The rock fragment content (measured by log of polycrystalline/monocrystalline sand grains) of sand derived from five nearly identical granodiorite plutons, located in strongly contrasting climatic zones of the United States and Mexico, shows a much stronger correlation with source rock texture than with any environmental factor or combination of factors. These factors include mean annual temperature (range, −4° to 28°C), mean annual precipitation range (range, 201 to 1,566 mm), mean annual surplus of precipitation over evapotranspiration (range, 0 to 1,138 mm), average drainage slope (range, 0.29 to 0.61), or relief ratio (range, 0.17 to 0.70). Source rock texture is measured by intercrystalline area/volume of source rock and has a range of 7.99 to 25.08 mm⁻¹. Stepwise regression analysis indicates that, in coarse sand, 71% of variation in rock fragment content is accounted for by variations in source rock texture versus 16% accounted for by variations in temperature. In medium sand, 96% of the variation in rock fragment content can be attributed to texture versus 1% for slope and <1% for temperature. In fine sand, 92% of the variation in rock fragment content stems from texture versus 3% from temperature. The same analysis does not document a statistically significant relationship between precipitation and rock fragment abundance. Many previous studies that appear to document a relationship between rock fragment abundance and precipitation in modern and ancient sand have not accounted for variations in source rock lithology that are more plausible explanations for observed variations in rock fragment abundance in derived sand.