“Liesegang banding” in sandstone from the Upper Paleozoic of Tennessee, USA.

Irregular, reddish or brownish or orangish-brown iron oxide banding is commonly seen in many porous rocks, particularly sandstones and pebbly sandstones. These have been almost universally referred to as “Liesegang banding”, representing precipitation lines of iron-rich minerals (e.g., hematite, limonite, goethite, etc.) at & along groundwater chemical interfaces. But, according to Neil Wells of Kent State University, the original concept of Liesegang banding (Liesegang, 1896) does not match up with what is seen in the rock record (see Wells et al., 2003).

True Liesegang banding refers to parallel bands of precipitate formed by diffusion along a single chemical gradient during one event. What's seen in the rock record often consists of sets of irregularly concentric iron bands, with different sets of bands quite frequently oriented in different directions, and showing cross-cutting and dissolution of older sets. Iron banding in the rock record is clearly the result of numerous precipitation events over long periods of time by moving groundwater (Wells et al., 2003). Iron mineralization along these bands appears to be induced by the presence of either a redox interface (change from reducing to oxidizing conditions in the groundwater) or a pH interface (change in acidity).

Because Neil Wells is the first (apparently) to point out that what geologists have been calling Liesegang banding really isn’t, a renaming seems to be in order. It was jokingly suggested in 2003 that the iron banding discussed above be called “Wells Banding”. I’m all for that.

From Diemer et al. (2012) - Building Stone Walking Tour of Uptown Charlotte:

The 1.5 acre urban pocket park known as the Green is located between the 400 block of South Tryon and South College Streets, immediately west of the Charlotte Convention Center. Designed by Wagner Murray Architects of Charlotte, it was completed in 2002 and sits directly on top of a 7-level underground parking structure.

Sandstone blocks in the retaining wall

This fine-grained quartz sandstone was quarried near Crossville, Tennessee. Red iron staining highlights cross-bedding on some specimens. The high quartz content of this sandstone, deposited along the coast of an inland sea that covered most of North America in the Mississippian, about 340 million years ago, has made it a desirable and durable building stone. It is called a fieldstone because it has been left in its natural state.

Provenance: quarry near Crossville, Cumberland County, east-central Tennessee, USA

Locality: building stone in wall at "The Green", College Street & 2nd Street, downtown Charlotte, North Carolina, USA

References:

Liesegang, R.E. 1896. Ueber einige Eigenschaften von Gal-lerten [On some properties of gelatin]. Naturwissenschaftliche Wochenschrift 11: 353-362. (see also: Liesegang, R.E. 1945. Geologische Bänderungen durch Diffusion und Kapillarität [Geologic banding by diffusion and capillarity]. Chemie der Erde, Zeitschrift der Chemischen, Mineralogie, Petrographie, Geologie und Bodenkunde 15: 420-423.)