In September 2017 I wrote a short piece on lime swirls, more correctly known as the Ostwald Liesegang space super-saturation nucleation depletion cycle..:

I have now seen these in the UK, Southern Italy, Sicily, Corsica and now in Prague (Czech Republic) too.    There is very little known about them, except that they only seem to occur in mature putty limes that are rich in calcium or magnesium.

The swirls seen here date from about 1560.