There are several types, strange formations, and nicknames for the Keokuk geodes. I will try to describe these with the help from my wife the photographer. If you know of any more I haven't mentioned, by all means, send an email. The first two types are my favorites, so I paid a lot more attention to them, sorry.
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Snowball - Gorgeous citrine snowball: Snowballs are chalcedony globes formed inside the geode cavity and may be covered in quartz crystals or calcite crystals, or chalcedony.
Snowball - Large gray chalcedony snowball: The damage to the top of this snowball is very common. The 'lid' is often times attached to the snowball and damages the 'ball' when cracked.
Snowball - Perfect snowball with calcite: The shell disintegrated and left a perfect ball with only a small attachment to the shell.
Snowball - Quartz with dolomite: This is a snowball's insides. This ball was broken by nature sometime in its early life, and resealed back together with pretty quartz crystals. The insides of a snowball are usually solid. If it has a cavity, the crystals inside are sweet. I saw a geode of this type with light amethyst crystals.
Snowball: Brown calcite coating a snowball on quartz.
Snowball - Quartz snowball with calcite: Not all snowballs are round. This one captured the moon and made it sparkle.
Dewdrop diamond - Dewdrop diamond with clear 'diamonds' and calcite: The dewdrop diamond is white chalcedony sprinkled with small hexagonal dipyramid crystals of quartz similar to the Herkimer diamonds from New York state. A few blue chalcedony dewdrops came out of one, now permanently closed, location in Clark Co. Mo.
Dewdrop diamond - Blue chalcedony dewdrop with calcite: The shell on these geodes is very hard and the calcites in them are often fractured when cracked.
Dewdrop diamond - Deep smoky dewdrop diamond: These geodes sparkle brilliantly in the sun and pictures do not do them justice.
Dewdrop diamond - Smoky dewdrop diamond: Have you heard these geodes are one in ten thousand? It depends on where you look. I have found 19 dewdrops and that means I have cracked two hundred thousand geodes... That's not right.
Herkimer Diamond - Herkimer diamonds with calcite: I had the privilege to bust rock near Erie New York. This is the best specimen from that trip. I hope you know these are not REAL diamonds. Yes... I know this is a vug and this page is about geodes... chill.
Floater - A floater next to a fossil geode: These geodes are so light that they can 'float'. I have seen a geode bobbing and sinking in a rain swollen creek before, but no geode can float. These geodes are better left whole so folks can 'feel' the experience. The crystals are usually compromised by dirt getting through cracks in the super thin shell. The lophophyllidium proliferum (horn coral) fossil plainly exposed on the geode to the left of the 'floater', verifies the sea shell origin of the Keokuks.
Blue Navoo: Snowball I dubbed the 'blue tornado'. These geodes got their name from the blue shell that would translate into the geode cavity. Found abundantly in only two spots (that I know of) Highway 61 near La Grange Mo. and the Sheridan creek area on the south edge of Navoo. Both of these areas are No Trespassing.
Blue Navoo: Dolomite on quartz. The gemmyness (not a real word) or sparkle of the blue Navoo's is marvelous. Literally. It just leaps out at you. The blue color fades to gray/blue shortly after cracked; probably from drying out. When soaked in CLEAN water, the blue color returns for a few weeks. The blue Navoo's pictured on this website were not soaked in water, so... gray/blue Navoo?
Kahoka black - Black calcite on quartz: This is not a good specimen... being without a few big iridescent brown calcite cubes. These are impossible to find and very expensive. Ill probably never own a good one. Heralded as the top geode to have in your collection.
Aqua geode - Good candidates: The water in a geode can be very good... or very bad. If it is 'old' water the gemmyness (not a word) is a wonder to behold. If it is 'new' water that has made it in through the cracks of the shell, it is bad indeed. Compromised is the word I use.
White/red rind geode - Calcite on quartz in a red rind geode: During a period of silica saturation, a layer of white/red chalcedony was laid down on the interior of the shell. Different colored crystal layers followed and a very distinct white/red ring is displayed when this type of geode is cracked. The best of this type, in my opinion, is when the white/red layer lays just below the quartz crystals letting the color bleed through; similar to a dewdrop diamond.
Smoky geode: Smoky quartz geode. Smoky's are common in the Keokuk geodes and a good geode like this is easy to come by.
Brown Calcite geode: Brown calcite with secondary clear calcite. Many of these beauties were found by Geode Man and are displayed on his wife's web site (Theresa rocks). This man was the first on the web with the Keokuks, and in my opinion, his revitalization of the interest in the Keokuks, was/is invaluable.
Dogtooth Calcite geode: Pink/white scalenohedral calcite with a spot of black crystals. The color change in this type of geode is strange indeed. Many theories exist. Most likely it is caused by kaolinite absorption. This geode is common where brown calcites are found. Finding one with the color change is not so common.
Chalcedony geode: Blue chalcedony lightly coating quartz crystals. Chalcedony is quartz crystals so small they can't be seen. Sometimes this coating of micro quartz isn't so nice. The chalcedony crystals pick up other minerals in their structure, and can be any color. If it is an ugly color, and it coats large sparkly crystals, it is called leaverite.
Chalcedony geode: Blue Botryoidal chalcedony with aragonite crust. This is the stuff that forms the "ball" in the snowball geodes.
Citrine quartz geode - Orange/yellow quartz: Very common color for the Keokuks. This is not an iron coating that can be cleaned by muratic acid.. This is the iron mineral goethite underneath, and sometimes included in, clear quartz crystals.
Red quartz geode - Rose and citrine quartz: The colors come from the iron minerals hemitite and goethite, The reds are the second most sought after Keokuk geode. I don't hunt for them specifically, but I sure am happy when one shows up.
"Leaf" formation - Clear and yellow quartz: This basketball sized specimen has the perfect "leaf" dominating the cavity. Found during a Geode Festival 2009 hunt on the Fox river.
"Leaf" formation - Micro pyrite on quartz: The "leaf" was created when two connected calcite nodules (future geodes) shared wall was poorly formed. The two nodules, having a shared side, fused together into one geode. The poorly formed wall that the two original nodules shared, is now a "leaf". If the wall the two nodules shared, kept its structure (during the acid 'melt') and stretched across both insides of the geode, it is called a 'bridge'.
"Bridge" formation - Three quartz bridges: Four calcite nodules, with quartz saturated shells, were fused together and formed one nodule. When the nodule was exposed to the near-surface, acid rain melted the calcite leaving these three "walls" to be coated in crystals in a later deep-burying cycle. There is a geode owned by Jim Sheffler that has an entire geode, shell and all, within another. Check out this critter when you go there to dig. The Geode Kid has several thundereggs showing the same abnormality. By all means, visit his site and check out the polished eggs from his Baker Ranch claim in New Mexico. Mercy day!
"Bridge" formation: Clear and yellow quartz.
Aragonite geode - Aragonite on dolomite with calcite on quartz: Crystallized aragonite is not common in the keokuk geodes. It is more common as crusts or smooth balls. When a specimen is found with visible crystals, it is highly prized. In this type of geode however, crystallized aragonite rules. This type is found in isolated pockets at several geode locations in Hancock county Ill.
Aragonite geode - Aragonite on dolomite with calcite on quartz: The same geode showing the aragonite crystals. The geodes containing the aragonite have an area of the shell that is very thin. While this allowed the hot liquids containing minerals to flow more freely when it was deep-buried, it also allowed the geode to be compromised by near-surface dirty water, later in its life. I have yet to find a clean (gemmy) geode of this type. The geodes of this type that have thick shells have only quartz crystals and no secondaries.
Pandora's box geode: Blue barite 'flower' with dolomite, calcite and kaolinite on quartz. Notice the 'healed' shell at the top and bottom of this geode. This type of geode has been crushed or flattened by the weight of the ground during a deep-burying cycle. Sometimes the crushed geode is 'healed' by hot mineralized fluids, but the cavity is downsized and in most cases the geode is rendered solid. When a cavity remains, the secondaries are numerous and uncommonly large. I never toss this type of geode, even though it may seem solid, without giving it a little tap with a hammer to check for a hollow spot. Hint... This type, having a poor outside appearance when whole, has some of the finest secondaries ever found.