Geode or Agate?

[Jinx]

Anyone know the difference between these two rocks? I've never been able to discern a difference when (a) seeing pictures in rock books nor (b) seeing these in shops with other polished gems. To me, agate always comes as slices - resembling cross sections from geodes. Is this correct, or are they two distinctly different things?

[Harmonious Discord]

Agate

Lake Supperior Agate (Not cut)

Lake Supperior Agate Cut

Geode

Geode Again

You can see the Agate is good looking on the outside and is in banded layers of quartz. The geode is a dull ugly rock on the outside that has partialy filled in with quartz crystal. The pages given fill in the details well.

[TristanVT]

Originally Posted by Jinx

Anyone know the difference between these two rocks? I've never been able to discern a difference when (a) seeing pictures in rock books nor (b) seeing these in shops with other polished gems. To me, agate always comes as slices - resembling cross sections from geodes. Is this correct, or are they two distinctly different things?

Agate is quartz in a cryptocrystaline form. Geodes are primarily qaurtz in various forms, an outer layer of agate and crystaline quartz inside.