SiO2 + Minerals
Shapes like Grapes
Botryoidal means ‘resembling grapes’ as derived from Greek for grape. It refers to Agate that grows in such a way that smooth, bulbous shapes are created. The growth can be large, you can see with the scale of my hand, as with this agate that fortified or started filling in a hollow.
The aggregates of the crystals may form in much smaller bunches like bubbles. These hot looking suds exhibit something of a bloom to the plume agate underneath that swirls around nearby visible in a cleaved off section.
Pearls in the Stone
Sometimes the culprit or impetus for the spherical shapes is apparent. A mineral may start the shape from within while crystals grow away from it fanning out from its center. It brings to mind the sand that starts the pearl in the Oyster.
The Botryoidal stones are typically beautiful on the outside with their smooth, fascinating surface. Many times there are equally interesting things going on inside. This Thunder Egg grew a dark blue botryoidal layer before starting linear fortification lines. Polishing into these gems is always an adventure into the unknown which is a great reason to do so.
Like with the Carnelian Botryoidal Plume Agate, this plume had lovely undulations before polishing. The rippling was repeated through the inside of the gem causing the white clouds in the clear agate to dance above the plumes.