Appendix 1. Terms and Definitions for the GeoMaterial and GeoMaterialConfidence Fields

Overview

Much of the benefit from a defined database schema depends on use of clearly defined vocabularies. On the basis of many discussions within the geoscience community over the past three decades, it seems to be the consensus (and a logical conclusion) that users of geologic map databases are best served if certain terminology, particularly for lithology, is consistent from one database to another. Such a list of terms commonly is referred to as a controlled-term list or a vocabulary.

The terms that populate the GeoMaterial and GeoMaterialConfidence fields in the DescriptionOfMapUnits table constitute such a controlled-term list. These terms are defined below, and they are encapsulated in a database table (see table 17) generated by the script GeMS_CreateDatabase_Arc10.py (or its replacement), available at the GeMS Toolkit site on GitHub (https://github.com/usgs/GeMS_Tools or https://github.com/usgs/gems-tools-pro). The table is also available as an Excel spreadsheet under the Resources heading at the GeMS website (https://ngmdb.usgs.gov/Info/standards/GeMS/); the spreadsheet also includes the field HierarchyKey to facilitate sorting.

Scope and Intent

This classification of materials is intended to characterize a map unit by means of a generalized category (GeoMaterial) based on lithologic and genetic criteria; it applies to the map unit as a whole. The purposes of this classification are to provide a basis for quickly integrating map data from different sources and to convey to the public a simple, general sense of each map unit’s lithology and genesis. We recognize that such a classification cannot completely address the immense variety of map units present across the Nation, and we expect that other regionally specific classifications of map units will be developed that are more appropriate to local conditions. The appropriateness of a selected GeoMaterial term for describing a map unit is specified by values in the GeoMaterialConfidence field (see table 1–1), which provide the map user with a potentially useful qualifier term (please refer to the Geologic Materials discussion in the “Design Considerations” section, above).

Table 1-1. Values (and their definitions) that populate the GeoMaterialConfidence field in a DescriptionOfMapUnits table.
[Note that, when creating a new database, the script GeMS_CreateDatabase_Arc10.py (available at https://github.com/usgs/GeMS_Tools) or its replacement inserts these GeoMaterialConfidence terms and definitions into Glossary table. See also, table 14]

GeoMaterial Terms

The lithologic terms in the GeoMaterial field and their definitions are provided below, and their hierarchy is represented by an indented format for clarity. Documentation of this classification, including rationale for its development, was provided in Soller (2009); some terms and definitions in that classification were updated for version 1.1 of GeneralLithology (see “Archive of Previous Versions and Related Information” section at https://ngmdb.usgs.gov/Info/standards/GeMS/). In the nine years of test implementation among the state geological surveys and USGS, this classification was slightly modified for GeMS, and renamed as “GeoMaterial”. The current version of this classification is maintained at the GeMS website.

The following is GeMS’ vocabulary of GeoMaterial terms (shown in bold type) and their definitions:

• Sedimentary material — An aggregation of particles deposited by gravity, air, water, or ice, or as accumulated by other natural agents operating at Earth’s surface such as chemical precipitation or secretion by organisms. May include unconsolidated material (sediment) and (or) sedimentary rock. Does not include sedimentary material directly deposited as a result of volcanic activity.
• Sediment — Unconsolidated material (sediment) composed of particles deposited by gravity, air, water, or ice, or as accumulated by other natural agents operating at Earth’s surface such as chemical precipitation or secretion by organisms. Does not include sedimentary material directly deposited as a result of volcanic activity.
• Clastic sediment — Sediment formed by weathering and erosion of preexisting rocks or minerals; eroded particles or “clasts” are transported and deposited by gravity, air, water, or ice.
• Sand and gravel of unspecified origin — Sediment composed mostly of sand and (or) gravel, formed by weathering and erosion of preexisting rocks or minerals; eroded particles or “clasts” are transported and deposited by gravity, air, water, or ice.
• Silt and clay of unspecified origin — Sediment composed mostly of silt and (or) clay, formed by weathering and erosion of preexisting rocks or minerals; eroded particles or “clasts” are transported and deposited by gravity, air, water, or ice.
• Alluvial sediment — Unconsolidated material deposited by streams or other bodies of running water as sorted or semisorted sediment in streambed, or on its floodplain or delta, or as cone or fan at base of mountain slope. Grain size varies from clay to gravel.
• Alluvial sediment, mostly coarse-grained — Unconsolidated material deposited by streams or other bodies of running water as sorted or semisorted sediment in streambed, or on its floodplain or delta, or as cone or fan at base of mountain slope. Sediment is mostly sand, gravel, and coarser material but may also contain some silt and clay.
• Alluvial sediment, mostly fine-grained — Unconsolidated material deposited by streams or other bodies of running water as sorted or semisorted sediment in streambed, or on its floodplain or delta, or as cone or fan at base of mountain slope. Sediment is mostly silt and clay but may also contain some sand and gravel.
• Glacial till — Mostly unsorted and unstratified material, generally unconsolidated, deposited directly by and underneath or adjacent to glacier without subsequent reworking by meltwater. Consists of heterogeneous mixture of clay, silt, sand, gravel, and boulders, ranging widely in size and shape.
• Glacial till, mostly sandy — Mostly unsorted and unstratified material, generally unconsolidated, deposited directly by and underneath or adjacent to glacier without subsequent reworking by meltwater. Consists of heterogeneous mixture of clay, silt, sand, gravel, and boulders, ranging widely in size and shape. Relatively sandy in texture.
• Glacial till, mostly silty — Mostly unsorted and unstratified material, generally unconsolidated, deposited directly by and underneath or adjacent to glacier without subsequent reworking by meltwater. Consists of heterogeneous mixture of clay, silt, sand, gravel, and boulders, ranging widely in size and shape. Relatively loamy (silty) in texture.
• Glacial till, mostly clayey — Mostly unsorted and unstratified material, generally unconsolidated, deposited directly by and underneath or adjacent to glacier without subsequent reworking by meltwater. Consists of heterogeneous mixture of clay, silt, sand, gravel, and boulders, ranging widely in size and shape. Relatively clayey in texture.
• Ice-contact and ice-marginal sediment — Mostly sand-, silt-, and gravel-sized particles or “clasts” derived from rock or preexisting sediment that has been eroded and transported by glaciers. As glacier melted, material was deposited by running water essentially in contact with glacial ice or was transported and deposited by glacially fed streams. Includes sediment deposited into water bodies adjacent to glacier.
• Ice-contact and ice-marginal sediment, mostly coarse-grained — Mostly sand- and gravel-sized particles or “clasts”, with lesser amounts of silt and clay, derived from rock or preexisting sediment that has been eroded and transported by glaciers. As glacier melted, material was deposited by running water essentially in contact with glacial ice or was transported and deposited by glacially fed streams. Includes sediment deposited into water bodies adjacent to glacier.
• Ice-contact and ice-marginal sediment, mostly fine-grained — Mostly silt- and clay-sized particles or “clasts”, with lesser amounts of sand and gravel, derived from rock or preexisting sediment that has been eroded and transported by glaciers. As glacier melted, material was deposited by running water essentially in contact with glacial ice or was transported and deposited by glacially fed streams. Includes sediment deposited into water bodies adjacent to glacier.
• Eolian sediment — Silt- and sand-sized sediment, deposited by wind.
• Dune sand — Mostly sand-sized sediment, deposited by wind. Typically characterized by various dune landforms.
• Loess — Silty sediment, deposited by wind, commonly near glacial margin.
• Lacustrine sediment — Mostly well-sorted and well-bedded material that ranges in grain size from clay to gravel, deposited in perennial to intermittent lakes. Much of sediment is derived from material eroded and transported by streams. Includes deposits of lake-marginal beaches and deltas.
• Lacustrine sediment, mostly coarse-grained — Mostly well-sorted and well-bedded material, generally sand and gravel sized, with lesser amounts of silt and clay, deposited in perennial to intermittent lakes. Much of sediment is derived from material eroded and transported by streams. Mostly deposits of lake-marginal beaches and deltas.
• Lacustrine sediment, mostly fine-grained — Mostly well-sorted and well-bedded material, generally silt and clay sized, with lesser amounts of sand, deposited in perennial to intermittent lakes.
• Playa sediment — Fine-grained clastic sediment and evaporitic salts, deposited in ephemeral lakes in centers of undrained basins. Includes material deposited in playas, mud flats, salt flats, and adjacent saline marshes. Generally interbedded with eolian sand and with lacustrine sediment deposited during wetter climatic periods; commonly intertongues upslope with sediment deposited by alluvial fans.
• Coastal zone sediment — Mud and sand, with lesser amounts of gravel, deposited on beaches, on barrier islands, or in nearshore-marine, deltaic, or various low-energy shoreline (mud flat, tidal flat, sabka, algal flat) environments.
• Coastal zone sediment, mostly coarse-grained — Mostly sand, silt, and gravel, deposited on beaches, in dunes, and in shallow-marine and related alluvial environments.
• Coastal zone sediment, mostly fine-grained — Mostly clay and silt, deposited in lagoons, tidal flats, backbarriers, and coastal marshes.
• Marine sediment — Mud and sand, deposited in various marine environments. May originate from erosion of rocks and sediment or may be derived from marine organisms (of carbonate or siliceous composition).
• Marine sediment, mostly coarse-grained — Mud, sand, and gravel eroded from rocks and sediment on land, transported by streams, and deposited in marine deltas and basins. Mostly siliceous in composition.
• Marine sediment, mostly fine-grained — Mostly clay- and silt-sized sediment, deposited in relatively deep, quiet water, far removed from areas where coarser grained clastic sediments are washed into marine environment. Includes sediment derived from marine organisms.
• Mass movement sediment — Sediment formed by downslope transport of particles or “clasts” produced by weathering and breakdown of underlying rock, sediment, and (or) soil. Composed of poorly sorted and poorly stratified material that ranges in size from clay to boulders. Includes colluvial, landslide, talus, and rock-avalanche deposits.
• Colluvium and other widespread mass-movement sediment — Sediment formed by slow, relatively widespread, downslope transport of particles or “clasts” produced by weathering and breakdown of underlying rock, sediment, and (or) soil. Composed of poorly sorted and poorly stratified material that ranges in size from clay to boulders.
• Debris flows, landslides, and other localized mass-movement sediment — Sediment formed by relatively localized, downslope transport of particles or “clasts” produced by weathering and breakdown of underlying rock, sediment, and (or) soil. Composed of poorly sorted and poorly stratified material that ranges in size from clay to boulders. Speed of downslope transport ranges from rapid to imperceptible.
• Residual material — Unconsolidated material, developed in place by weathering of underlying rock or sediment. Usually forms relatively thin surface layer that conceals unweathered or partly altered source material. Material from which soils are formed.
• Carbonate sediment — Sediment formed by biotic or abiotic precipitation from aqueous solution of carbonates of calcium, magnesium, or iron (for example, limestone, dolomite).
• Peat and muck — Unconsolidated material, principally composed of plant remains, with lesser amounts of fine-grained clastic sediment. Deposited in water-saturated environment such as swamp, marsh, or bog. With lithification, such material becomes coal.
• Sedimentary rock — Consolidated material (rock) composed of particles transported and deposited by gravity, air, water, or ice, or accumulated by other natural agents operating at Earth’s surface, such as chemical precipitation or secretion by organisms. Does not here include sedimentary material directly deposited as result of volcanic activity.
• Clastic sedimentary rock — Sedimentary rock, composed predominantly of particles or “clasts” derived by erosion, weathering, or mass-wasting of preexisting rock and deposited by gravity, air, water, or ice.
• Conglomerate — Sedimentary rock, composed predominantly of particles or “clasts” derived by erosion and weathering of preexisting rock; contains more than 30 percent gravel-sized clasts.
• Sandstone — Sedimentary rock, composed predominantly of particles or “clasts” derived by erosion and weathering of preexisting rock; consists mostly of sand-sized particles, with or without fine-grained matrix of silt or clay.
• Mostly sandstone — Mostly sandstone, interbedded with other sedimentary rocks that locally may include conglomerate and finer grained clastic rocks (mudstone), carbonates, and (or) coal.
• Sandstone and mudstone — Sandstone and mudstone (including shale and siltstone), in approximately equal (or unspecified) proportions.
• Mudstone — Sedimentary rock, composed predominantly of particles or “clasts” derived by erosion and weathering of preexisting rock; consists mostly of mud (that is, silt- and clay-sized particles). Includes shale and siltstone.
• Mostly mudstone — Mostly mudstone, interbedded with other sedimentary rocks that locally may include coarser grained clastic rocks (sandstone, conglomerate), carbonates, and (or) coal.
• Carbonate rock — Sedimentary rock, consisting chiefly of carbonate minerals such as limestone or dolomite.
• Limestone — Carbonate sedimentary rock, consisting chiefly of calcite.
• Dolomite — Carbonate sedimentary rock, consisting chiefly of dolomite. Although “dolostone” is the proper analog to “limestone”, it has not often been applied to dolomitic units.
• Mostly carbonate rock — Mostly carbonate rock, interbedded with other sedimentary rock types.
• Chert — Sedimentary rock, composed chiefly of microcrystalline or cryptocrystalline quartz.
• Evaporitic rock — Sedimentary rock, composed primarily of minerals produced by evaporation of saline solution. Examples include gypsum, anhydrite, other diverse sulfates, halite (rock salt), primary dolomite, and rocks composed of various nitrates and borates.
• Iron-rich sedimentary rock — Sedimentary rock, in which at least half (by volume) of observed minerals are iron bearing (hematite, magnetite, limonite group minerals, siderite, iron sulfides).
• Coal and lignite — Organic-rich sedimentary rock, formed from compaction and alteration of plant remains. Coal is consolidated, harder, black rock. Lignite is semiconsolidated, brown to black, earthy material that may contain large particles of recognizable plant parts and tends to crack upon drying.
• Sedimentary and extrusive igneous material — Either (1) sedimentary rock and (or) unconsolidated material (sediment) and extrusive igneous material (volcanic rock and [or] sediment) or (2) volcanic rock and (or) sediment and such material after erosion and redeposition.
• Igneous rock — Rock and fragmental material that solidified from molten or partly molten material (magma).
• Extrusive igneous material — Molten material that was erupted onto Earth’s surface, fusing into rock or remaining as unconsolidated particles. Includes pyroclastic flows, air-fall tephra, lava flows, and volcanic mass flows.
• Volcaniclastic (fragmental) material — Rock and unconsolidated material consisting of particles or “clasts” that were formed by volcanic explosion or aerial expulsion from volcanic vent.
• Pyroclastic flows — Hot ash, pumice, and rock fragments erupted from volcano or caldera. Material moves downslope commonly in chaotic flows; once deposited, hot fragments may compact under their own weight and weld together.
• Felsic-composition pyroclastic flows — Hot ash, pumice, and rock fragments erupted from volcano or caldera. Material moves downslope commonly in chaotic flows; once deposited, hot fragments may compact under their own weight and weld together. Because of their high-silica content and resulting high viscosity, parental magmas tend to erupt explosively. Includes rhyolite, dacite, trachyte, latite; rocks are commonly lightcolored.
• Intermediate-composition pyroclastic flows — Hot ash, pumice, and rock fragments erupted from volcano. Material moves downslope commonly in chaotic flows; once deposited, hot fragments may compact under their own weight and weld together. Parental magma commonly erupts from stratovolcanoes as thick lava flows but also can generate strong explosive eruptions to form pyroclastic flows. Includes rocks that are, in color and mineral composition, intermediate between felsic and mafic rocks (for example, andesite).
• Mafic-composition pyroclastic flows — Hot ash, pumice, and rock fragments erupted from volcano. Material moves downslope commonly in chaotic flows; once deposited, hot fragments may compact under their own weight and weld together. Because of their low silica content and resulting low viscosity, parental magmas tend to erupt gently as lava flows rather than more forcefully as pyroclastic flows. Includes basalt; rocks are commonly dark-colored.
• Air-fall tephra — Fragments of volcanic rock and lava, of various sizes, carried into air by explosions and by hot gases in eruption columns or lava fountains; known as tephra. As tephra falls to ground, with increasing distance from volcano, average size of individual rock particles and thickness of resulting deposit decrease. Fine tephra deposited at some distance from volcano is known as volcanic ash.
• Felsic-composition air-fall tephra — Fragments of volcanic rock and lava, of various sizes, carried into air by explosions and by hot gases in eruption columns or lava fountains; known as tephra. As tephra falls to ground, with increasing distance from volcano, average size of individual rock particles and thickness of resulting deposit decrease. Because of their high silica content and resulting high viscosity, felsic-composition magmas tend to erupt explosively, readily forming pumice and volcanic ash. Composed of light-colored rocks (for example, rhyolite, dacite, trachyte, latite).
• Intermediate-composition air-fall tephra — Fragments of volcanic rock and lava, of various sizes, carried into the air by explosions and by hot gases in eruption columns or lava fountains; known as tephra. As tephra falls to ground, with increasing distance from volcano, average size of individual rock particles and thickness of resulting deposit decrease. Parental magma commonly erupts from stratovolcanoes as thick lava flows but also can generate strong explosive eruptions to form pyroclastic flows. Includes rocks that are, in color and mineral composition, intermediate between felsic and mafic rocks (for example, andesite).
• Mafic-composition air-fall tephra — Fragments of volcanic rock and lava, of various sizes, carried into the air by explosions and by hot gases in eruption columns or lava fountains; known as tephra. As tephra falls to ground, with increasing distance from volcano, average size of individual rock particles and thickness of resulting deposit decrease. Because of their low silica content and resulting low viscosity, parental magmas tend to erupt gently as lava flows, and so these deposits are uncommon. Includes basalt; rocks are commonly dark-colored.
• Lava flows — Lateral, surficial outpourings of molten lava from vent or fissure; also, solidified bodies of rock that form when they cool. Composed generally of fine-grained, dark-colored rocks (for example, basalt), which tend to form extensive sheets that have generally low relief, except in vent areas where cinder cones or shield volcanoes may form. Includes basaltic shield volcanoes, which may become very large (for example, Hawaii).
• Felsic-composition lava flows — Lateral, surficial outpourings of molten lava from vent or fissure; also, solidified bodies of rock that form when they cool. Because of their high silica content and resulting high viscosity, parental magmas tend to erupt explosively, and so these deposits are uncommon. Includes fine-grained, lightcolored rock with rhyolitic, dacitic, trachytic, and latitic composition.
• Intermediate-composition lava flows — Lateral, surficial outpourings of molten lava from vent or fissure; also, solidified bodies of rock that form when they cool. Parental magma commonly erupts from stratovolcanoes as thick lava flows. Includes rocks that are, in color and in mineral composition, intermediate between felsic and mafic rocks (for example, andesite).
• Mafic-composition lava flows — Lateral, surficial outpourings of molten lava from vent or fissure; also, solidified bodies of rock that form when they cool. Low-silica parental magmas have low viscosity and tend to form extensive sheets that have generally low relief. Includes basaltic shield volcanoes, which may become very large (for example, in Hawaii). Composed of fine-grained, dark rocks, including basaltic.
• Volcanic mass flow — Volcanic deposits formed by mass movement (for example, debris avalanches, debris flows, lahar deposits), in many cases triggered by volcanic eruption. Debris avalanches that occur on volcanoes clearly without eruptive trigger may be classified as sedimentary (for example, as “Debris flows, landslides, and other localized mass-movement sediment”).
• Intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) below Earth’s surface.
• Coarse-grained intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at some depth beneath Earth’s surface, thereby cooling slowly enough for mineral crystals to grow large enough to be visible to naked eye.
• Coarse-grained, felsic-composition intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at some depth beneath Earth’s surface, thereby cooling slowly enough for mineral crystals to grow large enough to be visible to naked eye. Composed mostly of light-colored minerals (for example, feldspar, quartz). Includes granitic, syenitic, and monzonitic rock.
• Coarse-grained, intermediate-composition intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at some depth beneath Earth’s surface, thereby cooling slowly enough for mineral crystals to grow large enough to be visible to naked eye. Intermediate in color and in mineral composition (between felsic and mafic igneous rock). Includes dioritic rock.
• Coarse-grained, mafic-composition intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at some depth beneath Earth’s surface, thereby cooling slowly enough for mineral crystals to grow large enough to be visible to naked eye. Composed mostly of feldspar and dark-colored minerals. Includes gabbroic rock.
• Ultramafic intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at some depth beneath Earth’s surface, thereby cooling slowly enough for mineral crystals to grow large enough to be visible to naked eye. Composed almost entirely of mafic minerals (for example, hypersthene, augite, olivine).
• Fine-grained intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at shallow depth beneath Earth’s surface, thereby cooling quickly. Generally fine grained but may contain large mineral crystals (phenocrysts). Mostly found as tabular dikes or sills.
• Fine-grained, felsic-composition intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at shallow depth beneath Earth’s surface, thereby cooling quickly. Generally fine grained but may contain large mineral crystals (phenocrysts). Mostly found as tabular dikes or sills. Composed mostly of light-colored minerals. Includes rhyolitic, dacitic, trachytic, and latitic rock.
• Fine-grained, intermediate-composition intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at shallow depth beneath Earth’s surface, thereby cooling quickly. Generally fine grained but may contain large mineral crystals (phenocrysts). Mostly found as tabular dikes or sills. Intermediate in color and in mineral composition (between felsic and mafic igneous rock). Includes andesitic rock.
• Fine-grained, mafic-composition intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) at shallow depth beneath Earth’s surface, thereby cooling quickly. Generally fine grained but may contain large mineral crystals (phenocrysts). Mostly found as tabular dikes or sills. Composed mostly of dark-colored minerals. Includes basaltic rock.
• Exotic-composition intrusive igneous rock — Rock that solidified from molten or partly molten material (magma) below Earth’s surface that has exotic mineralogical, textural, or field setting characteristics. Typically dark colored with abundant phenocrysts. Includes kimberlite, lamprophyre, lamproite, and foiditic rocks.
• Igneous and metamorphic rock — Consists of coarse-grained intrusive igneous rock and generally medium- to highgrade metamorphic rock.
• Metamorphic rock — Rock derived from preexisting rocks and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust.
• Regional metamorphic rock, of unspecified origin — Rock derived from preexisting rocks and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to marked regional changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Origin of preexisting rock is mixed (for example, igneous and sedimentary) or is not known.
• Lower-grade metamorphic rock, of unspecified origin — Rock derived from preexisting rocks and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to relatively mild regional changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Origin of preexisting rock is mixed (for example, igneous and sedimentary) or is not known. Includes slate and phyllite.
• Medium and high-grade regional metamorphic rock, of unspecified origin — Rock derived from preexisting rocks and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to relatively intense regional changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Origin of preexisting rock is mixed (for example, igneous and sedimentary) or is not known. Includes amphibolite, granulite, schist, and gneiss.
• Contact-metamorphic rock — Altered rock that originated by local processes of thermal metamorphism, genetically related to intrusion and extrusion of magmas and taking place at or near contact with body of igneous rock. Metamorphic changes are affected by heat and fluids emanating from magma and by some deformation because of emplacement of igneous mass.
• Deformation-related metamorphic rock — Rock derived from preexisting rocks by essentially solid-state mineralogical, chemical, or structural changes in response to strong deformation, commonly in association with marked changes in temperature, pressure, and (or) chemical environment. Generally forms in narrow, planar zones of local deformation (for example, along faults); characterized by foliation or alignment of mineral grains. Includes mylonite and cataclasite.
• Metasedimentary rock — Rock derived from preexisting sedimentary rocks and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust.
• Slate and phyllite, of sedimentary-rock origin — Fine-grained rock derived from preexisting sedimentary rocks and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Includes phyllite and slate (compact, fine-grained rock that possesses strong cleavage and, hence, can be split into slabs and thin plates). Mostly formed from fine-grained material such as mudstone.
• Schist and gneiss, of sedimentary-rock origin — Foliated rock derived from preexisting sedimentary rocks by essentially solid-state mineralogical, chemical, or structural changes in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Includes schist (characterized by such strong foliation or alignment of minerals that it readily splits into flakes or slabs) and gneiss (characterized by alternating, irregular bands of different mineral composition). Mostly formed from fine-grained material such as mudstone.
• Meta-carbonate rock — Rock derived from preexisting carbonate sedimentary rocks and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Characterized by recrystallization of carbonate minerals in source rock. Includes marble (for which preexisting rock was dominantly limestone or other rock composed of calcite), dolomitic marble, meta-dolostone, and meta-dolomite (for which preexisting rock contained appreciable amount of magnesium).
• Quartzite — Rock derived from preexisting quartz-rich sedimentary rocks (commonly sandstone) and altered by essentially solid-state mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, shear stress, and (or) chemical environment, generally at depth in Earth’s crust.
• Metaigneous rock — Rock derived from preexisting igneous rocks and altered by essentially solid-state, mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, shear stress, and (or) chemical environment, generally at depth in Earth’s crust.
• Meta-ultramafic rock — Rock derived from preexisting ultramafic rocks by essentially solid-state, mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Composed mostly of magnesium-bearing minerals (for example, serpentine, talc, magnesite).
• Meta-mafic rock — Rock derived from preexisting mafic rocks by essentially solid-state, mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Composed mostly of iron- and magnesium-bearing, dark-colored and (or) green minerals. Includes greenstone, amphibolite, and metagabbro.
• Meta-felsic and intermediate rock — Rock derived from preexisting felsic and intermediate-composition rocks by essentially solid-state, mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Composed mostly of light-colored minerals; relatively enriched in silica. Includes metagranite, metadiorite, and meta-andesite.
• Meta-volcaniclastic rock — Rock derived from preexisting volcaniclastic rocks by essentially solid-state, mineralogical, chemical, or structural changes, in response to marked changes in temperature, pressure, deformation, and (or) chemical environment, generally at depth in Earth’s crust. Composed of deformed but recognizable particles or clasts of volcanic explosive material.
• Other materials —
• Rock and sediment — Various rocks and sediment, not differentiated.
• Rock — Various rock types, not differentiated.
• “Made” or human-engineered land — Modern, unconsolidated material known to have human-related origin.
• Water or ice —
• Unmapped area —

GeoMaterialConfidence Terms

The appropriateness of a selected GeoMaterial term for characterizing a map unit is described by values in the GeoMaterialConfidence field, which provide the map user with a potentially useful qualifier term. Please refer to the “Scope and Intent” section (in the introductory material of this appendix) before assigning confidence values. Table 1–1 describes the terms (and their definitions) that populate the GeoMaterialConfidence field in a DescriptionOfMapUnits table.

Reference Cited in Appendix 1

Published and Unpublished Sources for Terms and Definitions (Modified as Needed) in the GeoMaterial Field, as Listed in Appendix 1