The density and porosity of lunar rocks

Accurate lunar rock densities are necessary for constructing gravity models of the Moon's crust and lithosphere. Most Apollo‐era density measurements have errors of 2–5% or more and few include porosity measurements. We report new density and porosity measurements using the bead method and helium pycnometry for 6 Apollo samples and 7 lunar meteorites, with typical grain density uncertainties of 10–30 kg m −3 (0.3–0.9%) and porosity uncertainties of 1–3%. Comparison between igneous grain densities and normative mineral densities show that these uncertainties are realistic and that the helium fully penetrates the pore space. Basalt grain densities are a strong function of composition, varying over at least 3270 kg m −3 (high aluminum basalt) to 3460 kg m −3 (high titanium basalt). Feldspathic highland crust has a bulk density of 2200–2600 kg m −3 and porosity of 10–20%. Impact basin ejecta has a bulk density of 2350–2600 kg m −3 and porosity of ∼20%.