Most fusions require dances, as it allows two gems to synchronize, as symbolised by the merging of dancing styles. There are few exceptions, such as Garnet's first fusion and Sardonyx's most recent fusion (however, Sardonyx did perform a hand based dance). This results in fusions lasting several seconds. However, in the episode Earthlings Part 2, both Smoky Quartz and the Jasper fusion both don't dance. (Nothing about that episode in particular, just those fusions.) Smoky's fusion may be explained by the synchronisation between Amethyst and Steven, and I've seen theories saying corrupted gems may not be able to resist fusion attempts. However, as you can see from the title of this post, I have another Idea.
When the Rubies fuse in The Answer and Hit the Diamond, they need merely be in position. This is because they are the exact same gem types. Perhaps this logic can be extended - If Jasper is correct about the corrupt gem's typing, then all fusions in the episode Earthlings involved quartz. It is possible the gem Jasper fused with was, in fact, a Jasper, as real-world Jaspers come in many colours and patterns. This exact same typing could be the explanation for the near-instantaneous fusion. Whether the fusion's instability was due to the gem's resistance, corruption difficulties or something else altogether is unknown to me.
Similarly, both Amethyst and Steven are quartz, which - when combined with their similar moods - may be the reasoning for Smoky's quick, and stable, fusion.
I also considered whether this may apply to Steven and Connie, due to their speedy, stable fusion in Crack the Whip against Jasper, as this required no dancing. However, I feel this is more easily attributed to the intricacies of Hybrid Fusion.
I bring this up as I want to know other's opinions, theories and thoughts on the matter. I also question whether or not these should be in the 'Same Gem Fusion' category, although I feel this should be saved for those of Exact same typing and level of corruption (e.g. If the corrupt gem was a Jasper, I wouldn't consider it a same gem fusion). Thank you for your time.