Appreciate you accepting this as the answer, laundrygal-ga,
Here are several references which have several methods, ranging from using
a hammer and a sock, all the way to using a diamond saw, in order to open
up those unopened geodes you bouaght for your father.
By the way, great gift to buy for him! Until he opens them, he will have
no idea of what is inside, which can provide a wide range of results.
"How To Break Open A Geode!" from the Geode Gallery website.
"Place the geode in a sock and hit very lightly with a hammer."
"Opening Geodes" on the AlicatsRocks website.
"Check your geode for any hairline cracks. If you find one, take a flat
tipped screwdriver or a small chisel (depending on the size of the geode)
and carefully insert it into the crack."
"CRACKING GEODES OPEN (Without destroying them!)" from the Great South Gems
and Minerals, Inc. website.
"Another method of opening geodes that works well, (The method I use most
often.) is to crack the geode open with an old fashioned cast iron plumbing
"Opening and cleaning geodes" from within the KMF Rocks Newsletter.
"The third and most used method is to lay the geode in a soft (earth)
depression. Look the geode over for any cracks or weak spots. These should be
found and force applied there. When you have decided where you will apply
pressure, use a medium weight hammer and center punch. (Never use steel
chisel). Put the punch in a spot most likely to keep if from sliding off, and
hit it several times; easy at first, then harder. If three or four blows do
not open the geode, repeat in other spots until a crack does appear. Then use
a screwdriver to pry apart."
If you need any clarification, please feel free to ask.
Google search on: opening geodes
Also, I have had some experience with opening geodes.
Looking Forward, denco-ga - Google Answers Researcher