Argillite is a type of mudstone. For a classification of mudstone a chart is present in this section.

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 when the fissile layering typical of shale is developed. Argillite is commonly very deformed, fractured and veined. Although similar to shale, argillite is generally not fissile, i.e. does not preferentially break along closely spaced bedding planes. It differs from slate in its lack of foliation.

Characterization

Some factors on which it can be recognized:

• The texture is clastic.
• The clasts are not visible with the naked eye and smaller than 0.06 mm.
• It is a very hard rock.
• Its color varies from grey to black and can be green and red.
• Its clast compose of a mixture of clay minerals with any amount of quartz, feldspar and mica.
• It is smooth to touch.

References

• R. V. Dietrich, 2005, Gemrocks: Argillite Accessed Dec. 22, 2005.
• Museum of Civilization Haida argillite gallery 
• BC Govt MINFILE report, includes history and geological data.
• Dauzères, Alexandre, 2004, Ten Years of Argillite Study, Procedia Earth and Planetary Science
• USGS argillite