Let's go geode-caching! Err... geocaching... Either way, this legendary geode shop here in Knott's Berry Farm Ghost Town is dishing out pieces of geologic importance every day. Let's take a look at what a geode really is.
Geodes always form in cavities, mostly rounded spaces in igneous and sedimentary rock. In igneous rock, cavities are usually caused by gas bubbles under the surface. The geodes themselves are made up of these cavities (with the outer shell of them hardened) filled with silicates and/or carbonates, minerals that were deposited inside. These depositions can come from groundwater or hydrothermal solutions. Hydrothermal means heated water from the earth's crust. These solutions can permeate into the cavity, leaving behind minerals that are allowed to crystallize inside. These crystals in the hollow chamber are the spectacular sight we see when a geode is sliced open (like here at the shop!).
How are geodes cut?
There are many ways to access the inner beauty of a geode. One, and what seems to be the most common way, is the hammer/chisel method:
Adapted from GeodeGallery.com:
HAMMER/CHISEL METHOD: This is the most popular way to open a geode since most people have a hammer and chisel available around the house or in a toolbox versus some of the more specialized methods that mainly rock collectors have that are listed below. To open a geode with a hammer and chisel, score the geode all the way around the circumference of the geode with the chisel. We suggest using a flat-faced (regular) chisel end versus the pointed type, since the force from a pointed chisel will be directed over one spot versus over a larger area with the flat-faced chisel (better chances of opening along the line you want it to open on!). Continue this process until you see a crack develop in the geode, and then follow the crack around the geode until it opens. If the geode is hollow, and you know it is hollow, you must be very careful to not strike the chisel too hard with the hammer. Start lightly at first and then strike harder (but not too hard) if a crack is not developing.
Next is the pipe cutter method:
PIPE CUTTER METHOD: Opening geodes with a soil pipe cutter is a more specialized method, and these tools are usually only found among the more advanced or serious collectors who have a large quantity of geodes to open. Pipe cutters have a chain that contains sharpened carbide-tipped roller blades that is wrapped around the geode and tightened. Unless the geode already has a crack in it (visible or not), the success rate for opening a geode into two nearly equal halves is very high with a pipe cutter and the process is very quick. Pipe cutters, however, are not usually cheap, and that is why they aren't used or available on a widespread basis. The sizes vary, but the most popular type is the soil pipe cutter that contains two arms with equal lengths and a "jaw" with the chain attached. Popular manufacturers are Ridgid, Reed, and Wheeler/Rex, and they can be purchased through most plumbing suppliers (these companies do not necessarily sell direct, you have to go through a distributor). The average price for a new pipe cutter of this variety is anywhere from $300-$600 depending on how long of a chain you want (the longer the chain the more expensive as most of the cost of the pipe cutter is actually in the chain). Some tool rental places also have these available for rent, contact rental businesses in your area for availability if you are opening a large quantity of geodes to justify the cost.
There you have it!
Logging this earthcache as found:
1) Send an email with the name of this geode-cache at the top
2) Take a moment to look at/in the shop. Describe how you think they cut the geodes (even if they are not actively cutting them, you should be able to still get some ideas).
Optional 3) Post pictures!
Sources:
http://en.m.wikipedia.org/wiki/Geode
http://dictionary.reference.com/browse/hydrothermal
http://www.geodegallery.com/breakinggeodes.html