Itacolumite is a naturally occurring

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

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

eponym An eponym is a person, a place, or a thing after whom or which someone or something is, or is believed to be, named. The adjectives which are derived from the word eponym include ''eponymous'' and ''eponymic''. Usage of the word The term ''epon ...

, in the southern portion of

Minas Gerais Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. The stone is porous, and often yellow in color. It is also found in Kaliana village ( Charkhi Dadri district, Haryana, India), the

US state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sove ...

Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...

, and Stokes and McDowell counties of

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. 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 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

Discussion 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 atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

. 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 defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...

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 , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

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