This is approximately 2,500 times as much Ar as is found in natural muscovite.

That is, a fresh mineral grain has its K-Ar "clock" set at zero.For example, in the Middle Proterozoic Musgrave Block (northern South Australia), a wide scatter of K-Ar mineral "ages" was found, ranging from 343Ma to 4493Ma due to inherited (excess) , permitting inclusion of the gas in the crystallizing minerals.Likewise, when Ar "dating" was attempted on Proterozoic granulite-facies rocks in the Fraser Range (western Australia) and Strangways Range (central Australia), it was found that garnet, sapphirine, and quartz contained excess was probably incorporated at the time of the formation of the minerals, and calculations suggested a partial pressure of ~0.1 atm Ar in the Proterozoic lower crust of Australia, which extends over half the continent.K–Ar dating is part of Wiki Project Geology, an attempt at creating a standardized, informative, comprehensive and easy-to-use geology resource.If you would like to participate, you can choose to edit this article, or visit the project page for more information.