Ocher rock
What is an ocher ?
Ocher is a ferric rock composed of pure clay colored by a pigment of mineral origin. This colored clay is amalgamated with the grains of sand , the ochers are found in the soil in the form of ocher sands composed of more than 80% quartz.
Where can we find it ?
Rock with this pigment of mineral origin which gives it a variety of color, charcoal black, red ocher and yellow ocher, the famous ocher quarry in Roussillon, Vaucluse more precisely '' South of France '', this is not the only deposit, there is another in Rustrel , Drôme, Gard and Nièvre in Bourgogne.
What does it used for ?
Ocher was used by man in painting with its various colors, and although ochers can be heated to intensify their colors , the Romans were a good users of this natural pigment that's why it is found in the walls of their buildings and castles and also in religious art and today it is like a colored paint for the surfaces of houses.
Clay ocher rock
In the eye of a sedimentologist, some researchers thought that these dunes of ocher formed by the wind are therefore of a continental origin, but the geologist Pr. Jean-Marie TRIAT (Geologist at the University of Marseille) approved that they are of marine origin; We can see in some cliffs deposits with an oblique or intercrossed stratification ; This is typical of the marine sedimentation which takes place in the continental shelf with a very low bathymetry ( 0 - 40 m ) and these are the marine currents and even the tidal currents , the flow, the reflux which classify the grains of sand, it was crumbly rock at the time , so definitely it's a marine sedimentation, there's also an other indic to say that it is , which is fossils traces and not any fossil trace ,the fossils which identify the type of fossils that only lives in the sea , traces of burial, that means that an animal that lives on the bottom of the sea are generally annelids (small worms) that cross the sediment looking for food, it is typical of the continental shelf that we don't have a large slice of water .
- About 140 Million year and during a million years, the sediments will be deposited at the bottom of the sea at the site of future Provence, it formed a thick layer of a limestone, and the rivers that are thrown into this sea will also entail quantities of sediments, clays then sands, here in this stage the rocks will be colored, when the microorganisms that live in the water die they deposit and mixed with the sand, these microorganisms will provide carbonate and organic matter, then with the contact of the high seas and the depth of about 40 m and less, these different components will combine together and form glauconia, a mineral that will color the sand in green .
To finish this story, about 80 million years, the earth or the provence will emerge and drag to the surface that green sand with an oblique stratification and traces of burial and small crystals of green glauconia , these sands formed after 80 million year will turn red to yellow , but why ? That's because the sand contains quartz and glauconia and if we see the glauconia in closest it is also made up of iron and silicon and aluminum, this combination it is originally green in color, when 80 million year ago the land was going to emerge ,provence was near the tropic of cancer, that means an extremely humid climate and under the effect of the falling rains glauconia will dissolve, silicon and aluminum will assemble to form kaolinite a white colored clay and when it assembles with oxygen and hydrogen (H2O) it will form glautite of the color varies red or yellow , so we can find the ocher in a different lands appearing like a red lands .
Are there another red lands?
Yes , there is laterite which is a rock that is formed all over the world in tropical areas, in South America, Africa , Asia and wherever we are near equatorial zones, the lands which are formed by kaolinite and glautite is the equivalent of ocher .
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