Kankar or Kunkur is a sedimentological term derived from Hindi, occasionally applied in India and the United States to detrital or residual rolled, often nodular calcium carbonate formed in soils of semi-arid regions. It forms sheets across alluvial plains and can occur as discontinuous lines of nodular kankar or as indurated layers in stratigraphic profiles more commonly referred to as calcrete, hardpan or duricrust .
This material was used extensively in India for major constructions. A typical example being the Curzon Bridge, Allahabad.
In the Report on the construction of this Bridge, kindly provided by the Institution of Civil Engineers, records as follows  :-
The Kunkur lime used on this bridge was burned under contract in a contiuous kiln, and ground in a disintegrator. The raw Kunkur was obtained partly from pits to the west of Phaphamau village and partly near Karchana; the former was found to be more reliable. When the Kunkur was dry and the kilns in good working order it took 14 cubic feet of coal dust to burn 100 cubic feet of Kunkur. 120 cubic feet of Kunkur of cleaned and broken raw Kunkur was found to give 100 cubic feet of lime.
- Wikipedia "Kankar"; Retrieved 5 May 2018
- Institution of Civil Engineers "The Curzon Bridge at Allahabad" by Robert Richard Gales, 1908, page 31; Retrieved 3 May 2018