Dendrites from Germany

We’re planning to launch a collection of ‘images that look like plants but aren’t’, and this beautiful dendritic stone will certainly be amongst them. It arrived last week with several others from a German website – http://www.topgeo.de/ – and originates, like so many on the market, from the famous Solnhofen limestone, a fossil-rich Jurassic formation that lies between Nuremberg and Munich in Bavaria.
The plant-like branching patterns form through a process known as ‘Diffusion Limited Aggregation’: molecules of water-borne manganese move about randomly, and when they bump into each other, stick together. Repeated billions of times, various types of dendritic (‘leaf-like’, from the Greek) patterns emerge. These are amongst the most universal patterns in nature, at every scale from blood vessels to continental river drainage systems. There’s a book about them due out in September by the excellent science-writer, Philip Ball, the last of a trilogy based on his earlier book ‘The Self-made Tapestry’ – I’ve got that and the two that have already been published, ‘Shapes’ and ‘Flows’, and 'Branches' is a snip as a pre-publication buy on Amazon!

Laguna agate

Most of the agate images on the website are made from Brazilian material. Recently, however, I decided to venture into the more expensive world of collector-quality specimens, amongst which Mexican agates loom large. Most come from Chihuahua, the largest of Mexico’s thirty-one states and reputedly home of the eponymous, diminutive breed of dog. Mexican agates were first documented in 1895, but it wasn’t until some fifty years later that a few American collectors, travelling a newly constructed highway, found small agate nodules close to the road. They are now commercially mined and prized by collectors and jewellery makers worldwide.
With the exception of the celebrated Crazy Lace Agate, which is featured on the cover of the Formations book that is for sale on the website and forms in cracks of an older Cretaceous limestone, Mexican agates are found in volcanic rocks from 38 to 44 million years old. Each variety is named after a nearby ranch, hacienda, or – like the Laguna agate shown here – a railway station. Laguna agates are famed for their fine colour banding and the exquisitely delicate detail shown above is an enlargement of an area only 1cm (3/8”) wide. It was bought from the website Beautiful Agates and happily, given its tiny size, required minimal ‘cleaning’.