To determine the age of archaeological sediments using Optically Stimulated Luminescence (OSL), researchers extract coarse-grain quartz under strictly controlled conditions to prevent resetting the geological signal. Under dim red light, the raw sediment is first sieved to isolate grains between and micrometers. Subsequently, the isolated fraction is treated with hydrochloric acid () to dissolve carbonates, which could otherwise interfere with subsequent chemical treatments. Once the effervescence ceases, the sample is washed prior to being treated with hydrogen peroxide () to remove organic matter. Crucially, the remaining minerals are then subjected to a dense liquid separation using sodium polytungstate at a specific gravity of to float off potassium feldspars, which exhibit unwanted luminescence signals. Finally, the remaining heavy fraction is etched with concentrated hydrofluoric acid () for minutes. This etching serves a dual purpose: it dissolves any remaining feldspars and simultaneously etches away the alpha-irradiated outer shell of the quartz grains, leaving pure quartz cores ready for measurement.
Based on the passage, if a researcher omits the dense liquid separation step using sodium polytungstate, which of the following is the most likely consequence for the final quartz sample?
- The final quartz sample will remain contaminated with potassium feldspars, as the -minute hydrofluoric acid () etch is only intended to clear residual traces rather than the bulk of these minerals.Answer
- BThe initial sieving process will fail to isolate grains within the to micrometer range due to the presence of unseparated minerals.
- CThe hydrochloric acid treatment will fail to dissolve carbonates because the potassium feldspars will shield them from chemical reaction.
- DThe hydrogen peroxide treatment will react directly with potassium feldspars, preventing it from successfully removing organic matter.