A new indium(III) silicate, K2In(OH)(Si4O10), has been synthesized by a high-temperature, high-pressure hydrothermal method. It crystallizes in the monoclinic space group P2(1)/m (No. 11) with a = 11.410(1) Angstrom, b = 8.373(1) Angstrom, c = 11.611 (1) Angstrom, beta = 112.201(2)degrees, and Z = 4. The structure, which is analogous to that of K2CuSi4O10, consists of unbranched vierer 4-fold chains of corner-sharing SiO4 tetrahedra running along the b axis linked together via corner sharing by chains of trans-corner-sharing InO4(OH)2 octahedra to form a 3-D framework which delimits 8-ring and 6-ring channels to accommodate K+ cations. The presence of hydroxyl groups is confirmed by IR spectroscopy. The Si-29 MAS NMR exhibits four resonances at -88.6, -90.1, -97.4, and -98.2 ppm corresponding to four distinct crystallographic Si sites. A H-1 --> Si-29 CP/MAS NMR experiment was performed to assign the four resonances.