Deposit oxidation

Laterites and a warm climate in the late Cretaceous and early Tertiary periods

The Chaillac barite deposit, from its formation to the Cretaceous, was under the sea and sedimentary cover (limestone and marl similar to the formations we cross on our way north to Chateauroux). At that time, conditions were reducing, and the colour of the ores was probably white, like that found under protective clay layers at the bottom of quarries close to the unconformity with the bedrock.

A hot, humid climate developed from the Cretaceous to the Eocene, leading to laterite-type solid alterations.

 

 

Laterites: the earth rusts, especially the sulfides, which transform into iron hydroxides and oxides. Locally, goethite accumulations are mined as iron ore.

At this point, goethite was formed and, along with pyromorphite, is one of Chaillac's signature minerals for collectors.

 

Goethite (FeO(OH))

Named after the poet and mineral collector Goethe.

Generally finely divided (it's the ochre used as a dye), it occurs in Chaillac in the form of beautiful acicular crystals. Goethite is transformed into hematite by dehydration (first few meters below ground surface) and the effect of temperature.