Browse Items (264 total)

Hand Specimen Very fine-grained rock with a prominent, well-developed cleavage. The dark red-purple colour is due to iron-staining. The light green smudge is a reduction spot. Thin-section Mud size grains.Mainly indistinguishable clay…

Hand Specimen Two rock types, with an irregular contact between them. 1 – Very dark brown, microcrystalline rock. This fizzes with acid. It is a limestone. 2 – Grey and black, intermingled, microcrystalline silica. Brittle and well jointed. Some…

Hand Specimen This rock is made up of cryptocrystalline silica (quartz), black to brown. Being made up of silica, it is hard and displays conchoidal fracture. This is a flint nodule, which comes from a chalk bed – notice the thin shell of white…

Hand Specimen This rock is made up of light grey sub-spherical ooids. Fine to medium sand grain size. A few lithic/biogenic fragments. Dark grey cement. Small hair-line white veins run through this rock. Thin-section Ooids made up of a greenish…

Hand Specimen This rock is made up of well cemented bioclasts. The bioclasts (mainly shell fragments) are poorly sorted, ranging from <1mm up to a few 10s of mm. Fine-grained cement fizzes with acid, indicating that it is carbonate. It has…

Hand Specimen Grey-buff colour rock made up of ooids, mainly medium grained and spherical. Some shell and lithic fragments. Well compacted and cemented by calcite, which fizzes with acid. Thin-section The ooids look brown. They are made up of…

Hand Specimen Pale buff coloured, crystalline rock. Numerous cavities, thought to have been formed by shrinkage during alteration of primary calcite (CaCO3) to secondary dolomite (CaMg[CO3]2). There is a weak reaction to dilute acid, which…

Hand Specimen This white rock is virtually pure carbonate. It fizzes with acid. It is fine-grained and poorly cemented, making it soft and low density. It is commonly known as ‘chalk’. Thin-section Very uniform cryptocrystalline carbonate. Rare…

Hand Specimen 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…

Hand Specimen 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…