Tuesday 28 March 2023

Flint Nodules

Richard Osgood and his team found an ovoid stone in their recent dig at Boles Barrow.

Photo with permission Richard Osgood

There has been some speculation as to what it might be. Rob Ixer kindly notes and supplied a photo of a fossil echinoid which is very similar, he writes:

"Photographs of the round-looking flint found recently a Boles Barrow show it has the shape and look of an echinoid, more specifically an echinocorys echinoid. These are a well-known and common fossils found in the Upper Cretaceous chalk of southern England, although not as abundant as irregularly-shaped flints associated with fossil sponges. 

They are uncommon (uncommonly recorded) finds within archaeological contexts and some have been confused with ‘marbles’, etc, especially if the rather insignificant ambulacra seen on echincorys are poorly preserved. Were the flint object to be an echinoid from the local chalk then it as not travelled far. 

The chalk also is the source of another misidentified material, namely rounded mammilated marcasite nodules. Many are brought into museums (almost as often as glass and metal working slags) and said to be meteorites, there is always a fiery tale. The correct identification leads inevitably to disbelief followed by disappointment of the finder. The find of a “natural pyrite meteorite” in a prehistoric shaman’s hut Bolkow Poland (the bedrock here is Cretaceous chalk)) being a prime example. Pyrite and marcasite haven’t been reported from meteorites the iron sulphide mineral is always troilite. 

Hence this flint requires a careful inspection by a Mesozoic specialist before further speculation. I doubt this will be the find of the century."

So a fossil echinoid is very likely, a natural flint nodule quite likely and a river pebble brought onto site as a hammer stone a possibility but it appears to lack percussion marks. Other suggestions such as a stone curlew egg can be dismissed.

Some of the flint nodules in my cabinet.

As an experiment I asked bard.google.com to write the rest of this post.

Flint nodules form when silica, which is a component of quartz, precipitates out of a solution and replaces the chalk. The silica comes from the skeletons of tiny sponges and siliceous planktonic micro-organisms (diatoms, radiolarians) that lived in the late Cretaceous period (60-95 million years ago).

The process begins with the silica-rich skeletons of these organisms dissolving in the seawater. This leaves a solution of silica in the water. At a shallow depth beneath the seafloor, the chemical conditions are right for the silica to form into flint, which literally replaces the chalk, creating nodules of flint of odd shapes and sizes and sometimes in continuous layers.

Flint nodules can be found in many parts of the world, including Europe, Asia, and North America. They are often used to make tools and weapons, as they are very hard and can be easily sharpened. 

Fossil echinoids These fossils are commonly known as thunderstones, fairy loaves, or shepherds' crowns. 

Fossil echinoids are not archaeological, but they can be found in archaeological sites. They are formed when a sea urchin dies and its hard shell is buried in sediment. Over time, the sediment hardens into rock, and the urchin's shell is preserved as a fossil.

Fossil echinoids can be found in many parts of the world, including Europe, Asia, and North America. They are often used to study the evolution of sea urchins and to understand the ancient environments in which they lived.

There are a few cases where fossil echinoids have been found in archaeological sites. For example, in 2016, a team of archaeologists found a fossil echinoid with an Anglo-Saxon inscription on it in London. The inscription was interpreted as a religious symbol, and the discovery suggests that early Christians may have used echinoids as religious objects.

However, fossil echinoids are not typically considered to be archaeological artifacts. They are more commonly seen as geological objects that can provide insights into the ancient world.

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