Sharply-facetted decahedral and icosahedral crystals of Ag were grown from vapor phase by evaporating Ag2O in the evaporation temperature range from 800 to 1000 degrees C. They are found resulting from conformal growth of smaller nuclei in which a compact structure out of tetrahedral units has already established-tiny decahedral and icosahedral crystals can be much smaller than 100 nm in dimension. The intrinsic stress, derived from the misfit angle of the assembled cyclic decahedron or a spherical icosahedron from the five or twenty tetrahedra, plays an important role to the corresponding growth mechanism. Different arrangements of twin boundaries in the decahedral and icosahedral nuclei define their morphology evolution. Uneven alignment of twin boundaries will divert the crystal morphology from regular (truncated) decahedrons and icosahedrons. These results demonstrate an effective route for the study of general mechanisms concerning the growth of twin crystals of noble metals. (C) 2011 Elsevier B.V. All rights reserved.