Definition

Noun: A sedimentary rock composed primarily of clay minerals and fine-grained silt particles. Argillaceous rocks are formed by the compaction and cementation of clay deposits over geological time.

Usage

Argillaceous rock is a technical term used in geology and earth sciences to classify a major category of sedimentary rocks. It is used to describe the rock's composition and origin.

Examples

• Noun:
  • Shale is a common type of argillaceous rock.
  • The canyon walls were composed of layered argillaceous rock, indicating an ancient lake bed.
  • Geologists analyzed the argillaceous rock sample to determine its mineral content.

Advanced Usage

• As a modifier: The term can function attributively to describe other geological features.
  • The region contains significant argillaceous rock formations.
• In scientific classification: Used to distinguish rocks based on composition (e.g., argillaceous vs. arenaceous [sandy] or calcareous [limy] rocks).

Variants and Related Words

• Argillaceous (adj): Of the nature of or containing clay.
  • The soil had an argillaceous quality, making it dense and sticky when wet.
• Argillite (n): A compact, dense argillaceous rock that has undergone a greater degree of induration than shale.
• Pelite (n): A general term for clay-rich sedimentary rocks; often used synonymously in geological contexts.

Synonyms

• Claystone (n): A fine-grained sedimentary rock composed mainly of clay-sized particles.
• Mudrock (n): A broader term encompassing all fine-grained sedimentary rocks like siltstone, mudstone, claystone, and shale.

Notes on Meaning

The term specifically denotes the rock's lithified state. The unconsolidated, pre-rock material is simply called clay or mud. The defining characteristic is a high content of clay minerals, such as kaolinite or illite.

Noun

1. a sedimentary rock formed from clay deposits