About Keokuk Geodes

What is a Keokuk geode?

     A geode is a spherical shaped rock with a crystalline interior.  There are two main characteristics that makes a geode different from any other rock.  First, is that all geodes have a bumpy exterior that resembles cauliflower.  Secondly, most geodes have hollow interiors with crystal formations growing inward towards the center of the void.  The more hollow the geode is the more valuable it is to scientists and collectors.


How are geodes formed?

     There are many theories out there to choose from,  but the most agreed upon by geologists is that, originally the geodes were nodules with crystal growth around a nucleus or core, and the solid concretions some how got desolved leaving a hollow void. The minerals we find inside were transported by groundwater solutions and left behind as replacements of the geode walls or as crystalline growths within there interior cavities. (Geode brochure, Iowa DNR, 1995) 

     This is good, but I believe geodes are formed when a void caused by decaying organic material is filled with mineral rich groundwater fluids deep on the ocean floor.  The fluids get trapped in the void when the elements in the geodes form minerals, most commonly quartz - Si02.  These minerals are forced to the interior walls of the void due to the extreme pressures caused by the weight of the ocean water.  Once the minerals settle, the microcrystalline quartz crystals form layers trapping the larger elements inside, thus starting the formation of the geode.  The quartz crystals grow from the outside in, and are not dissolved away.  I've seen no physical or chemical evidence to support the minerals being dissolved.  The different minerals that form in Keokuk geodes are dependant on what elements were left in the fluids that remained inside and available during formation. 

Where can I find Keokuk geodes?

     Keokuk geodes are found in the Warsaw formation.  This formation is exposed in approximately a 50 mile radius around Keokuk, Iowa.  This layer also extends into Illinois and Missouri. Although, geodes in this layer are found in 3 states, they are still referred to as "Keokuk geodes".  This formation is characterized by two distinct geode bearing layers a gray shale layer and a brown carbonate rich clay layer.

     The lower level is made of a gray shale.  The shale is very hard and the geodes do not come out easily.  These geodes are very clean on the inside and don't require much cleaning once opened.  The geodes can be dug out of the gray shale using rock hammers, chisels, pry bars, sledge hammers, and paleopicks.

     The second layer is a brown carbonate rich clay.  This layer is much softer than the gray shale and I've found that it produces many more hollow geodes.  Geodes can be extracted from the brown clay by using a paleopick, rock hammer, or even a small shovel (spade).  The geodes in this layer require some cleaning once opened due to some iron and calcium deposits that have coated the quartz crystals during formation.  The best time to dig in this layer is after the winter thaw and following heavy rains.  The thawing ice and flowing water loosen up the clay for easy geode digging.  If you're not one to dig, many rivers and creeks in the Keokuk area have cut though these two layers and weathered out the geodes for us.  Geodes along these streams and rivers can be easily picked up along the bottom of the water way or on rockbars and sandbars.


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What minerals can I expect to find in a Keokuk geode?

     There have been 17 different minerals identified in Keokuk geodes.  The most common minerals are: Quartz, Chalcedony (microcrystalline quartz), Calcite, and Pyrite.  You may occasionally find: Sphalerite, Aragonite, Hematite, Kaolinite, Dolomite, Ankerite, or Limonite (iron staining).  You could find: Barite, Millerite, Malachite, or Selenite. And if you're lucky, you may find one of these two: bipyramidal quartz or Stilpnosiderite. Bipyramidal quartz is what is found in the rare diamond dewdrop geodes and stilpnosiderite is the mineral responsible for the formation of the highly prized, iridescent brown calcite geodes.

How do I open a geode?

     There are 3 commonly used ways to open a geode: using a hammer and a chisel, cracking them with a pipe cutter, and cutting them with a lapidary saw.  The first way is the most common, the hammer and chisel method. 

     First, you want to find the center of the geode.  Once you've decided where the center is, grab a hammer, a chisel, and a pair of safety glasses and start tapping a line completely around the geode.  We will call this the center line.  The size of the tools you use will depend on the size of the geode.  The larger the geode, the bigger the hammer and chisel you'll need, and how hard you hit each strike.  You will continue to chisel on this center line until a crack is formed. If you did this correctly the crack you make should follow your center line.  Continue to chisel, slightly decreasing the strength of your strikes and follow the crack until it gets larger and breaks into two halves.  Don't get frustrated if this doesn't work perfectly the first time you try it.  This method takes a lot of practice. Give yourself plenty of time and don't rush it.  If you do, you won't get two equal halves, but a pile of sparkly crystals that used to be a geode.  Trust me, I've done it.   This is the method I used to use to crack open all my geodes until I bought a pipe cutter.  I still use this method to crack open the larger geodes, any geode over 11 inches in diameter. click there --> Printable instructions


     Secondly, is the pipe cutter, or geode cracker method.  This is how I break open all of my geodes under 8 inches in diameter, and when I go to shows.  Using this method gives you the best chance of an even break.  Just like the hammer and chisel method, you'll want to find the center.  Once you've found the center line, you wrap the attached chain around the geode, tighten the set dial, and sqeeze the two bars together, and POP the geode opens right where you want it.  It's just like cracking a walnut with a nut cracker, without the chain.  The chain directs the pressure along the center line for an exact break. This is how I crack the "open your own geodes" at shows. It gives the buyer the joy of opening the geode themselves and allowing them to be the first to see inside.  The kids and their parents really enjoy the hands-on participation they get in this activity.  It also makes any onlookers curious enough to come over and join in the fun.


     Lastly, is  using a lapidary saw.  I don't recommend using this method unless you plan on polishing the geode halves.  The saw leaves circular markings as it cuts through the quartz, and it's not an attractive show piece.  This is by far the most expensive way to open a geode, prices range from $1.00 - $2.00 per inch to cut the geode in half,  and $4.00 - $6.00 per inch to polish each half.  Unless you know someone to do this for you, the flat vibrating laps cost $1,000.00, and the saws cost about $3,000.


How do I clean geodes?

     The best way I have found to clean a geode is by using Super Iron-Out to get rid of the iron staining and Muriatic Acid to dissolve away any unwanted calcium deposits (see note below).  It's important to follow the directions on the labels of the two products for safe use and proper water mixtures. Once mixed with water, I soak the iron stained geodes in the iron out mixture overnight, the calcified geodes in the muriatic acid mixture for 4-5 hours, and then rinse using the "jet" setting on a garden hose nozel.  I keep the iron out mixture and the muriatic acid mixture in seperate 30 gallon plastic garbage container with a lid.  This keeps the chemicals out of reach and safely covered to contain any fumes. Always store and use the chemicals outside or in a ventilated area. Always wear rubber gloves suitable for each chemical when removing the geodes to be rinsed. Both the Super Iron-Out and the Muriatic acid can be purchased from most hardware and home improvement stores.