Very uniform cryptocrystalline carbonate.
Rare larger calcite crystals <0.5mm.
Very uniform cryptocrystalline carbonate.
Rare larger calcite crystals <0.5mm.
Pale yellow-grey mudstone containing the fossil remains of a small arthropod with a segmented exoskeleton.
The rock is banded and shows some surface discolouration due to weathering.
Rock fizzes with acid, so contains carbonate.
This is a soft, though well consolidated limestone (the surface has been scratched).
Moving across the slide, perpendicular to the laminations, there are alternations (gradual transitions) between calcareous mudstone and argillaceous limestone. One band is rich in angular quartz grains (0.1 to 0.2 mm), and contains carbonate shell fragments.
Calcite mudstone – fine-grained mosaic of calcite, small proportion of transparent brown impurity and a few small grains of quartz.
Argillaceous limestone – even finer grained calcite mosaic, more abundant brown material (probably organic) than in the calcite mudstone.
Jurassic
Purbeck
Near Salisbury
Pale yellow-grey mudstone containing the fossil remains of a small arthropod with a segmented exoskeleton.
The rock is banded and shows some surface discolouration due to weathering.
Rock fizzes with acid, so contains carbonate.
This is a soft, though well consolidated limestone (the surface has been scratched).
Moving across the slide, perpendicular to the laminations, there are alternations (gradual transitions) between calcareous mudstone and argillaceous limestone. One band is rich in angular quartz grains (0.1 to 0.2 mm), and contains carbonate shell fragments.
Calcite mudstone – fine-grained mosaic of calcite, small proportion of transparent brown impurity and a few small grains of quartz.
Argillaceous limestone – even finer grained calcite mosaic, more abundant brown material (probably organic) than in the calcite mudstone.
Very dark grey to black mudstone.
Faint, fine-scale laminations visible on cut surface.
Not fissile - does not readily split along bedding planes.
Contains fossils and fossil imprints.
Some glinting flakes of mica.
This rock fizzes gently with acid, indicating that it contains some carbonate.
Weathered to light brown-grey in places.
Fine-grained, so formed in a very low energy environment.
Shells are too large to have been swept in by such low energy currents, so the shells are in life position.
If the shells are indeed gastropods and bivalves the rock could be marine or non-marine. The presence of brachiopods would indicate a marine environment.
Lower Carboniferous
Millstone Grit Series
Bowland, West Yorkshire
Very dark grey to black mudstone.
Faint, fine-scale laminations visible on cut surface.
Not fissile - does not readily split along bedding planes.
Contains fossils and fossil imprints.
Some glinting flakes of mica.
This rock fizzes gently with acid, indicating that it contains some carbonate.
Weathered to light brown-grey in places.
Fine-grained, so formed in a very low energy environment.
Shells are too large to have been swept in by such low energy currents, so the shells are in life position.
If the shells are indeed gastropods and bivalves the rock could be marine or non-marine. The presence of brachiopods would indicate a marine environment.