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Mineral Resources > Online Spatial Data > Geology > by state > Virginia Geology

Geologic units in Fairfax county, Virginia

[Additional scientific data in this geographic area]

Dalecarlia Instrusive Suite (Cambrian-Ordovician) at surface, covers < 0.1 % of this area

Dalecarlia Instrusive Suite - Monzogranite and granodiorite.

Lithology: monzonite; granodiorite

Mather Gorge Formation - Metagraywacke (Proterozoic Z-Cambrian) at surface, covers 4 % of this area

Mather Gorge Formation - Metargillite is metagraywacke

Lithology: meta-argillite

Newark Supergroup; Sandstone, undifferentiated (Upper Triassic) at surface, covers 6 % of this area

Sandstone, undifferentiated

Lithology: sandstone

Quaternary and Tertiary Deposits (Tertiary-Quaternary) at surface, covers 0.2 % of this area

Quaternary and Tertiary Deposits - Tabb through Windsor Formations and alluvial/tidal prism deposits.

Lithology: sand; gravel; silt; clay or mud; peat; alluvium

Shirley Formation (Quaternary) at surface, covers 5 % of this area

Shirley Formation - Interbedded gravel, sand, silt, clay, and peat; at altitudes to 35-45 ft. (top of unit).

Lithology: gravel; sand; silt; clay or mud; peat

Newark Supergroup; Triassic Sandstone, Siltstone, and Shale (Upper Triassic) at surface, covers 4 % of this area

Interbedded sandstone, siltstone, and shale

Lithology: sandstone; siltstone; shale

Falls Church Intrusive Suite (Cambrian-Ordovician) at surface, covers 2 % of this area

Falls Church Intrusive Suite - Tonalite, granodiorite, monzogranite, and trondhjemite.

Lithology: tonalite; granodiorite; granite; trondhjemite

Bacons Castle Formation (Tertiary) at surface, covers 1 % of this area

Bacons Castle Formation - Gravel grading upward into sand and sandy clayey silt

Lithology: gravel; sand; silt; clay or mud

Miocene Sand and Gravel (Tertiary) at surface, covers 1 % of this area

Miocene Sand and Gravel - Sandy gravel, sand, silt, and clay.

Lithology: gravel; sand; silt; clay or mud

Metagraywacke (Proterozoic) at surface, covers < 0.1 % of this area

Metagraywacke - Meta-argillite is metagraywacke, exotic blocks within melange units

Lithology: meta-argillite

Wissahickon Formation; Boulder Gneiss (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Wissahickon Formation; Boulder Gneiss - (Formerly mapped as Sykesville and Laurel Formations.) Thick-bedded to massive, pebble- and boulder-bearing, arenaceous to pelitic metamorphic rock; typically a medium-grained, garnet-oligoclase-mica-quartz gneiss; locally an intensely foliated gneiss or schist; apparent thickness 15,000 feet.

Lithology: gneiss; schist

Phyllite (Cambrian-Ordovician) at surface, covers < 0.1 % of this area

Phyllite.

Lithology: phyllite

Sykesville Formation (Cambrian) at surface, covers 7 % of this area

Sykesville Formation - Metasedimentary melange

Lithology: melange

Tabb Formation (Quaternary) at surface, covers < 0.1 % of this area

Tabb Formation - Undifferentiated. Includes the Poquoson Member (Qtp), Lynnhaven Member ( Qtl) and Sedgefield Member (Qts).

Lithology: sand; silt; peat

Piney Branch Complex (Proterozoic Z-Cambrian) at surface, covers 2 % of this area

Piney Branch Complex - Metamorphosed mafic and ultramafic rocks

Lithology: serpentinite; schist; plagiogranite

Popes Head Formation - Old Mill Branch Metasiltstone Member. Meta-argillite is metasiltstone (Cambrian-Ordovician) at surface, covers 6 % of this area

Popes Head Formation -Old Mill Branch Metasiltstone Member. Meta-argillite is metasiltstone

Lithology: meta-argillite

Windsor Formation (Tertiary-Quaternary) at surface, covers 0.3 % of this area

Windsor Formation - Interbedded gravel, sand, silt, and clay; at altitudes to 85-95 ft. (top of unit).

Lithology: gravel; sand; silt; clay or mud

Schist (Proterozoic) at surface, covers 0.2 % of this area

Schist as exotic blocks within melange units

Lithology: schist

Bear Island Granodiorite (Ordovician) at surface, covers < 0.1 % of this area

Bear Island Granodiorite - granodiorite

Lithology: granodiorite; pegmatite

Newark Supergroup; Triassic shale and siltstone (Triassic) at surface, covers 2 % of this area

Interbedded shale and siltstone

Lithology: shale; siltstone

Occoquan Granite (Cambrian-Ordovician) at surface, covers 10 % of this area

Occoquan Granite - Granite

Lithology: granite

Newark Supergroup; Conglomerate, mixed clasts (Upper Triassic) at surface, covers 2 % of this area

Conglomerate, mixed clasts

Lithology: conglomerate

Ultramafic Rocks (Proterozoic) at surface, covers 0.3 % of this area

Ultramafic rocks as exotic blocks within melange units

Lithology: ultramafitite (komatiite)

Pliocene Sand and Gravel (Tertiary) at surface, covers 3 % of this area

Pliocene Sand and Gravel - Sandy gravel, gravelly sand, poorly to well-sorted sands, and thin- to medium-beds of clay and silt, at altitudes from 170-320 ft. (top of unit).

Lithology: gravel; sand; clay or mud; silt

Wissahickon Formation (Undivided) (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Wissahickon Formation (Undivided) - Muscovite-chlorite-albite schist, muscovite-chlorite schist, chloritoid schist, and quartzite; intensely folded and cleaved.

Lithology: schist; quartzite

Popes Head Formation - Station Hills Phyllite Member. Phyllite. (Cambrian-Ordovician) at surface, covers 1 % of this area

Popes Head Formation - Station Hills Phyllite Member. Phyllite.

Lithology: phyllite

Chopawamsic Formation - Interlayered felsic and mafic metavolcanic rocks (Cambrian) at surface, covers 0.2 % of this area

Chopawamsic Formation- Interlayered felsic and mafic metavolcanic rocks

Lithology: metavolcanic rock

Annandale Group - Lake Barcroft Metasandstone (Proterozoic Z-Cambrian) at surface, covers 1 % of this area

Annandale Group - Lake Barcroft Metasandstone

Lithology: metasedimentary rock

Indian Run Formation (Cambrian) at surface, covers 2 % of this area

Indian Run Formation - Metasedimentary melange

Lithology: melange

Alluvium (Quaternary) at surface, covers 1 % of this area

Alluvium - Poorly sorted organic material, clay, sand, and rounded pebbles and cobbles

Lithology: alluvium; clay or mud; sand

Mather Gorge Formation -- Schist (Proterozoic Z-Cambrian) at surface, covers 19 % of this area

Mather Gorge Formation - Schist.

Lithology: schist; gneiss; metasedimentary rock; calc-silicate rock

Potomac Formation (Cretaceous) at surface, covers 9 % of this area

Potomac Formation - Pebbly, poorly sorted quartzo-feldspathic sand interbedded with sandy clay and silt; minor organic-rich clay and silt

Lithology: sand; clay or mud; silt

Yorkshire Formation (Cambrian) at surface, covers 0.2 % of this area

Yorkshire Formation - Polygenetic melange

Lithology: melange

Georgetown Intrusive Suite (Cambrian) at surface, covers 0.1 % of this area

Georgetown Intrusive Suite - Tonalite, quartz gabbro, quartz diorite, metapyroxenite, and hornblendite.

Lithology: tonalite; gabbro; greenstone; hornblendite

Metagabbro (Proterozoic) at surface, covers < 0.1 % of this area

Metagabbro

Lithology: metamorphic rock

Chuckatuck Formation (Quaternary) at surface, covers < 0.1 % of this area

Chuckatuck Formation - Interbedded gravel, sand, silt, clay, and minor peat; at altitudes to 50-60 ft. (top of unit).

Lithology: gravel; sand; silt; clay or mud; peat

Quantico Formation - Slate and porphyroblastic schist (Ordovician) at surface, covers 0.1 % of this area

Quantico Formation - Slate and porphyroblastic schist

Lithology: slate; schist

Diabase (Jurassic) at surface, covers 4 % of this area

Diabase

Lithology: diabase

Charles City Formation (Quaternary) at surface, covers 0.2 % of this area

Charles City Formation - Interbedded sand, silt, clay and minor gravel; at altitudes to 70-80 ft. (top of unit).

Lithology: sand; silt; clay or mud; gravel

Annandale Group - Accotink Schist (Proterozoic Z-Cambrian) at surface, covers 2 % of this area

Annandale Group - Accotink Schist.

Lithology: schist; meta-argillite