Our sudden interest in crystals turned out to be extremely timely, as last Saturday was the Friends of the Geology Museum's Winter Workshop. The topic was "Bubbles of gas in lava that solidified as they cooled and then are gradually filled by the crystallization of impurities in ground water seeping through." If that's too complicated for you, you can go with the museum's title: Geodes.
We learned how geodes form (see bubbles, lava, and impurities, above), saw pictures of geodes big enough to be a bathtub (but the sharp edges of the crystals would be ever so unpleasant on the backsides, so not recommended), learned that completely filled in geodes are agates, learned that beautiful purple geodes can be found in both South America and Africa from a place where they split apart from when they were part of the super-continent Pangaea, and were informed that when illustrating the part of of a talk about unearthing geodes in Chihuahua, Mexico, an Internet search for images almost uniformly yields small canines.
The highlight of the whole thing was cracking geodes:
And a bonus picture of Beeb rockin' the safety glasses (and badly needing a haircut).
Aren't they pretty?
The clear, sparkly stuff in the one on the right (belonging, appropriately princess-like Bean) is quartz. Four quartz make a gallon doncha know. The one on the left is Beeb's and has layers of chalcedony (the milky, bumpy stuff) over quartz. The one in the middle is mine and has a wonderful combination of chalcedony bumps and worms and sparkly quartz. Bug squirreled his away into his lair long before the photo shoot, so you'll have to take my word for it that it was equally cool.
Here's a close-up of mine:
The grand finally was getting to see these Trancas geodes under short-wave ultraviolet, which made them fluoresce green!