Looking For An Awe Inspiring Garden Feature? This Will Do Gneissly.
Post date: 30 Mar, 2022
After finding this eye-catching boulder in the CED Stone Landscape Scotland Depot's yard, we consulted our resident geologist Simon Copsey for a little more information on the interesting banding on the boulder which appeared to be raised on the outer surface of the stone.
Simon was happy to oblige and give us a little geology/history lesson. Enjoy....
This stone is a Gneiss which is a metamorphic stone meaning it has been changed by heat and pressure. Gneisses are the stones within the metamorphic family that have undergone the most transformation as they have been subjected to intense heat and pressure deep within the crust. The heat is so great that the stone semi melts (think toffee or warm plastic) and the pressure is so great that the various minerals in the stone separate and clump together into bands. This stone has pretty much just had vertical pressure as the banding is straight but it is possible for horizontal pressure to cause the stone to stretch and flow (see example below).
The brown colour in the banding is likely the oxidisation of natural iron minerals so this would have started life as a black and white banded Gneiss but it has oxidised over thousands of years.
This boulder is also glacial so during the last ice age this stone was ground out of a mountain and rolled along at the bottom of a glacier until the glacier has melted and the boulder was dumped and probably sat there until it was found by our boulder hunter.
Gneisses tend to be the oldest stones in fact the oldest rocks in the UK are Lewisian Gneisses up in the Isle of Lewis which are 3 - 1.7 billion years old, though I imagine that this one will be quiet a bit younger than these ones probably 500+ million years old.
To put that in context the dinosaurs were alive 252-65million years ago and complex life started about 540 million years.
Now that, is a feature stone!