A hundred million years ago, today's Mediterranean didn't exist. Continental bits and pieces that would become Spain, Italy, France, and the whole geological jigsaw that we see today jostled around in balmy tropical seas at the western end of the great Tethyan ocean that separated Africa from Asia. This ocean would later be consigned to the geological graveyard of the Alpine Mountain system, but, during much of the Jurassic and the Cretaceous periods, things were relatively peaceful. Tropical seas are limestone factories, and sometimes, wandering around the Alps, you can't help but wonder whether anything other than the carbonate cycle was going on -seemingly endless landscapes of limestone, now twisted and exhumed, dominate the scenery, as in the hills in the background of the photo above. But what's that in the foreground? Clearly something else was going on - rivers, coasts, and dunes were accumulating sands that would provide a brilliantly colourful relief from the gray limestone hills.
The brilliance of the palette of these sandstones in Provence, at the southern end of the exposed Alps, is the product of the alchemy of geochemistry and mineralogy, and this is one of the largest deposits of ochre in the world. The sandstones contained iron-rich clays between the sand grains and the conspiracy of time and water moving through the sands changed those minerals into a variety of other clay minerals, many with not only exotic names but also exotic hues. This is the area of the Luberon, around the hilltop village of Roussillon (distinct from the region of Roussillon to the south where I'm currently enjoying warm March sunshine). Ochre has been quarried there for millenia, and, at its peak towards the end of the nineteenth century, seventeen different tints were extracted and exported worldwide. The area became known as the "Colorado Provençal" (colorado being one of the Spanish words for red, hence the US state) and today you can walk any number of trails amongst the old quarries and the outcrops of ever-varying colours - purples, yellows, browns, reds and oranges.
The French geological description of these sandstones refers to their originally containing the green mineral glauconite, a complex hydrous silicate of iron that commonly contains a range of other ingredients - aluminium, magnesium, calcium, and so on. It was the glauconite that got caught up in the alchemy and changed into a variety of iron-dominated rusty minerals, goethite, hematite, limonite. Each of those rust minerals has a different colour, but the spectrum is also influenced by the size of the grains and their differing ways of interplaying with light. The sandstone, as can be seen in the photos above, display a variety of sedimentary structures, including dramatic cross-bedding, suggestive of rivers and dunes. Now glauconite is a mineral that is generally regarded as forming in the calm waters of shallow seas, but these sandstones do not have the appearance of having been deposited in such tranquil environments - was the glauconite perhaps eroded out of other (marine) sandstones and transported along with all the other detritus that ended up as the sands of the Colorado Provencal?
Ochre has long been used as a pigment, mixed with natural oils, both for prehistoric art and body ornamentation; it was used by ancient Egyptian women as rouge and lip gloss, and the ancient Picts (and "Red Indians"?) coloured themselves with blood-red ochre. Ochre dyes were used to preserve the canvas sails of English fishing vessels, and it may have contributed to the processes of treating hides. Ochre has been used lavishly in burials from cultures all over the world, and it would seem that this may reflect practical, as well as symbolic, properties. It was used by the Egyptians in the mummification process and in two thousand year old burials in North America; it is used today by native Australians to heal wounds and burns. Ochre would seem to be natural antiseptic.
And, of course, ochre is still used as a painting ingredient today. Visit the dazzling landscapes of the Colorado Provençal, and you can buy sets of natural pigments. Look in art supply catalogs and you'll find endless varieties of ochre colours. The alchemy of geochemistry and mineralogy is wonderful - no wonder Andrew Clemens could find all the coloured sand grains that he needed (see my Jan 9 post).
You might enjoy Victoria Finlay's book on Color and where we get pigments: http://www.amazon.com/Color-Natural-History-Victoria-Finlay/dp/0812971426/ref=sr_1_2?ie=UTF8&s=books&qid=1239045053&sr=1-2 . I had to skim the book, which strays far into her travelogue and away from the topic in places, but much of it is fascinating.
Posted by: Steve Gough | April 06, 2009 at 08:15 PM