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Wackestone

Mud-supported carbonate rock that contains greater than 10% grains

Wikipedia contributorsAdapted for Fathomly · View authors
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Source updated April 21, 2026
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Under the Dunham classification (Dunham, 1962) system of limestones, a wackestone is defined as a mud-supported carbonate rock that contains greater than 10% grains. Most recently, this definition has been clarified as a carbonate-dominated rock in which the carbonate mud (<63 μm) component supports a fabric comprising 10% or more very fine-sand grade (63 μm) or larger grains but where less than 10% of the rock is formed of grains larger than sand grade (>2 mm).

01The identification of wackestone

A study of the adoption and use of carbonate classification systems by Lokier and Al Junaibi (2016) highlighted that the most common problem encountered when describing a wackestone is to incorrectly estimate the volume of 'grains' in the sample, in consequence, misidentifying wackestone as mudstone or vice versa. The original Dunham classification (1962) defined the matrix as clay and fine-silt size sediment <20 μm in diameter. This definition was redefined by Embry & Klovan (1971) to a grain size of less than or equal to 30 μm. Wright (1992) proposed a further increase to the upper limit for the matrix size in order to bring it into line with the upper limit for silt (62 μm).

A Wackestone in thin section (width of image is 10 mm)
A Wackestone in thin section (width of image is 10 mm)
Schematic wackestone as seen in thin section under the petrographic microscope. Type of carbonaceous rock according to the depositional texture: Alloctonous carbonates, Original components not bound at the deposition time. Less than 10% of components larger than sand size (> 2 mm) Contains carbonate mud (micrite, silt/clay size &lt;63 μm) Fabric supported by carbonate mud (micrite, &lt;63 μm) 10% or more composed of 63 μm or greater grains Legend: Dotted background: micritic matrix. Curved blue particles: bioclasts (indeterminate fossils, e.g. bivalve fragments). Blue cones: bioclasts (e.g. fossils of gastropods) Black spheroids: bioclasts (pellets).
Schematic wackestone as seen in thin section under the petrographic microscope. Type of carbonaceous rock according to the depositional texture: Alloctonous carbonates, Original components not bound at the deposition time. Less than 10% of components larger than sand size (> 2 mm) Contains carbonate mud (micrite, silt/clay size &lt;63 μm) Fabric supported by carbonate mud (micrite, &lt;63 μm) 10% or more composed of 63 μm or greater grains Legend: Dotted background: micritic matrix. Curved blue particles: bioclasts (indeterminate fossils, e.g. bivalve fragments). Blue cones: bioclasts (e.g. fossils of gastropods) Black spheroids: bioclasts (pellets).
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This article is adapted from the Wikipedia article “Wackestone”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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Greywacke or graywacke is a variety of sandstone generally characterized by its hardness (6-7 on Mohs scale), dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found in Paleozoic strata.