Grape Agate, is not actually agate at all, it is botryoidal purple chalcedony.  The name refers to the habit (crystal growth pattern) and color resembling bunches of grapes.

If you check out enough of my collection, you will notice many specimens chemically are SiO2 but look nothing alike, because it's complicated :-)

It almost all comes from ONE location in Indonesia. The trade name became famous after 2016 when miners discovered deposits in Mamuju Area, Sulawesi (formerly West Sulawesi), Indonesia, before that, the mineral was virtually unknown to collectors anywhere.

The purple color is caused by trace manganese or iron, exact chromophores vary by piece, but generally Mn²⁺ gives the purple, Ni or Fe can give green or blue tones.

Its color is stable (doesn’t fade like some blue halite or barite).