The name “grape agate” has stuck as a marketing term. However, the name is a misnomer. Misnomers are names that are scientifically incorrect. There are no arguments with “grape” because of its purple color. But, the use of “agate” as a species/variety name draws objections. Here is an analysis…

Grape Agate: This name is inappropriate because agate should have parallel internal banding. The name agate also implies quartz with a microcrystalline texture; however, most of the grapes have a drusy surface – making them megascopically crystalline.

Grape Chalcedony: Like agate, the name chalcedony implies quartz with a microcrystalline texture.

Grape Quartz: The name quartz fits better than both agate and chalcedony. But, the appropriate name for purple quartz is amethyst.

Botryoidal Amethyst: The name “amethyst” better honors mineralogical and gemological definitions, and the adjective “botryoidal” communicates a rounded shape.

So, this author concludes that the name “botryoidal amethyst” is a name that is scientifically correct, but is not as much fun as “grape agate”.