Here is white one

Nice!

I did some research and found that when the hollow space gets completely filled by solid agate or crystals it ceases to be a geode and is now called a nodule. So indeed a hollow space must be present to be called a geode.

Good point there, dave.
As Scott has now clarified for us that a "Geode" does indeed need a cavity or hole in the middle of it to qualify as such, one would assume that Geodes that don't have cavities are 'duds',
but that ain't necessarily so. 

daves64 wrote on Apr 14^th, 2022 at 12:18am:


I pulled this info from Wikipedia  -  "Geodes can form in any cavity, but the term is usually reserved for more or less rounded formations in igneous and sedimentary rocks." (https://en.wikipedia.org/wiki/Geode)

According to this it appears you can call any crystal lined cavity a geode. I know I may seem pedantic to keep trying to refining this, but I've always wondered specifically about this question. I have seen what looks exactly like a geode in the parent rock (no nodule) and had always felt that geode still described it. But as you know Wikipedia is not necessarily the definitive source of information so this could still be debatable.