This has a diameter of circa. Darkfield illumination enhances its internal structure. The blue colour is thought to be due to the inclusion of Ferroan Calcite, indicating an anaerobic environment. The black and brown mottled area is believed to be due to microcrystals of Pyrites, another indication of anaerobic conditions. Crinoids are a small species of the Echinodermata and are found also in remote times in limestones of the Carboniferous period.
Darkfield illumination used with stained cellulose lacquer peels shows many interesting aspects.
It often tends to increase the contrast in the images and can help to distinguish between dark wood fusain and pyrities, which so often occur together. Here we have two minute parts of an unstained lacquer peel, observed under XPL, to show optical figures of calcareous nannofossils embedded in transparent kerogen and other organic residues. The peel is from the Upper Jurassic, Upper Kimmeridge Clay, Freshwater Steps Stone Band. Freshwater Steps, west of Hounstout Cliff, Dorset coast. 120 microns X 80 microns and ca.