What constitutes a variety as in Grossular var. Hessonite?

Can someone please explain why this seemingly arbitrary distincion is made? I can find no information on Google -- other than that the Hessonite garnet is the Jyotish gem related to Rahu (Moon's ascending node ), which is mainly an elemental and instinctual entity ...

OK, I think I'm okay now.

Anyway, the hessonite page on MinDat gives no details other than a picture. Wiki, offers nothing; RUFF doesn't have an entry.

TIA/John

Hessonite is a name for gemmy garnet, particularly grossular (the orange to yellowish material). It is commonly used in the gem trade, and frequently misused by novice collectors (i.e. labeling an opaque grossular 'hessonite').

Best to avoid such useless varietal names.

Yeah, I'd agree--but mindat itself makes a point of listing it--but then doesn't give the basis for making the distinction...