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Unusual Metallic Rock, Identification Input Would Be Great


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3 hours ago, uknowhooiyam said:

if i want to know just what its content, i suppose a mass  spectrometer test would do that.

X-ray fluorescence (XRF) spectroscopy/analysis is likely less expensive, assuming you don't have inroads with a university.  Some coin shops and pawn shops have the device to perform that.  They may charge a fee or do it for free.  You could call around and ask.

 

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9 hours ago, uknowhooiyam said:

Im not too far from Davenport, the only thing about Centennial that rings a bell is the park.

It is also a cement quarry on the Mississippi and that is where they had found fossils and some gold nuggets. I didn't know if that was the location you were referring to or not. There are several creeks and rivers that do have gold and silver in them where you are at.

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  • 7 months later...

Thought that I would take a stab at this.

From the information supplied by the original poster, uknowhooiyam, my guess is this a bit of gash vein. Gash veins are common in massive limestone/dolostone where fluids migrate down (typically calcite veins) or up (basinal brines or other fluids trapped beneath) when fractures form.

Northeastern Iowa is on the western margin of the “Upper Mississippi” MVT district and has a history of  Lead/Zinc mining and considerable production. Mineralized gash veins are common in the district but are generally small and not of economic interest.

Looking at the first two pictures, the rock appears to have two well developed surfaces which I think are the sides of the vein. In the first picture, on the lower left and to a small degree in the upper right, there is a light yellow/brown material that has what looks to me like slickenside texture which would suggest that there was some movement between the vein and host rock post formation (what appears to be stepping or chevron texture). In the second picture you see some evidence of this, and there are scratches that suggest that the vein gangue is fairly soft.

In the third picture, what would be a cross-section of the vein, there appear to be well rounded pebbles, course/angular fragments of a gray/metallic material, in a granular matrix. The gray/metallic material also appears to form a more competent lower edge to the vein. The rounded pebbles (some look like chert or possible quartzite) and the angular fragments suggest that this was a dynamic system with either fluid flow or fault movement.

The original poster mentioned that in places the rock appears to have a “molten” appearance and I assume that he is referring to be the wavy appearance of the gray material on the right side of picture 1, and the rounded blebs of the gray material in picture 2. He also mentioned magnetic and “paramagnetic” “qualities”. I am assuming that what he meant was that a magnet was attracted to the rock, and that once the magnet was removed the rock itself became slightly or briefly magnetic (Hysteresis?).

OK, sort of a long explanation to back my guess. I think that this is a small gash veinlet from limestone/dolostone that was mined in upper east Iowa where MVT massive lead-zinc deposits occur. Botryoidal or coliform textures (the “molten” appearance) are common for the microcrystalline sphalerite/galena and possibly hematite. I’m guessing that the gray/metallic material is a mixture of those minerals and probably has a fairly high iron content (primarily hematite?) which would explain the magnetic properties. In several places on picture 3 the broken surfaces of the gray material also has a reddish/purple tinge which could support this. The blue/green material in pictures 1 and 2 doesn’t really look like copper staining to me, more like a green clay or glauconite (MVT’s are also generally copper poor). The other somewhat dark lime green that coats the fracture looks to me to be organic.

There is a good chance that all I have written here is BS, that can be the nature of geology (probably why I was fairly good at it), but hey, it’s been fun thinking about it.

Cheers

Bill

 

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On 3/15/2020 at 5:32 PM, GB_Amateur said:

X-ray fluorescence (XRF) spectroscopy/analysis is likely less expensive, assuming you don't have inroads with a university.  Some coin shops and pawn shops have the device to perform that.  They may charge a fee or do it for free.  You could call around and ask.

 

I have taken a few little pieces to have XRF tested as you suggest to a local pawn shop, the most they charged me was $10 and one time no charge at all.

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