title: Rubidium-strontium chronology and chemistry of lunar material.
abstract: Igneous lunar rocks divide into two chemical types, probably representing two rock units. They form separate close groups on the isochron diagram; no total rock age is valid unless the rocks are cogenetic. Mineral isochrons prove that one type has an age of 3.80 +/-0.11 billion years, equal to the line joining total-rock groups, and the initial ratio of strontium-87 to strontium-86 of both types is close to 0.6994. Soil and breccias chemically resemble a mixture of the two igneous types, with a superimposed variation of mineral components, plus a small transferred component rich in nickel, copper, zinc, and possibly stron-tium-87.
authors.forename: W
authors.initials: W
authors.lastname: Compston
authors.forename: P A
authors.initials: PA
authors.lastname: Arriens
authors.forename: M J
authors.initials: MJ
authors.lastname: Vernon
authors.forename: B W
authors.initials: BW
authors.lastname: Chappell