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.
Mainly medium sand (to coarse sand in the case of L327a).
Yellow-brown iron stained quartz, cemented by the same yellow brown oxide. A few larger quartz grains up to 5 mm long. Grains are angular to sub-rounded, and poorly sorted.
Fizzing with acid, indicating that there is a carbonate cement.
Angular to sub-angular grains of quartz, displaying undulose extinction.
Most have thin brown rims of iron oxide.
A few grains of feldspar.
Minor carbonate cement (sparite).
Deposited in an aqueous environment, since it is not clean enough to be aeolian.
Iron staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The yellow colour of this rock is probably produced by limonite.
Cretaceous
Carston, Lower Greensand
Hunstanton
Mainly medium sand (to coarse sand in the case of L327a).
Yellow-brown iron stained quartz, cemented by the same yellow brown oxide. A few larger quartz grains up to 5 mm long. Grains are angular to sub-rounded, and poorly sorted.
Fizzing with acid, indicating that there is a carbonate cement.
Angular to sub-angular grains of quartz, displaying undulose extinction.
Most have thin brown rims of iron oxide.
A few grains of feldspar.
Minor carbonate cement (sparite).
Deposited in an aqueous environment, since it is not clean enough to be aeolian.
Iron staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The yellow colour of this rock is probably produced by limonite.
Quartz grains, sub-angular to sub-rounded, occasionally rounded, displaying undulose extinction.
Lithic fragments including flint and quartzite.
Some grains of feldspar.
Rare small green clasts.
Grain supported.
Cemented by a sparry calcite cement. The cement crystals are large, each enclosing a number of sedimentary grains.
Deposited in an aqueous environment; grains are not rounded enough to have been deposited in an aeolian environment.
The rare green clasts are made up of a cryptocrystalline material, which may be a type of amphibole called glauconite, and some rather decomposed rhyolite or andesite.
Quartz grains, sub-angular to sub-rounded, occasionally rounded, displaying undulose extinction.
Lithic fragments including flint and quartzite.
Some grains of feldspar.
Rare small green clasts.
Grain supported.
Cemented by a sparry calcite cement. The cement crystals are large, each enclosing a number of sedimentary grains.
Deposited in an aqueous environment; grains are not rounded enough to have been deposited in an aeolian environment.
The rare green clasts are made up of a cryptocrystalline material, which may be a type of amphibole called glauconite, and some rather decomposed rhyolite or andesite.
Quartz (~65%)
- Includes fresh quartz grains with undulose extinction, quartzite grains with internal sutures, and quartz vein material. Some quartz grains have opaque rims.
Feldspar (~35%)
- Mainly microcline, some plagioclase. Some microperthite texture and decomposition to clays.
All grains are moderately rounded and fairly well sorted. The rock is well compacted. A thin film of cement mainly hematite and clay coats the grains.
This rock contains too much feldspar, and the grains are not sufficiently well rounded nor well sorted to have been deposited in an aeolian environment. The sediments were deposited in an aqueous environment.
sandstone
feldspathic arenite
Quartz (~65%)
- Includes fresh quartz grains with undulose extinction, quartzite grains with internal sutures, and quartz vein material. Some quartz grains have opaque rims.
Feldspar (~35%)
- Mainly microcline, some plagioclase. Some microperthite texture and decomposition to clays.
All grains are moderately rounded and fairly well sorted. The rock is well compacted. A thin film of cement mainly hematite and clay coats the grains.
This rock contains too much feldspar, and the grains are not sufficiently well rounded nor well sorted to have been deposited in an aeolian environment. The sediments were deposited in an aqueous environment.
sandstone
feldspathic arenite
This rock was deposited in a moderate energy, aqueous environment. The grains are not well rounded enough to be aeolian sediments.
sandstone
arenite
This rock was deposited in a moderate energy, aqueous environment. The grains are not well rounded enough to be aeolian sediments.
sandstone
arenite