MIDWEST USA SEDIMENTARY TYPE GEODES

Bob,
Would you consider uploading your geode images to our general gallery? When they are left as attachments, they are hard to locate after a while and get buried in the mass of old messages. If you would like detailed instructions on how to do this see [www.mindat.org]

Rock Currier
Crystals not pistols.

This geode is from Harrodsburg, Monroe County Indiana, but is from the RT37 cut about a half mile north of town. 6x5.5x6.5 cm. Circa 1964.



Bright quartz with spheres of calcite of max 0.5 cm size.

Cheers!

Steve



Edited 1 time(s). Last edit at 03/20/2012 02:58AM by Stephen Rose.

WOW i have never seen spheres of Calcite in an Indiana geode, very very cool.

A little removal of shadows in Photoshop make you image look like this.



Rock Currier
Crystals not pistols.

Great and interesting pix Stephen! So, continuing on this theme of hemispheric carbonates in Indiana geodes, these pix show additional examples. The first and second pixs are of both crystalline (dissolution) calcites and numerous hemispheric calcites to 0.6 cm in an 18 cm geode. There is also some minor barite. Found 2006 from Monroe county. The third picture is 2 examples of hemispheric aragonites in 2 different 8 cm geodes from Monroe county, found in 2004 and 2005.

Rock, it's magic!

Byron, Bob has shown some great examples of the calcite "spheres." I recall that there were good examples at the R37N (aragonite) location in Monroe County that were not very uncommon. Snow white perched on dark ankerite in some cases.

Cheers!

Steve

Hi Guys,
So the white ball shaped crystals from the aragonite road cut are aragonite or calcite? Seems we found three like that, very neat pieces. The structure reminds me of prenhite!!


thanks
E

Yes Dorothy, there are copper minerals in Indiana geodes!! Here are 3 examples of MALACHITE in Indiana geodes. The first is a hemispheric malachite microcrystal (?) to about 3 mm with nearby hemispheric calcites to 7 mm in size. Monroe county 2004. The second pix is of malachite on a grouping of hemispheric aragonites (yes aragonite!!). The whole grouping is about 1 cm, from Monroe county 2005. The last pix is of a 3mm malachite crystal with nearby aragonite coating quartz. Also, Monroe county, 2005. The question of aragonite vs calcite hemispheres has intrigued me over the years as I have many examples of both. Showing some of "each type" to several identification experts seems to confirm that in aragonite locales, the hemispheres are different and probably truly aragonite while other locales seem to have true calcite hemispheres. Incidentally, I also have chalcopyrite microcrystals and some are altering to malachite in several Indiana geodes. All these examples are from one aragonite locale in Monroe county. Go figure........, but enjoy! BOB

Everett,

Good question. I don't think that we ever tested these specifically but assumed calcite. To me they seem like they could be a form of the worm-like aggregates of calcite that are composed of very thin rhombs stacked on the C axis. These are late in the paragenesis and post-date or overlap aragonite as I recall.

Cheers!

Steve

Colorful and very collectible CELESTINE crystals are found in geodes in Lawrence and Washington county quarries in Indiana. All 3 pix show 8 cm x 4 cm geodes containing 2.5 - 3.0 cm blocky celestine crystals with some minor calcites. The first pix is from the old, now flooded and extinct Mitchell quarry in Lawrence County. The 2nd and 3rd pix are from still active Salem quarry in Washington county. Many floater crystals of celestine from this quarry grace collections and museums around the world. Mineralogical Record had an article on the minerals of this quarry about 1983. Several local clubs still are lucky enough to gain yearly entrance to this quarry, but very hi quality finds are now few and far between.

Bob,

The geodes showing malachite are really interesting. I have only one Indiana geode showing chalcopyrite with malachite alteration associated and it is from the aragonite location on SR37, 5.25 miles north of Bloomington in Monroe County. What is more interesting, I didn't know about the chalcopyrite until the day before you posted your malachite pictures! It only took 48 years. I was looking for a new geode to photograph and found it in a box of inexpensive mixed things that I have been selling to kids over the years. I suppose that I had kept it for the ankerite and calcite but never took a close look at it. It is vintage 1964 and should have been noted in the 1966-1967 Rocks and Minerals article but was not.



Chalcopyrite, malachite (left center on quartz), ankerite, calcite and quartz geode. 4.5x4 cm. Chalcopyrite crystal approximately 1.0 mm. Circa 1964.



Here is the best I can do with my camera through a 10X lens for the little chalcopyrite with malachite.

Cheers!

Steve



Edited 2 time(s). Last edit at 03/24/2012 05:10PM by Stephen Rose.

No discussion of Midwest geodes would be complete without talking about very large "field and stream" geodes. So, I went back and reviewed mindat's archive pages from the last several years and indeed there have been several posts, during that time, regarding these large geodes, usually involving their collector value or some such similar question. Here is my take and summary on the subject. These geodes are found in fields and stream beds. They can weigh from about 40 lbs to 350 lbs here in Indiana. They usually are collected and displayed UNOPENED and, when opened, are solid or have a relatively small cavity with dingy rusty/muddy appearance. They, only very very rarely, are nice and fresh inside. As such they have little collector value, being sold unopened (at lawn and garden shops) by the pound rather than by their inside appearance. Their uses therefore, include display, unopened, in rock gardens or around a home porch, as pictured here. Also, they are displayed, unopened, in museum hallways and entrances to geology exhibits in university geology buildings. These examples are usually donated to the museums or universities and never bought by the university or museum. So, as mentioned, they have little to no mineral or geode collector value as they are too bulky and heavy and ugly to display in a private collection or cart around to mineral shows etc. As such, for example, a 100 lb geode would only have a per pound weight value of about $50 - $100. I hope this summary answers some questions out there. BOB

STEPHEN That is about what my chalcopyrites altering to malachite look like; they are hard to photograph and not very displayable. Also interesting that they all come from aragonite locales. Yours was along Indiana route 37 in Northern Monroe county and mine in Southern Monroe county. I think these are all in the Ramp Creek formation of limestone; if so, there is a small bit of copper in it...... Cheers BOB

Bob,

I had to look it up....nomenclature changes in the rocks. Ramp Creek fm is now what was the Lower Harrodsburg fm. Maybe a good exploration tool for you geode hunters?

Cheers!

Steve

I'll post one more, a bit smaller than those in Bob's last posting!



Baryte, SR37 about .75 miles north of Harrodsburg, Monroe County, Inidana.

Pale, grey-blue bladed crystals in a small quartz geode. The possibility that this is celestite was considered as strontionite is reported from this location. However, it does not seem likely as celestite is not reported as a geode mineral from this or any of the numerous locations around Harrodsburg. Overall size:4.5x6x4 cm. Baryte cluster is 0.8 cm tall. Circa:1965.

Cheers!

Steve

Great stuff guys! Enjoying this thread. Who doesn't like geodes? Those malachites are way cool and those blocky celestines... they are celestial!

regards,
stephanie

Indiana geodes host a number of secondary minerals that are not commonly found. In addition to my previously pictured malachites and the chalcopyrite that I alluded to (and Stephen Rose pictured), here are several other rarely found minerals in Indiana geodes. The first pix is of SELENITE variety of GYPSUM. The needles are on quartz and adjacent to a calcite and barite. This geode is about 12 cm, from Monroe county, 2008. The second pix is of a small purple FLUORITE in a small 1.5 cm geode. I only have this one example and have never seen another, altho "it is reported to occur". From Harrison county, 2000. The third pix is of STRONTIANITE on quartz with adjacent barite. There are multiple white "puff balls" of strontianite; this one is also from Monroe county 1980s and again is the only one I have, but "reported to occur". Enjoy.......... BOB

Another small specimen from the SR37N (aragonite) roadcut 5.25 miles north of Bloomington in Monroe County. Collected in 1964/65.


Smythite/pyrrhotite inclusions in pale yellow baryte with dolomite and quartz. Geode opening 3x3 cm.


As above, magnified. Baryte crystal is 1.0 cm. long.

Smythite is quite common at this location and is almost always associated with pyrrhotite with one or the other being predominant in a given specimen. It is usually found as inclusions in calcite, rarely in baryte. One specimen of free-growing smythite was found during this period and xrd identified.*

Cheers!

Steve

*Bob, this one went to the Harry Sering geode collection as well.

STEPHEN Smythite was first identified in Indiana geodes; I believe it is the only mineral first identified in Indiana. As you alluded to it is quite common, especially as 1mm six sided plates within barite crystals and occasionally in calcites as well. It was previously thought to be marcasite crystals. About 3 years ago, John Rakovan a geology professor from the University of Miami, Ohio requested some smythite from me as his students were working on a paper about it. I provided him enough for his research and, I believe, the paper was presented at the Rochester, NY symposium. In an upcoming post, I will show some pix of barite with smythite. CHEERS............BOB

I enjoyed the smythite discussion. I know goethite can be found in both Keokuk and Indiana geodes.
This photo is a geode from Clark County, Missouri - having the longest goethite needles I've ever found - the longest is 1/2".


This photo shows black goethite needles in a 3-1/2" diameter geode from Hancock County, Illinois.



And this is a photo taken through a microscope of a double terminated goethite crystal in the above geode. The dots appear to be micro rosettes of red hematite crystals. I can't recall the magnification used.

The black goethite crystals I have found in Indiana might be pseudomorphs after capillary marcasite because they have the sword blade shape instead of the pencil point shape like those above.