  A dodecagonal quasicrystal showing 12-fold symmetry forms in Mn-rich
quaternary alloys containing 5.5 or 7.5 at.% Cr, 5.0 at.% Ni and 17.5 at.% Si.
After annealing at 700 C for 130 h, the quasicrystal precipitated in a matrix
of \b{eta}-Mn type crystalline phase. The shape of the quasicrystal is
needle-like having a length of several tens of micrometers. Electron
diffraction as well as powder X-ray diffraction experiments have revealed the
following characteristics of the quasicrystal; diffraction symmetry 12/mmm,
presence of systematic extinction for h1h2h2h1h5 type reflections with odd h5
index, and then five-dimensional space group P126/mmc. Indexing of the
reflections indicated that the dimension of the common edge in the equilateral
triangle-square tiling is 4.560 {\AA}, and the periodicity is 4.626 {\AA} along
the 12-fold axis. This is the first example of the dodecagonal quasicrystal
synthesized by ordinary metallurgical method in 3-d transition-metal alloys.
