Conglomerate rock

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Conglomerate is a coarse-grained rock, composed of rounded or angular rock fragments cemented together.

Sedimentary: Rounded or angular rock fragments cemented together (therefore technically a 'clastic sedimentary' rock).

Source location: Westland.

Sizes: Choose from dropdown menu either Shelf specimen (300–800g), or Hand specimen (less than 300g)

Note: Images are examples of specimens only. Sizes and shapes will vary.

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Conglomerate is a sedimentary rock characterised by its coarse-grained structure, composed of rounded or angular rock fragments cemented together by a matrix of finer-grained material.


Clastic sedimentary.

Physical properties of conglomerate

  • Colour: Exhibits a range of colours, including grey, brown, red, or yellow, depending on the composition of the rock fragments and cementing material.
  • Luster: Varies depending on the mineral content, but it is commonly described as dull or earthy.
  • Hardness: Variable hardness depending on the composition of the rock fragments, ranging from relatively soft to moderately hard.
  • Density: Varies depending on the composition and compaction, typically ranging from 2.2 to 2.8 grams per cubic centimetre.

General properties of conglomerate

  • Composition: Consists of a mixture of different rock fragments, such as pebbles, cobbles, or boulders, embedded in a matrix of finer-grained sediment or cement.
  • Texture: Characterised by its clastic nature, with distinct rock fragments visible within the rock.
  • Grain Size: A coarse-grained texture due to the presence of larger rock fragments.
  • Depositional Environment: Typically forms in high-energy environments, such as riverbeds, alluvial fans, or near the base of mountains.
  • Stratification: Often exhibits distinct layers or beds, reflecting changes in sedimentation and deposition over time.

Uses of conglomerate in New Zealand and worldwide

  • Construction: Used as a construction material, particularly for decorative purposes in building facades, walls, and landscaping.
  • Aggregate: Crushed conglomerate is used as aggregate in construction, including for road bases, concrete, and drainage systems.
  • Riprap: Large pieces are used for erosion control and stabilisation along riverbanks, shorelines, and slopes.
  • Geological Studies: Provides valuable information for geological studies, such as interpreting past environments, sediment transport, and depositional processes.
  • Fossils: Can contain fossil remains of plants, animals, or other organisms, offering insights into ancient ecosystems and paleoenvironments.