Exerpt from chapter 13 (by JDA Clarke) of "Australian regolith studies" (Pain & Scott, in prep.)<br /><br />"The corrosive atmosphere and high temperatures and pressures suggest that chemical weathering may be significant on Venus (McGill et al. 1983). Furthermore, the reactions are often reversible over the temperature ranges experienced between the highest and lowest elevations of the planet. These reactions resemble more closely terrestrial thermal metamorphic processes than they do weathering. Examples include:<br /><br />* Wollastonite + CO2 << />> calcite + quartz<br /><br />* Forsterite + CO2 << />> magnesite + enstatite<br /><br />* 2 forsterite + diposide + 2CO2 << />> 2 dolomite + 4 enstatite<br /><br />* Calcite + enstatite + CO2 << />> 2 dolomite + quartz <br /><br />Traces gases in the atmosphere of Venus include water, hydrogen chloride, and hydrogen fluoride. The following reactions may occur if they are present in significant quantities:<br /><br />* 2 diopside + 3 enstatite + quartz + H2O << />> tremolite + 2 oxygen<br /><br />* 2 anorthite + 5 enstatite + quartz + H2O << />> tremolite + 2 andalusite<br /><br />* Orthoclase + 2 enstatite + 2 HF << />> phlogopite + 3 quartz + H2O<br /><br />* 2 albite + 2HCl << />> 2 halite + andalusite + 5 quartz + H2O<br /><br />Despite this, images from four locations on the surface of Venus (Veneras 9, 10, 13, & 14) show apparently unweathered surfaces. Whether this is because weathering proceeds more slowly than expected, or the four sites are fortuitously on young surfaces, or because the weathering do not produce mesoscopic degradation features familiar to terrestrial scientists, is not clear. However, the presence of loose regolith in most of the images shows that some weathering and fragmentation is occurring even at these sites.<br /><br />Measured wind velocities on Venus are low, less than 2m/s. These are, however, sufficient to move <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em> Arthur Clarke</p> </div>