Title: Object of the Month - Flexible sandstone - Lapworth Museum of Geology
Duration: 1.44 mins
Speaker Names (if given): S1 Ashley, volunteer from Bishop Vesey grammar school
S1 Hi I’m Ashley, from Bishop Vesey’s in Sutton Coldfield and I’m volunteering here throughout the summer.
This may look like your bog standard piece of sandstone but actually, as you can see, it’s flexible.
It was found in Jhajjar, in India near Delhi, and has been lying here in the stores for a very long time.
The flexibility of these sandstones has puzzled geologists for many years and led to much discussion about why it’s so wobbly. Flexible sandstone was first discovered in the small area of Morro do Itacolomi in Brazil in 1822. It was thought to be a new type of rock, gaining it the name Itacolumite. Unfortunately it wasn’t a new rock and it was actually a sandstone formed from the decomposition of gneisses which contained feldspar grains.
This sediment accumulated together just like any old sandstone, but the feldspar grains continued to decompose. This would have left lots of empty spaces within the rock leaving it a lump of loosely interlocking grains of quartz. Where the quartz grains interlink with their neighbors, quartz crystals have grown creating joints, these are like your elbow or knee and allow the rock to manoeuvre like a wobble board. But in case you were wondering, the whole cliff or bed where this was lying wasn’t all wobbly, it’s only flexible when you cut it into thin sheets like this.
Platy minerals such as micas are sometime found in these sandstones but they don’t affect the flexibility. In some cases these sandstones are found to lose their flexibility as they dry out. So you better make the most of it while it’s still limber.
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