The Harvard 98973 Muscovite is a Li-rich muscovite from the mineral collection of the Mineralogical Museum, Harvard University, Cambridge, MA. It was recovered from a granitic pegmatite in the Lord Hill Quarry, Stoneham, Oxford Co., Maine, USA, is commercially available via IAGEO Ltd., serves as a reference material for light elements and is described in more detail elsewhere. It has not yet been directly dated; however, for the regional pegmatite field ages between 250 and 270 Ma are envisaged.