Dictionary:Z/A

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The ratio of atomic number Z to atomic weight A and, hence, proportional to the ratio of electron density (as measured by the density log) to mass density. Apparent density equals true density where Z/A=1/2, which is closely approximated for many minerals (e.g., quartz, calcite, anhydrite, dolomite). The apparent density is larger than the true density when Z/A>1/2 (e.g., gypsum, oil, 110% for water), smaller when Z/A<1/2 (e.g., salt).