Well that was a surprise. Nice subject, thanks Mr Shuko. Here we go with a

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MINERAL

objectithing for your ongoing delight.

[Boolbar] Earthly? YES.
[Software] Metallic? NO, not essentially.
[Rosie] Artificial? NO.
[Raak] NO. But a very good guess.

[Rosie] NO, not a celestial object
[Raak] NO, see above
[Superman] YES, it's down under
[Tuj] YES, there can be only one.

Yup, that was easy enough. Ayers Rock did finish a little-known Australian SF story called The Mountain Movers by being revealed as a stone space ship. Nevertheless Rosie gets there first and will take this boomerang-shaped baton for the next round. Well done!

Talking of boomerangs, I made one in 1974 from instructions in the New Scientist, which explained the aerodynamics. I've still got it; it's probably under a pile of junk in the garage somewhere. It really works but you need an area the size of a football pitch and preferably no wind. Boomerangs are chiral, i.e. -handed and mine, to suit, is a southpaw. Having said all that, it's now deduction time.

The next object, which has but the most tenuous link with steam engines, is:

VEGETABLE and MINERAL

Is it a potato iron?