L310 - Breccia

L310 hand specimen. Note por sorting of clasts.

L310 thin section, plane-polarised light. Note angular clast shapes.

L310 thin section, cross-polarised light. Note clast support.

Specimen Age

Permian

Location

Brockram, Cumbria

Hand Specimen

Very poorly sorted.Angular to sub-angular clasts up to 30 mm long. Randomly orientated.
Clasts mainly pale grey, some white, some red.
Red-brown colour of the fine-grained matrix indicates iron staining.
Matrix and some clasts fizz with acid, indicating that they are made of carbonate. This is a limestone.

Thin-section

Variety of clasts: sedimentary rock fragments, carbonate and feldspar crystals, fine-grained quartz and carbonate, some bioclasts. Clasts are quite angular.
Matrix of very fine-grained clays containing fragments of quartz and carbonate.

Rock History

Clast-supported. Clasts are angular, so sediments cannot have been transported far. (NB, if this rock were matrix supported the clasts could have been transported a long way without losing their angularity.)
Probably scree accumulation during desert conditions, from approximately the same horizon as L326.

Advanced Notes

Iron-staining
Hematite(Fe₂O₃) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH₂O) → yellow or brown iron-staining

The red-brown colour of this rock is probably produced by hematite.

Rock Name

breccia