Architectural Geology of Seville, Part 2: La Giralda and the Seville Cathedral Apse

Standing near the southern end of the Plaza del Triunfo and looking north-northwestward.

This was the first time I beheld this famously beautiful minaret-turned-belltower. It immediately reminded me of something, but I simply couldn't figure out what. Then, years later, I realized that I'd often stood next to a copy of it, on Chicago's Wrigley Building.

As with some of my other 1970s slides, this one had gone through some interesting color changes before I scanned it. So now it almost looks like a hand-painted postcard. Regardless, it still shows a remarkable amount of detail under magnification.

To wit: Giralda's individual bricks are visible, and they certainly demonstrate what the structure's main building material is. The tower's original form was designed by the Almohad-era architect Ahmad ibn Baso, and was fully functional by AD 1182.

So far I have not come across any technical discussions of the Giralda brick. It's reasonable to assume that it was produced locally, but confirmation of that is lacking.

In addition to using fired clay for both structural and dazzlingly ornamental effects, the builders were canny recyclers of stone materials. For one thing, the whole massive edifice stands on a foundation of ashlar blocks taken from both ancient Roman and Abbadid buildings. And the marble columns adorning the Giralda exterior were also spolia, and were appropriated from sources whose style is that of the Umayyad Caliphate.

I'm also happily surprised by what can still be seen on the Cathedral apse (eastern elevation) in the foreground. Individual blocks of ashlar are discernible, as is a considerable amount of the weathering effect known as black crusting. Here it's a bit purplish.

As noted in Part 1 of this set, Seville's great church is, geologically speaking, a gigantic agglomeration of many rock types acquired from more places than anyone now remembers. However, according to Bello and Martín 1992 (see my reference list in Part 1) the predominant variety seems to be a biocalcarenitic limestone, originally tinted pale yellow, quarried in El Puerto de Santa Maria. If I interpret the EGDI bedrock map correctly, this unit is Pliocene in age.

Unfortunately, the development of black crusts and biocalcarenites seem to go together. The process begins when partially combusted carbon particles produced by everything from burning wood to auto emissions and industrial pollution land on the Cathedral's stone. The carbon soot acts as a catalyst for a chemical reaction in which sulfate pollutants also present in the air transform the original carbonate mineral, calcite, into the sulfate mineral gypsum. And then more dark-tinted particulate matter lands on the gypsum and sticks to it.

The other photos and descriptions of this series can be found in my Architectural Geology of Seville album.

Taken in: Spain / Andalusia / Seville / Santa Cruz (show map)

Taken on: April 11, 1978

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architecture

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La Giralda

belltower

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Sets appears in: • Architectural Geology of Spain • Architectural Geology of Seville more » • The Beauty of Building Materials • Foundations & Substrates • Fuligology: The Science of Soot • Grab Bag of All Things Brick • Natural History: Spain • Sacred Places and Spaces • Urban Exposures: La città esaminata « less

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Camera: MAKER NAME 96660, ISO 50 (more info) (hide info)

Camera:	MAKER NAME 96660
ISO:	50
Flash:	Auto, Did not fire
Exposure Program:	Program AE
Metering Mode:	Average
White Balance:	Auto
Color Space:	Uncalibrated
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