Last week, my colleague and friend Thomas Taha kindly invited and escorted my family and me to explore the Natural History Museum in London. Walking through the Earth Galleries, my eyes were captured by an intruder in that section of the museum: in one of the portholes, containing rocks, I saw a “painting”. It seemed the artist had drawn a ruined cityscape.

But after a few seconds, reading the informations accompanying the “painting”, I realized my brain was suffering of a pareidolia. The painting was just a limestone rock. And the Artist was the Nature.

It was a rock called Pietra Paesina, a subgroup of the family of Pietra Alaberese.

The Pietra Alberese is a marly limestone belonging to the Ligurian series (Monte Morello Formation of Eocene age).

The Pietra Alberese has been widely utilized to build the town, because it is the only limestone cropping out in this part of Tuscany allowing the production of lime. In Prato and Pistoia, the Pietra Alberesewas also used as stone (e.g., ashlars) in the structures and façades of many public and religious buildings.

Cutting and polishing of the blocks of a subtypes PietraAlberese, known as Pietra Paesina, show the presence of a microcrystalline structure with grey/grey greenish to light blue colors (similarly to images of skies and bodies of water) in the inner part, whereas the external part is characterized by small polygonal to rectangular varicolored areas (generally yellowish to brown and locally to dark red, green and violet), similar to faulted millimetric bandings, such as to evoke landscapes with ruined houses, turreted castles, trees, canyons and peaks. These “drawings” are produced by the over millennial work of mineralized infiltrations in iron and manganese hydroxides.

Owing to this pattern, Pietra Paesina is also know as Ruin Marble.

Planning to have a magnificent and gigantic altar built, entirely inlaid with semiprecious stones, for the Medici Chapels (tomb of the Medici family), Ferdinand I commissioned the Dominican friar Agostino del Riccio to research and describe all the stones useful for this purpose that were available in the Grand Duchy of Tuscany, in order to have the greatest possible variety available.

Thus, it was that in his Istoria delle Pietre (History of Stones) of 1597 Agostino del Riccio cited particular stones collected in the Arno river bed: …In Arno assai frombole, et sassi, che hoggi di’ s’usano segare cosi’ poi lustrare, che in essi si veggono varie fantasie, et scherzi, che fa la Madre natura… (In the Arno there are many slings, and stones, which nowadays are used to saw so then to polish, that in them you can see various fantasies, and jokes, which Mother Nature makes)

The poet Pablo Neruda, an exile in Europe, lived for some time in Florence around the years 1950/51. He was so impressed by the images evoked by the Pietra Paesina that he wrote these poetic verses: