We report on high-field terahertz transients with 0.9-mJ pulse energy produced in a 400 mm(2) partitioned organic crystal by optical rectification of a 30-mJ laser pulse centered at 1.25 mu m wavelength. The phase-locked single-cycle terahertz pulses cover the hard-to-access low-frequency range between 0.1 and 5 THz and carry peak fields of more than 42 MV/cm and 14 Tesla with the potential to reach over 80 MV/cm by choosing appropriate focusing optics. The scheme based on a Cr:Mg2SiO4 laser offers a high conversion efficiency of 3% using uncooled organic crystal. The collimated pump laser configuration provides excellent terahertz focusing conditions. (C) 2014 Optical Society of America