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USGS Geology in the Parks

Geologic Glossary

This glossary contains simplified definitions for technical terms used within this site.
For more complete, technical definitions, click here.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

J

joint

A narrow crack in rock along which there has been no significant movement of either side. Joints commonly form in parallel sets.

K

karst

A distinctive landscape (topography) that can develop where the underlying bedrock, often limestone or marble, is partially dissoved by surface or ground water.

kyanite

An aluminum-rich, blue to light green silicate mineral. Kyanite forms in metamorphic rocks at moderate temperature and high pressure.

L

lahar

A type of mudflow that originates on the slopes of volcanoes when volcanic ash and debris becomes saturated with water and flows rapidly downslope.

lamination

Very thin layers of less than 1 cm thickness.

landslide

Downslope movement of rock, soil, and mud.

land-use

Present and historical uses of land, such as for agriculture, mining, recreation and grazing.

lava

Magma that reaches the Earth's surface through a volcanic eruption. When cooled and solidified, forms extrusive (volcanic) igneous rock.

lawsonite

A metamorphic mineral that forms only under very high pressure. It is a calcium aluminum silicate and usually forms microscopic crystals.

lichenometry


A dating method that uses the growth rate of certain lichen species as an indicator of the age of the surface the lichen is growing on.

limestone

A sedimentary rock made mostly of the mineral calcite (calcium carbonate). Limestone is usually formed from shells of once-living organisms or other organic processes, but may also form by inorganic precipitation.

limonite

A mineral composed of iron oxides and water. Rust. Very common in many rocks after weathering at the Earth's surface. Imparts brown or yellow colors to many rocks.

lineament

A linear (relatively straight) topographic feature or features such as a fault, line of dense vegetation, or a chain of aligned volcanoes.

lineation

Parallel arrangement of elongate minerals or groups of minerals. To envision lineation, imagine packages of spaghetti or pencils.

lithic

"Made of stone". Refers to pieces of rock within other rocks such as tuff and conglomerate.

lithification

The conversion of loose sediment into solid sedimentary rock. Several processes, including compaction of grains, filling of spaces between grains with mineral cement, and crystallization act to solidify sediment.

lithosphere

The outer layer of solid rock that includes the crust and uppermost mantle. This layer, up to 100 kilometers (60 miles) thick, forms the Earth's tectonic plates. Tectonic plates float above the more dense, flowing layer of mantle called the asthenosphere.
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loess

A wind-blown deposit of sediment made mostly of silt-sized grains.

luster

The appearance of the reflection of light from the surface of a mineral. Luster is described as metallic, glassy, dull, etc.

 

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