Agate, Jasper, Geodes, & Thundereggs

Here you'll find all manner of Quartz based minerals in their various forms.
What's the difference between Agate and Jasper? While they're both formed of similar materials (microcrystalline Quartz/Chalcedony), Agate tends to be semi-translucent, while Jasper is opaque. This isn't a 100% rule but is a common way to tell them apart. Because of their similar structure, they can even form together.

Geodes differ from Thundereggs in that Geodes have larger hollow cavities lined with small crystals, while Thundereggs typically have solid centers or only very small voids.