Average density was carbon steel, impact speed was about 10 km/s which is pretty fair for a de-orbited colony coming from a Lagrange point on a direct course with little to no atmospheric braking outside of impact. The colony dimensions i mentioned were my initial estimate and the wiki's larher measurement.
For comparison you are not exactly right with the Chicxulub analogy, It released far more energy than the colony drop somewhere around 1.3x1024 J to 5.8x1025 J, it was an extinction level event that likely had knock on effects tectonic wise, likewise estimated size ranges 10.6 km to 80.9 km, so hypothetically it could very well have been within the size of colony, or likewise colonies could very well be within the size of it. Ill give you it had more mass, but i never claimed it was worse than Chicxulub. From (https://arxiv.org/ftp/arxiv/papers/1403/1403.6391.pdf
) Just that it would suck for a decade or so before things got anywhere near back to normal.
I think this was the reason they changed it to splitting in three to lesson the impact in the Origin, if it had happened like in the original in one whole piece it would have fucked the Earth for at least ten years. Jaburo would have been fine but living on the surface would suck, not to mention the drops done by operation stardust Neo Zeon and Char the Earth should already be nearly uninhabitable for the billions who still live there even without Axis.