Coral

Fossil

Single Coral free of limestone, partial, from the Burren, County.Clare

In general the organisms with the greatest fossilisation potential, are those with a hard external skeleton, small size and a lifestyle which involves living in an area where sediment is accumulating.

One of the primary uses of fossils is in dating rocks, a study known as biostratigraphy. This is possible because the organisms that formed the fossils evolved over time. After an organism is buried, the second stage begins – that of transforming it into a fossil. Physical stresses have an effect – most plant fossils are preserved and flattened impressions because the originals have been crushed by the weight of the rock over them.

Most organisms that are preserved in shales and clays are crushed by the extreme compaction of these rocks after burial. The aragonite of an ammonite shell can be dissolved and replaced by sediment or by another mineral such as pyrite. Iridescent aragonite is unstable, and over millions of years, will convert to a stable equivalent, calcite, as featured on the Brachiopod exhibit.

Clays or complex mineral assemblages frequently replace organic fossils, such as leaves.

Ref: 2000.26

Geology Collection
National Museum of Ireland, Earth Science Division Collection