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Oriostoma

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Before preparation

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After preparation

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Before preparation

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After preparation

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The island of Gotland is known worldwide for its rich fossil deposits from the Silurian Period. Besides trilobites, corals, brachiopods, cephalopods and crinoids, a whole series of very beautiful gastropods can be found. These are usually extremely well preserved, but are sometimes difficult to free from its surrounding marl or limestone. A chemical preparation with e.g. Rewoquat can sometimes achieve very good results, but often bears the risk that parts of the fossil are blown off. In addition, it is only effective on marly matrix. Limestone matrix won’t be dissolved.¬†

In this case, very good results can often be achieved with fine blasting. These snails of the genus Oriostoma were exposed under the microscope with very fine air abrasives. One species exhibits very high and thin ribbed arches that are spine or sail-like in extension. Such structures can only be preserved during preparation with special care. The second species has a special feature: In the mouth still lies the operculum, which could close the shell. In addition, a small bryozoan colony has settled on the shell.

Fossils: Oriostoma sp.

Locality: Gotland (Sweden)

Formation: Silurian, Wenlock, Klinteberg Formation

Width of the snails: 3 and 4 cm

Work required: about 3 hours each