Do we know what the rigid mantle looks like? The rigid mantle, which is hard and lies above the asthenosphere, is separated from the "crust" that we can see and touch by the Mohorovičić discontinuity. Wikipedia provides an image of what may once have been part of the discontinuity, but I haven't been able to find a good source on what the actual rigid mantle looks like.

Do we know what the rigid mantle itself looks like or how it would look to the naked eye? That is, if I could somehow use my Unobtainium 9000 SuperDrill to drill down to the mantle and excavate a 1 meter squared cube of rigid mantle, what would it actually look like once I got it up to the surface? Would it just look like a slab of random silicates like as could be found in some mine today? Would it look distinctly "alien"?
Above the asthenosphere is the lithosphere. The main constituent of the lower lithosphere is peridotite, a coarse-grained igneous rock containing the minerals olivine and pyroxene. Samples of peridotite can be found in the surface. Sections of ocean crust can be uplifted onto continental margins, forming ophiolites (perhaps the best-known example being the Troodos Ophiolite). They are also found as fragments in basalts and kimberlites, the vertical intrusions that often contain diamonds. So there are lots of places on the surface where you can go and see what the upper mantle looks like! But in the meantime, a closeup of a peridotite is shown below.