PETROGRAPHIC DESCRIPTION

Clipsham Stones petrographic description

This is the description and classification of the Clipsham limestone


Macroscopic Examination – observations made by unaided eye

In hand specimen the stone is pale brown in colour and has a rough open texture with variable grain size. The constituents are generally poorly sorted, moderately compacted and consist principally of cemented peloids and bioclastic material of various types.

Microscopic examination – observations studied under a microscope

Composition

In thin section the principal constituents are peloids and bioclastic fragments, these being cemented and not generally clast supported. The degree of packing is variable but typically low with a low level of compaction visible with minimal grain distortion apparent.

The peloids are micritic in nature and typically 1 to 1.5mm in length/diameter. A number of different shell fragments are evident, with gastropods and bivalves being the most prevalent.

Cement

The clasts are well-cemented within a coarse sparitic calcite cement which shows two phases of formation. A finer-sized phase has formed around the periphery of the clastic grains with a coarser more blocky phase then forming within the interparticle void. Following staining with Alizarin Red S and potassium ferricyanide the cement has been identified as ferroan calcite.

Porosity

Porosity within the sample is variable up to 5% with the voidage being primarily intraparticle.

Classification

On the basis of this examination the stone can be classified as a poorly sorted, loosely compacted BIOPELSPARITE.

Building Research Establishment Ltd 2006

 

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