Hi FIl,
I think this file shows what you were asking. I created a second circle that is the exact diameter of the gem, to have it be end to end like in your first example. If you use the larger one, there will be space between the gems. With the larger circle in the original sample file, I also created a duplicate circle there. So if you want to select both of those circles and run the ArrayGem Command on them, you can see the 2d objects created with a "0 spacing" set.
Here's what it looks like when I used your "larger circle" as the size pick for the ArrayGem Command. (I also Arrayed the circle to show how it is sizing it along the path.)
Just a note - you may possibly run into problems with ArrayGem if you have a large sized object and a path that has tight bends that make it squiggle around a lot in between where each item should be placed.
The method that is used to converge on a solution can possibly get sort of stuck in one of the squiggles in cases like that.
So for ArrayGem your path curve should try to kind of generally resemble the placement of the items and not have a bunch of extra little wiggles and bends in it that are much tighter than the bounding size.