Late Quaternary geyserites in the Ol'khon area, Baikal rift zone, are a geologically and petrolog ically unique rocks, which may provide information on the character of hydrothermal processes during the development of modern rift zones. The geyserites of this area are characterized by the presence of minerals atypical of such rocks: highly crystalline graphite (which is usually formed at high temperatures) and α car byne (which is a natural carbon modification that has been previously found only among products of exper iments). Other newly formed minerals of the geyserites are equilibrium chalcedony, talc, and tremolite. This suggests that the rocks were formed under conditions significantly different from those under which classic geyserites are produced. Geyserites in the Ol'khon area were most probably produced by silica saturated solutions rich in certain ore components (Fe, Mn, Sb, As, and Y) and heated to temperatures of about 400°C.