There's also a chance that diffuse axial (or pseudo-axial) lighting might turn out OK for a coin like this. Since it's in a slab, you'd need a special setup with really even lighting, so you could subtract out the uniform glare reflected from the slab.
However, it looks like this slab has hairlines, and the coin is dark, which makes axial lighting difficult.
However, it looks like this slab has hairlines, and the coin is dark, which makes axial lighting difficult.























