Iowa is a surprisingly diverse state when it comes to minerals and gems that can be pulled from the earth. There are a lot of interesting things hidden in the creeks and bedrock of the state, you just need to know what to look for and where to look.
That aside, let’s take a look at a list of rocks, minerals, and gemstones found in Iowa so that you can get a better idea of where to conduct your next hunt!
Minerals and Gemstones Found In Iowa
Calcite is a common find across the world, with a ton of regional variations. The most important one found in Iowa is dog tooth spar, a relatively rare form of calcite that forms jagged spikes across a surface. They make for interesting specimens, especially when they’re found integrated with other crystals.
Calcite is a soft mineral, vulnerable to even weak acids like vinegar. This vulnerability comes from its chemical makeup: calcium carbonate dissolves readily at a lowered pH in most solvents. The stone itself is easy to carve and work with if you’re a lapidary, but it’s not suitable for anything more dangerous than sitting on a shelf.
Iowa also produces another rare form of calcite, the so-called “Iceland Spar.” This is unusually transparent calcite, showcasing the unique optical effects of the mineral. It cleaves into pieces shaped as rhombuses easily. It’s thought it was the source of the “sunstone” in Norse myths.
If you’re looking to find calcite in Iowa, the following places are great:
- Southeast of Dubuque
- Near Cresco
- North of Stratford
All of these locations are known to host calcite, but there are far more places in the state where it may be lurking.
Selenite is a form of gypsum, and probably the favorite of most rockhounds. It appears as long, clear crystals in most cases. While soft, these interesting mineral specimens are surprisingly common and sold at most rock shops. Different varieties have their own local quirks of course.
The selenite from Iowa often has black inclusions forming intricate webs of dark moss in the crystal. While visually interesting… it’s just sand or dirt that got trapped in the gypsum as it crystallized instead of anything more exotic like tourmaline or rutile. I find that it makes it more appealing, but it’s not commonly seen in commercial sources of the mineral.
Where there is selenite, there is also gypsum. Iowa uses a lot of its gypsum to produce plasterboard/drywall. This consists of grinding the mineral into a powder and then putting it under pressure with additives before the paper is put down on each side. It’s the most common building material for indoor walls by far.
Selenite appears in the following counties, among others:
- Dallas County
- Plymouth County
- Polk County
Your best bet is to look for places that provide gypsum to the commercial market and then find a safe, legal place to dig nearby.
3. Iron Pyrite/Marcasite
Pyrite, or iron sulfide, is a brassy mineral that arranges itself into cubic crystals. It’s often called “Fool’s Gold” since the stone is closely associated with actual gold, making it easy for a new prospector to confuse the two. When this close proximity was studied it was found that iron pyrite can be a surprisingly rich gold ore, coming in at up to .25% of the stone by weight.
This discovery still doesn’t have people rushing to grind up and process pyrite. Instead, a lot of iron pyrite is found as a waste product in other mines or just ends up in the mineral trade. Most of us have at least one piece bouncing around our collection, its unique appearance makes it hard to resist.
Marcasite is almost chemically identical, simply having a different charge in its iron atoms. This mineral appears as a dark, iridescent crystal that is arranged into orthorhombic shapes. It often co-occurs with pyrite in the wild and can be found in many of the same locations.
In Iowa, the following are all good spots to look for pyrite:
- Black Hawk County
- Volga River
- Dubuque County
As the most common of the sulfide minerals, pyrite appears in more places than the above as well but those spots (particularly in Dubuque County) will serve you well as a starting point.
4. Petrified Wood
Petrified wood isn’t really a mineral of its own. Instead, it’s some form of silica that has replaced wood that fell in ancient mud or ash. As a general rule, it’s safe to assume that any petrified wood you find is some sort of chalcedony, but opalized pieces do appear at times. While there aren’t any petrified forests unearthed in Iowa, there is an abundance of small pieces found in creeks and streams.
Petrified wood is hugely variable in color, depending on the location. While much of it simply resembles wood there are also things like the rainbow conifers found in Arizona or the chromium-colored green petrified wood from the Pacific Northwest. Unfortunately, the wood here appears to be mostly brown and white, rather than bearing more exotic colors.
That’s not a bad thing, of course. While lapidaries love the more exotic woods, there’s something interesting about a fossil that’s maintained a color close to the original wood. These fossilized chunks can be found as limb casts or, more frequently, found along stream and river beds where they were deposited by ancient glaciers.
In Iowa, the following places are good to check:
- Jackson County
- Dubuque County
- Gravel Pits near Muscatine
In addition to the various waterways, the above places have more petrified wood than average for the area.
The various forms of cryptocrystalline silica show up… everywhere. If there is igneous rock nearby, ancient glacier movement, or just a waterway there’s usually some form of jasper, agate, or chalcedony. The location of the initial formation has a lot to do with how the stone looks, including the colors and patterns contained within.
Agates in Iowa tend to be banded, waterline, or dendritic without exotic coloration. However, in the Northeast of the state, you can find Lake Superior Agates. Jasper is found in red, often with striking bands of other colors that cut through it. Chalcedony also shows up on occasion, usually just as busted, single-color pieces of agate.
These stones are commonly hunted for in most areas, and often form the basis of a collection. The nice thing about hunting for agate and jasper is that it’s a rare trip where you won’t find something. I have yet to return from the field without at least one, its just a matter of learning what to look for.
For those hunting these stones in Iowa, the following locations are of interest:
- Quarries in Keokuk County
- Muscatine County
- Dubuque County
Just start looking in streams and you’ll stumble across something soon!
Glauconite is a fascinating mineral, and one that’s often kept in collections. The green crystals that make it up are very fragile, breaking into pieces with very little pressure. It’s most often found growing on sandstone and separation from the host rock is a delicate matter. If done properly, however, a glauconitic sandstone chunk can make quite a prize.
Glauconite has been used as a pigment (earth green) and is a primary component of greensand. The latter is an important source of potassium in fertilizers, making this mineral a bit more than simply a pretty but fragile crystal. It’s also found in geodes occasionally, often as growth on another mineral.
Glauconite most frequently appears interspersed with the host rock, giving it a greenish color. It is only found as a crystal rarely and I was unable to find any crystalline specimens coming out of Iowa at this time. The crystals are thin and needle-like, requiring even more care to handle than sandstone with a good growth of crystals.
If you’re interested in digging a bit of your own then you’ll want to check sandstone in the following places:
- Allamakee County
- Keokuk County
- Lee County
These areas are all host to glauconitic sandstone, but Keokuk offers the best bet for samples as long as you don’t mind them being in a geode.
Geodes are round-ish stones with hollow cavities in the center. This cavity is usually lined with crystals, most often quartz or calcite. Geodes are often among the first stones that get a rockhound interested, there’s just something magical about opening them up. In some locations, there is actually an abundance of different minerals found in the various geodes of the location.
Fortunately, Iowa is one of those locations. Iowa is host to numerous geodes from the area around Keokuk. In fact, Keokuk geodes are so famous and varied that they’re actually a subject of their own. Most finds will be simple calcite or quartz, but rarer minerals do show up at times.
Cracking a geode should be done carefully with a chisel in the field. At home, they’re usually cut with a rock saw or a wet tile saw, opening them up cleanly to reveal the interior. Some of these geodes are worth a surprising amount, Keokuk geodes are seriously collectible.
As you might have inferred, geodes in Iowa are best found in the area around the town of Keokuk. This region is host to an insane amount of geodes and it’s a bucket list spot for many rockhounds.
Galena is a fascinating ore and a primary source of lead for much of the world. Here the toxic chemical is locked into a chemical bond with sulfide, creating lead sulfide that crystallizes into black, cubic crystals as its most common form.
Lead gets a bit of a bad reputation for the havoc it plays on our nervous system. While you should certainly take care when handling lead (or associated ores like galena), it’s an important part of many industries. Iowa produces quite a bit of galena, although not as much as some of the other states in the same region.
The galena found in Iowa is often high-quality, but not silver-bearing. Argentiferous galena is actually a big source of silver, but not all galena has the white metal locked into its matrix. In Iowa you’d mainly be looking for high-quality specimens, there isn’t an appreciable amount of silver in the ore here.
For those interested in hunting for their own samples, you may want to see what you can do about finding mine tailings in the following counties:
- Clayton County
- Jackson County
- Dubuque County
Be safe, but the easiest way to find galena in Iowa is to find mine tailings in areas where commercially viable amounts of galena are found.
Feldspar is one of the most common minerals on the planet, making up a large portion of the dirt and stones that we see. In particular, feldspar is often found in igneous stones like granite which make up one of the colored spots that the material is known for. In Iowa, the vast majority of feldspar found is locked up in granite as tiny pink crystals.
On occasion, you’ll be able to find larger crystals in Iowa, primarily in limestone deposits. The areas where granite and limestone meet are the best spot to take a look. The feldspar in this state is primarily composed of potassium feldspar. The feldspar you’ll find is usually light pink or off-white, with some more included brown specimens also appearing.
Feldspar seems to be mainly found by hunters while they’re looking for other things. Thus you might just want to consider the possibility you’ll find some and take a look at anything with tabular crystals a bit more closely. While rare, you can find some interesting specimens on occasion.
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