Unfortunately, the dirt chunk doesn’t match the striations of normal dirt, and the grass won’t perfectly match the grass colour either (it seems to be set on the main grass colour from the lowest elevation)
Based on what @malley showed of the landmark system it’s quite possible to have a “natural dirt chunk” summon stone including striations, however I believe you’d need to have variants for the lowlands, plains and foothills grass colours (although only one for each elevation, the grass colours will match that used by the relevant elevation in each biome). There’s no intelligent “use the appropriate grass colour for the level it’s placed on” option from what I can see, rather, each of the elevations’ grass colour is its own entry and even when taking advantage of masking you can only mask to a particular level (i.e. “these blocks represent grass from the lowlands elevation”)
Another limitation is that summon stones won’t match the edge blending which occurs around elevation changes, since this is handled at map generation. [side note: I wonder if it would be possible to mod it so that the game re-calculated the edge blending once the game is running, either on a trigger or on a regular basis?]
At the moment, the easiest option would be to use the dirt chunks, and remove the single top layer to use grass patches to replicate the natural look. Unfortunately this will only pass on the lowest elevation for now; if we get variants for each elevation and the dirt chunks were modified to include the striations (something for ACE to handle? @SnorrLaxZ for visibility), then it would be much easier to do convincing terraforming.
Personally, I use the chunkier landmarks such as the geyser and the rune site to hide my failed terraforming experiments. The stone chunks have proven very useful to me since the mountains are much more forgiving when it comes to matching things up; but I’m lucky that all the things I wanted to patch up were on the bottom layers of the mountain – I suspect that the colours won’t match on the higher levels. I’ve given up on trying to change the shape of the grassy cliffs, or trying to undo the addition of the “flat stones” to an otherwise pristine grassy area (I’m just going to build over the damage… thankfully it’s what I was planning to use the area for anyway, I was hoping to pretty it up first to inform the building design but after seeing the result and trying to undo it that backfired horribly hahah.)
It’s a really cool feature, it’s just a huge shame that it couldn’t get more time in the oven – it definitely feels under-baked right now. Luckily we can fix that through modding in good time; but I’m worried that for a lot of players it’s going to turn the most-requested feature into a little bit of a let-down when they realise it’s not (YET) quite the perfect, intuitive, do-exactly-what-you-want-with-terrain system we imagined.
And for the record I 100% agree that single block summon stones would have been extremely useful. The patches are actually a bit more powerful and can fulfill that function with the right know-how, but single blocks would have been very intuitive, and would be a great way to level up a rookie geomancer too.