Our recent experiment showed that muons implanted into black phosphorus (the most stable allotrope of the element, with a low band gap of 0.3eV) are apparently diamagnetic, with full initial asymmetry but interesting relaxation behaviour. We plan to follow up this preliminary data with a more thorough study, to find if muonium states are also present - either a shallow donor at low temperature, or a rapidly charge-cycled state giving relaxation at higher temperature.