Ever seen a piece of rock bend? Itacolumite is unique kind of sandstone that does when cut into thin strips. If a foot-long piece, a few centimeters thick, is supported at its ends it will gradually bend by its own weight. If it is then turned over it will straighten and bend in the opposite direction. Flakes a millimeter or two thick can be bent between the fingers and are said to give out a creaking sound.
The rock was first discovered in Mt. Itacolumi, hence named Itacolumite, in Minas Gerais, Brazil in 1822. It has since been found at a handful of places in India, France and the USA. However, the best samples still come from the Minas Gerais area.
Photo: St. Mary's University/Flickr
At one time it was believed that the flexibility of itacolumite was due to the presence of thin scales of mica which acted as lubricants allowing motion between adjacent grains of quartz. However, more recent research suggest the flexibility is due to the presence of intergranular void spaces among the irregular quartz grains, together with the interlocking junctions between the sand grains. The voids allow interstitial movement, while the hinge-like joints by which the particles are connected hold them together in spite of the displacement. The voids may have been created due to weathering when perishable constituents within the sandstone got leached away leaving open cavities in their place, while at the same time additional silica may have been deposited on the quartz grains fitting their irregular surfaces more perfectly together.
In some cases, itacolumite loses their flexibility when dried, probably because of the hardening of some interstitial substance, but many specimens kept in a dry atmosphere for years retain this property in a high degree.
While there is no direct application of itacolumite yet, researchers believe that understanding this rock and its interlocking pattern can help in building ductile ceramic material and earthquake resistance building materials.
Photo: madskittlesbro/Imgur
References:
# Pawan Kumar et al, Itacolumite (Flexible Sandstone) From Kaliana, Charkhi Dadri District, Haryana, India, Journal of the Geological Society of India
# Wikipedia
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