Structures: Their Character and Physical Basis. Elsevier.

^CCross-Cutting Relationships

Cross-cutting relationships are a principle of geology that states that any geological feature that cuts across another is younger than the feature it cuts. This principle is fundamental in establishing the relative ages of rocks and geological structures, and is widely used in stratigraphy, tectonics, and the interpretation of geological history.

Reference: Ramsay, J. G., & Huber, M. I. (1987). The Techniques of Modern Structural Geology, Volume 2: Folds and Fractures. Academic Press.

^CCryoconite

Cryoconite is a dark, granular material found on glacier surfaces, composed of dust, soot, and other fine debris, often mixed with microbial communities. It absorbs solar radiation, leading to localized melting of the ice and the formation of small depressions called cryoconite holes. Cryoconite is important in the study of glacial environments, as it influences the albedo and melting rates of glaciers.

Reference: Hodson, A. J., Anesio, A. M., Ng, F., Watson, R., Quirk, J., Irvine-Fynn, T., & Sattler, B. (2007). “A Glacier Respires: Quantifying the Distribution and Respiration of Cryoconite Across an Entire Arctic Supraglacial Ecosystem.” Journal of Geophysical Research: Biogeosciences, 112(G4).

^CCryosphere

The cryosphere encompasses all the Earth’s frozen water, including glaciers, ice caps, ice sheets, sea ice, snow, and permafrost. The cryosphere plays a critical role in regulating the Earth’s climate by reflecting solar radiation and influencing sea levels. Understanding the cryosphere is essential for studying climate change, hydrology, and global sea-level rise.

Reference: IPCC (2019). The Ocean and Cryosphere in a Changing Climate. Intergovernmental Panel on Climate Change Special Report.

^CCuesta

A cuesta is a ridge with a gentle slope on one side and a steep slope on the other, typically formed by the differential erosion of tilted sedimentary rock layers. The gentle slope corresponds to the dip of the strata, while the steep slope is the scarp face. Cuestas are common in areas of gently folded sedimentary rocks and are important in understanding the processes of erosion and landscape development.

Reference: Baker, V. R., & Twidale, C. R. (1991). “The Elucidation of Landform Assemblages and Their Genesis.” Geological Society of America Bulletin, 103(9), 1166-1177.

^CCut Bank

A cut bank is the outside bank of a meander in a river, where erosion is actively occurring due to the higher velocity of water flow. Cut banks are important features in the study of fluvial geomorphology and river dynamics, as they contribute to the lateral migration of rivers and the formation of meandering channels.

Reference: Leopold, L. B., Wolman, M. G., & Miller, J. P. (1964). Fluvial Processes in Geomorphology. Dover Publications.

^CCyclothem

A cyclothem is a repeating sequence of sedimentary rock layers that represents alternating marine and non-marine conditions, typically associated with the cyclic rise and fall of sea levels. Cyclothems are important in the study of stratigraphy and sedimentology, particularly in understanding the depositional environments of coal-bearing sequences.

Reference: Heckel, P. H. (1986). “Sea-Level Curve for Pennsylvanian Eustatic Marine Transgressive-Regressive Depositional Cycles along Midcontinent Outcrop Belt, North America.” Geology, 14(4), 330-334.

^DDebris Cone

A debris cone is a conical accumulation of rock fragments, soil, and other debris that has been transported downslope by gravity, water, or ice. These cones often form at the base of cliffs, slopes, or glaciers and are important for understanding mass-wasting processes, sediment transport, and the geomorphology of mountainous regions.

Reference: Whalley, W. B., & Azizi, F. (2003). “Rock Glaciers and Protalus Forms: Analogous Forms and Equifinal Processes?” Geografiska Annaler: Series A, Physical Geography, 85(3-4), 237-249.

^DDebris Flow

A debris flow is a fast-moving mass of loose mud, sand, soil, rock, and water that flows down a slope, typically triggered by heavy rainfall, volcanic activity, or rapid snowmelt. Debris flows are highly destructive and pose significant hazards in mountainous regions. They are important in the study of mass wasting, geomorphology, and natural hazards.

Reference: Iverson, R. M. (1997). “The Physics of Debris Flows.” Reviews of Geophysics, 35(3), 245-296.

^DDecompression Melting

Decompression melting occurs when a body of rock ascends in the Earth’s mantle, leading to a decrease in pressure while the temperature remains nearly constant, allowing the rock to melt. This process is significant in the formation of mid-ocean ridge basalts, hotspot volcanism, and continental rift zones, contributing to the generation of new crust.

Reference: McKenzie, D., & Bickle, M. J. (1988). “The Volume and Composition of Melt Generated by Extension of the Lithosphere.” Journal of Petrology, 29(3), 625-679.

^XArchives: Glossary

The X-ray absorption coefficient is a measure of how easily a material absorbs X-rays, which is used to determine the composition and density of materials in X-ray imaging techniques. This coefficient is significant in geophysics, mineralogy, and materials science for understanding the properties of rocks, minerals, and other materials in non-destructive testing and imaging.

Reference: Jenkins, R. (1999). “X-ray Fluorescence Spectrometry.” Wiley-Interscience.

Rocks

Glossary

C

Columnar Jointing

C

Conchoidal Fracture

C

Continental Divide

C

Continental Drift

C

Continental Margin

C

Continental Shelf

C

Continental Slope

C

Convergent Boundary

C

Coral Reef

C

Coulomb’s Law

C

Crater Lake

C

Craton

C

Cratonic Basin

C

Cross-Bedding

C

Cross-Cutting Relationships

C

Cryoconite

C

Cryosphere

C

Cuesta

C

Cut Bank

C

Cyclothem

D

Debris Cone

D

Debris Flow

D

Decompression Melting

Amphibole

CColumnar Jointing

CConchoidal Fracture

CContinental Divide

CContinental Drift

CContinental Margin

CContinental Shelf

CContinental Slope

CConvergent Boundary

CCoral Reef

CCoulomb’s Law

CCrater Lake

CCraton

CCratonic Basin

CCross-Bedding

CCross-Cutting Relationships

CCryoconite

CCryosphere

CCuesta

CCut Bank

CCyclothem

DDebris Cone

DDebris Flow

DDecompression Melting

XArchives: Glossary