Rocks from the final frontier

Written by Peggy Fisherkeller, curator of geology at the Indiana State Museum

One of the best parts of my job is meeting people who take their hobbies to the extreme. I might like to look at antique dresses in a book or in a museum, but probably wouldn’t go beyond that. However, there are those special people: collectors of information and objects that are always gathering more in an effort to quench their addiction.

A grouping of Sikhote-Alin meteorites. Photo courtesy of the Indiana Geological Survey.

Meteorites inspire that kind of collecting. Most meteorites are not particularly attractive — at first. They usually come in varying shades of brown. ‘Lumpy’ would be one way of describing a typically-shaped meteorite.

But then you start to think about it more. That hunk of metal didn’t come from the railroad yard — it came from outer space. It could very likely have come from the core of a long-gone planet, the bits of which have been floating around the void for millennia. Probably only recently did it intersect Earth’s orbit closely enough to be pulled in by gravity. And now there it sits.

We’ve got some sitting here on the first floor outside the R.B. Annis Naturalist’s Lab now through the end of July. The meteorites were selected from two local collections to show a range of types. Personally, it was a pleasure putting it together. I really didn’t know very much beyond the meteorite basics when I first came to work here, but the opportunity to talk with enthusiasts has given me a lot more to think about. Enjoy!

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The secret of geodes

geode011As a person who holds a bit more knowledge on certain obscure topics than the general population, I’m sometimes considered a specialist, at least in regard to rocks and fossils from Indiana. That being the case, I often entertain visitors who bring in bizarre objects for identification. Among the most common objects to come through the door are geodes. A fashionable Indiana rock, geodes are mostly found in Morgan, Monroe, Brown, Lawrence and Washington Counties. Most natives of those counties could tell a geode from an ordinary rock, but those of us not born and raised in south-central Indiana often don’t know the identity of these unique natural objects. Geodes are often suspected to be a number of things, including petrified human heads and dinosaur eggs. Unfortunately, neither of these is true. However, they are a minor mystery to geologists.

geode02Indiana geodes originated about 350 million years ago, along with rocks that were deposited while Indiana was underwater (think of a briny middle-eastern tidal flat – very salty and very shallow). The prevailing theory is that geodes originated as an under-sea-floor nodule of the mineral anhydrite. Conditions changed and the anhydrite was replaced, through groundwater flow, by other minerals, resulting in the vast quantity of geodes that we see in only certain rock layers today. By definition, geodes have a hard chalcedony rind, and can either be hollow, with their walls lined by various crystals, or solid.

Many people collect geodes. In southern Indiana, many a fence row is made up of these hard lumpy spheres. They do have another aesthetic value, though. Crack a geode open and you might just find some spectacular crystals, presented nicely in a bowl.

The museum has a collection on display, but through May, a local geode collector, Bob Harman, has been kind enough to loan us some of his best specimens. These are on display in our first floor natural history gallery.

Peggy Fisherkeller is the curator of geology at the Indiana State Museum.