Itacolumite is a naturally occurring

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

that is flexible when cut into relatively thin slabs. It occurs at Itacolomi, its

eponym An eponym is a noun after which or for which someone or something is, or is believed to be, named. Adjectives derived from the word ''eponym'' include ''eponymous'' and ''eponymic''. Eponyms are commonly used for time periods, places, innovati ...

, in the southern portion of

Minas Gerais Minas Gerais () is one of the 27 federative units of Brazil, being the fourth largest state by area and the second largest in number of inhabitants with a population of 20,539,989 according to the 2022 Brazilian census, 2022 census. Located in ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. The stone is porous, and often yellow in color. It is also found in Kaliana village (

Charkhi Dadri district Charkhi Dadri District is one of the 22 districts of Haryana state in north west India near Rajasthan border, but not sharing border with Rajasthan. Created on 1 December 2016, the district headquarters is the city of Charkhi Dadri. History ...

, Haryana, India), the U.S. state of Georgia, and Stokes and McDowell counties of

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

. It is the best and most widely known example of a flexible sandstone, and is a source of diamonds found in the Minas Gerais area of Brazil. On the split faces of the slabs, scales of greenish

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

are visible, but in other respects, the rock seems to be a remarkably pure specimen consisting of quartz. If a slab measuring 30-60 centimetres long and few centimetres thick is cut and then placed so that it is supported at its ends only, it will gradually bend due to its own weight. If it is then turned over it will straighten and bend in the opposite direction. Flakes a millimetre or two thick can be bent between the fingers and are said to give out a creaking sound, but specimens showing this property form only a small part of the whole mass of the rock.

Cause of flexibility

Discussions have taken place regarding the exact cause of the material’s flexibility. At one time it was ascribed to the presence of thin scales of mica which were believed to permit a certain amount of motion between adjacent grains of

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

. More probably, however, it is due to the porous character of the rock together with the interlocking junctions between the individual quartz

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

grains. The porosity allows interstitial movement, while the hinge-like joints by which the particles are connected hold them together in spite of the displacement. These features are dependent to some extent on weathering, as the original rock matrix contained constituents which were later removed, leaving open cavities in their place, while at the same time additional

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

may have been deposited on the quartz grains, interlocking their irregular surfaces more perfectly together. Most of the known itacolumite specimens are also fine-grained. In some cases, they are said to lose their flexibility after being dried for some time, probably because of the hardening of the interstitial substance, but many specimens kept in a dry atmosphere for years retain this property to a high degree.

References

External links

Video of flexible itacolumite sandstone.
Retrieved 2014-02-04. {{Authority control Sedimentary rocks Sandstone