SW21 - Micaceous siltstone with plant debris
Click the microscope button to view a thin section for this sample.
Click the microscope button to view a thin section for this sample.

Fact sheet

SW21 - Micaceous siltstone with plant debris

A micaceous Carboniferous siltstone collected from Doulton's Claypit.

This siltstone was deposited in a low-lying, deltaic environment when the region lay near the equator. These deltas were thickly forested with trees whose fossil remains can be found in some of the strata; this siltstone had black organic fossil debris visible in outcrop on bedding planes.

In thin section, there is considerable, rather irregular variation in grainsize, with lenses of finer material suggesting that sedimentary layering runs roughly parallel to the long axis of the thin section. Grains include clear quartz, dusty feldspar, green chlorite, rarer mica laths, opaque oxides and lithic fragments, many of them appearing of mafic origin. Grains are generally rounded to subangular.

Possible candidates for the organic debris so conspicuous in hand specimen could be a couple of very elongate, irregular opaque grains towards the base of the main fine-grained layer, near the centre of the section. These may correspond to flattened plant debris.

Pale brown interstitial material is likely fine grained clays, while patches of interstitial pale green chlorite are abundant. A carbonate vein cuts obliquely across the lower left corner of the section, identifiable by the high interference colours under crossed polars. The two adjacent brown patches with clear centres to the right of centre in the image are some kind of surface contamination, perhaps spilled oil, not part of the rock.

This sample was collected as part of the 'Macro to Micro' project.

Additional images
  • Hand specimen of siltstone on black background
52.481429, -2.097206
Exposures on west side of Doulton's Claypit
About this collection

This Collection showcases the geodiversity of a classic geological site: the Saltwells National Nature Reserve in the West Midlands.

As well as displaying thin section and hand specimen views along with information setting them in the context of their landscapes, we also include perspectives and creative responses to the geological heritage of the sites from the local community.

Explore the stories of the rock layers at Saltwells and Wren's Nest NNRs, designed by students at King Edward VI School, Stourbridge:

This Collection was made possible by funding awarded to the 'Macro to Micro' project by the Natural Environment Research Council (NERC) under their 'Growing Roots' scheme.

Sample details

Collection: Saltwells
Rock-forming mineral
Accessory minerals
Category guide  
Category Guide
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Refers to any word or phrase that appears anywhere in the descriptions of the specimens
Accessory minerals
Minerals that occur in very low abundance in a rock. They are usually not visible with the naked eye and contribute perhapssver, they often dominate the rare elements such as platinum group metals.
Rock-forming minerals
Minerals that make up the bulk of all rock samples and are also the ones used in rock classi?cation.
Selecting one or more period, for example 'Jurassic'.
A term used to group together related samples that are not already gathered into a single Collection. For instance, there is a ‘SW England granites’ theme that includes such rock types as granite, hydrothermal breccia, skarn and vein samples.
A general term used to label a rock sample. It is a useful way of grouping similar samples throughout a collection. Category names are often, but not exclusively, common rock names (e.g. granite, basalt, dolerite, gabbro, greisen, skarn, gneiss, amphibolite, limestone, sandstone).
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We would like to thank the following for the use of this sample: