A systematic study of bone mineralogy in IIIrd Millennium BC burials sites from southwest Spain has shown that soil pH play an important role in bone preservation. In acidic soils, the hydroxyapatite of the bone become unstable and is partially dissolved and replaced by clay minerals (mainly vermiculite and halloysite).
As a result, the bone get an earthy texture and its frailty increase considerably, allowing a poor preservation.
On the other hand, in alkaline soils hydroxyapatite is partially replaced by calcite, increasing thetoughness of the bone and therefore favouring a better preservation. The behaviour of bones during these mjneralogical changes as an open system may hamper their use for geochronologicai determinations