re: Blueberries are not anyone's balls...
That the ones found so far have been of a a single mineral and not basalt or some other basic rock would seem to proves they are not tektite or similar ejecta created forms.
Which are invariable a form of glass composed of the imapcting meteorite and native materials. Besides they wouldn't cool quick enough in Mars’ thin atmosphere to be the nearly spherical shapes they appear to be either.