Some peculiarities of straight and zig-zag grain boundaries in multi-crystalline Si ingots were analyzed by Scanning Electron Microscopy-Electron BackScatter Diffraction (SEM-EBSD) and Three Dimensional (3D) grain boundary reconstruction. In the cases where straight grain boundaries were perpendicular to facing {111} planes in the two neighboring grains, they were found parallel, within the measurement accuracy, to the bisector of the two facing {111} planes. This is in agreement with the theory predicting the existence of Facetted-Facetted grooves during the growth of multicrystalline Si. Another grain boundary was corresponding to the predicted Facetted-Rough groove. It was found that the zig-zag grain boundaries were successively composed of {111} twin planes and ((4) over bar 11)/(01 1) planes, so that the two grains are always in Sigma 3 relationship. The phenomenon leading to the formation mechanism for these boundaries remains a subject for research. (C) 2014 Elsevier B.V. All rights reserved.