Formation process of minerals in the bones

Minerals formed during diagenesis

In general, pyrite (FeS₂) is formed when the sediments’ ferrous iron (Fe²⁺) comes into contact with hydrogen sulphide (H₂S). It plays an important role in biology. In a fresh water environment, it is mainly produced through the deterioration of the sulphur compounds during the decomposition of the organic matter by sulphur bacteria. In a marine environment, it essentially results from the bacterial reduction of sulphates [SO₄^2-]. The reaction of the iron with the hydrogen sulphide produces an initial compound, an iron sulphide (FeS), which leads to pyrite when it reacts again with H₂S or with elemental sulphur. Several generations of pyrite have been identified.

Right at the beginning of diagenesis, the iron resulting from the decomposition of the haemoglobin and the sulphur resulting from the hydrolysis of the proteins can react and precipitate to form a first generation of pyrite (endogenous pyrite) that will settle within the Haversian canals and in the micro spaces resulting from the decomposition of the bone cells. This reaction takes place in a continental non-marine environment, as was the case at Bernissart at the beginning of the Cretaceous. Reconstitutions of the environment at the time are based on the various fossils found in the clay at Bernissart, and thanks to palynology, it has been possible to date the clay as being 125 million years old.

The second most important mineral formed during diagenesis is baryte [Ba(SO₄)]. This mineral precipitates out of fluids containing barium (Ba) in anaerobic sediments rich in organic matter. It forms after pyrite during the permineralization phase.

Minerals formed after the excavation of the Iguanodons

By comparing samples from 1878 with those from core drilling in 2002 that hadn't been subject to 130 years in the open air, it was possible to differentiate between the phenomena linked to diagenesis and those linked to exposure to oxygen and to variable temperatures and levels of relative humidity.

The principal minerals formed by the oxidization of the pyrite upon contact with the ambient air and humidity are hydrous iron sulphates, of which szomolnokite (FeSO₄.H₂O) and rozenite (FeSO₄.4H₂O) are by far the most abundant. This oxidization of the pyrite releases acids that, by disintegrating the Weald clay that has infiltrated or stuck to the bones, can induce the formation of other more complex sulphate minerals.

Gypsum [Ca(SO₄).2H₂O] is the result of the reaction of the calcium, arising from the dissolving of the bone apatite by these very acids, with the sulphates from the oxidization of the pyrite.