:''"Argillite" may also refer to Argillite, Kentucky.'' Graptoliitargilliit Pakri

Argillite () is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts of silt-sized particles. The argillites grade into

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

when the fissile layering typical of shale is developed. Another name for poorly lithified argillites is ''

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

''. These rocks, although variable in composition, are typically high in aluminium and silica with variable

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

and

alkaline earth The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are all s ...

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s. The term ''pelitic'' or ''pelite'' is often applied to these sediments and rocks. Metamorphism of argillites produces

slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...

, phyllite, and pelitic schist.

Belt Supergroup

The

Belt Supergroup The Belt Supergroup is an assemblage of primarily fine-grained sedimentary rocks and mafic intrusive rocks of late Precambrian (Mesoproterozoic) age. It is more than thick, covers an area of some 200,000 km2 (77,220 sq. mi), and is considered ...

, an assemblage of rocks of late

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

( Mesoproterozoic) age, includes thick sequences of argillite, as well as other metamorphosed or semi-metamorphosed mudstones.Schieber, J. 1990. Significance of styles of epicontinental shale sedimentation in the Belt basin, Mid-Proterozoic of Montana, U.S.A. Sedimentary Geology, v. 69, p. 297-312. It is exposed primarily in western Montana, including the

Bitterroot Valley The Bitterroot Valley is located in southwestern Montana, along the Bitterroot River between the Bitterroot Range and Sapphire Mountains, in the Northwestern United States. Geography The valley extends approximately from Lost Trail Pass in Id ...

and Bitterroot Mountains, the Missoula area,

Flathead Lake Flathead Lake ( fla, člq̓etkʷ, label=Salish, kut, yawuʔnik̓ ʔa·kuq̓nuk) is a large natural lake in northwest Montana. The lake is a remnant of the ancient, massive glacial dammed lake, Lake Missoula of the era of the last interglacial. ...

, and Glacier National Park, and in northern Idaho. There are also minor occurrences in northeastern Washington and western Wyoming. Excellent outcrops of deep purple, wine red, red, blue, turquoise, and green argillites of the Belt Supergroup can be seen in Glacier National Park in northwestern Montana and in Wolf Creek Canyon along Interstate 15 in west-central Montana.Alt, D.D. and Hyndman, D.W. 1986. Roadside geology of Montana. Mountain Press Publishing Co., Missoula, Montana, 427 p. .

"Black slate"

The Haida carvings of Haida Gwaii along the coast of British Columbia are notable aboriginal art treasures created from a type of a hard, fine black silt argillite, sometimes called "black

". The black slate occurs only at a quarry on a

Slatechuck Mountain Slatechuck Mountain, known as Kaagan in the Haida language, is a summit on south-central Graham Island in Haida Gwaii, formerly known as the Queen Charlotte Islands of the North Coast of British Columbia, Canada. It is located about 9 km wes ...

in the upper basin of

Slatechuck Creek Slatechuck Creek is a short but culturally important stream on Graham Island in the Queen Charlotte Islands of the North Coast of British Columbia, Canada. Only 6.7 km in length , it is located on the south flank of the small range including ...

, near the town of Skidegate on Graham Island. At one time, around 1900, it was shipped to Victoria for manufacturing; today the

Haida Haida may refer to: Places * Haida, an old name for Nový Bor * Haida Gwaii, meaning "Islands of the People", formerly called the Queen Charlotte Islands * Haida Islands, a different archipelago near Bella Bella, British Columbia Ships * , a 1 ...

have a monopoly on use of the argillite. Argillite carvings are synonymous with

artwork and are one of the few art forms on the Northwest Coast that is the exclusive right of one cultural group. This artwork has been of high quality and prized around the world since the Haida first began carving it to trade and sell to sailors around 1800. Contemporary Haida carvers continue the tradition.

References

R. V. Dietrich, 2005, ''Gemrocks: Argillite''
Accessed Dec. 22, 2005.

BC Govt MINFILE report
includes history and geological data. * Dauzères, Alexandre, 2004, Ten Years of Argillite Study, Procedia Earth and Planetary Science
USGS argillite
{{Authority control Sedimentary rocks de:Schiefer#Tonschiefer

Belt Supergroup

"Black slate"

See also

References