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Case 6
This is the case where fossils dating back to the first sedimentation phase are displayed. The bulk of the findings were obtained at the lignite mine of Santa Barbara. In the centre of the case there are some pieces of lignite and, to the two sides, some prehistoric leaves. The leaf fossilization developed through two separeted processes: when we find dark brown and almost black leaves it means that the originals had been transformed into a thin coal layer (fossilization through carbonization); if we find deep blue ones it means that the material which had formed the leaves was substituted by a mineral called vivianite (iron phosphate hydrate – Fe3+2(PO4)2*H2O). The findings of pine-cones are also very interesting. These fossils date back to the mid-Pliocene period (approximately 3 million years ago). Moreover, we must pay attention to the colour of the clay where leaves laid: it is grey and this implies that the environment where the clay had deposited was a marine and narrowing one. On the right side of the case, to the bottom, there is a mineral: it is an anapaite (a phosphate hydrate of calcium and iron – Ca,2Fe(PO04)2*2HO). As far as this substance is concerned, it is said to have a bizarre origin: the bones of dead and buried animals (mainly formed by phosphorus) deposited in lake sediments could have been melted by circulating water which, then, could have recrystalled phosphatus to produce anapaite. In this way, we can explain why animal fossils (that could have been melted) are so rare in the sediments that were deposited during the first lake phase. MORE>>
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