Protuberance is a funny word that means a thing that protrudes or “sticks out” from something else. For small meteoroids, 90% of the mass is lost to ablation as they comes through the Earth’s atmosphere. If a stony meteoroid had a protuberance in space, the protuberance would be the first thing to break off or ablate away as the meteoroid passes through Earth’s atmosphere.

If you have a rock with a protuberance or other features that sticks out in positive relief, then it is not a meteorite.

Botryoidal hematite often has protuberances.

Pebbles conglomerates are sedimentary rocks in which, usually, the rounded pebble clasts are harder than the matrix. Except for the reddish one on the lower left, the the whitish clast are largely quartz, a very hard mineral.

All of these rocks have features that stand out in “positive relief.” The 3 rocks at the top are some kind of concretions, I don’t know how these form, but they must be common because I’ve been sent several photos like this.