Argillaceous minerals may appear silvery upon optical reflection and are minerals containing substantial amounts of clay-like components (Greek: ἄργιλλος = clay). Argillaceous components are fine-grained (less than 2 µm) aluminosilicates, and more particularly clay minerals such as kaolinite, montmorillonite-smectite, illite, and chlorite. Claystone and shales are thus predominantly argillaceous.
The adjective "argillaceous" is also used to define rocks in which clay minerals are a secondary but significant component. For example, argillaceous limestones are limestones consisting predominantly of calcium carbonate, but including 10-40% of clay minerals: such limestones, when soft, are often called marls. Similarly, argillaceous sandstones are sandstones consisting primarily of quartz grains, with the interstitial spaces filled with clay minerals.
This article does not cite any sources. (January 2008) (Learn how and when to remove this template message)
|This article related to petrology is a stub. You can help Wikipedia by expanding it.|