Interesting little rock

[Dougie Webb]

My wife and I have a habit of collecting rocks whenever we go somewhere new, and I think this was from our travels, so unfortunately cannot confirm where it's from.

The reason it's a bit odd to me, and why I'm here, is that it's both very light for its size and also magnetic. I discovered it was magnetic quite by accident when I happened to put a piece of magnetitie in a bowl with it.

So I said "hmmm.... magnetic and light? wonder what it's made of?" To my surprise, no matter how hard I tried, I could not get it to set off either of my metal detectors, full sensitivity, zero discrimination." I thought "well apparently I have something here that's broken the laws of physics as we know them - a non-metallic magnet." Alas, not so. I was *finally* able to get my pinpointer to sound off after rubbing the rock directly on it in all directions - and it still only does it occasionally. So, obviously, there's some iron in there....but

...that leads me to my questions (1) how can something with such a tiny amount of iron make something this magnetic? (see the video below), and (2) what kind of rock is it in general?

Would love any help in clearing up my mystery. Thanks! Oh, and size-wise, you should be able to tell by the comparison to the tip of the pen, but it's about an inch across.







And a little movie so you can see the amount of magnetism:

 

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[DirtManicure]

Hi Dougie, I’m a newb but been a rock hoarder for as long as I’ve had pockets.
Appearance alone I’d say it’s jasper, but hard to tell without a little higher resolution. Sounds like jasper, too if that makes sense.
My 2nd guess would be hematite, everybody will say it’s heavy because of the iron but when it’s blended or the iron isn’t in dense form it’s actually pretty light (think of a giant lump of rust... still iron, just fluffy.)
Does it have any chatoyance (shiny on the inside)? If you buffed it up would it look like wax or glass? If it looks like it’s been melted it could be the unicorn of rocks... starts with M and everybody thinks every black rock is one.
I could be totally in left field too but those are my quick hits.

 

[Dougie Webb]

Hi Dougie, I’m a newb but been a rock hoarder for as long as I’ve had pockets.
Appearance alone I’d say it’s jasper, but hard to tell without a little higher resolution. Sounds like jasper, too if that makes sense.
My 2nd guess would be hematite, everybody will say it’s heavy because of the iron but when it’s blended or the iron isn’t in dense form it’s actually pretty light (think of a giant lump of rust... still iron, just fluffy.)
Does it have any chatoyance (shiny on the inside)? If you buffed it up would it look like wax or glass? If it looks like it’s been melted it could be the unicorn of rocks... starts with M and everybody thinks every black rock is one.
I could be totally in left field too but those are my quick hits.

I think you're probably right with jasper. I found this picture, which looks a lot like my rock and the hematite would explain the magnetism. It just seems weird, though, that a quantity of iron that small could attract a magnet but not set of a detector!

 

[DirtManicure]

Sometimes iron is tricky, rust is iron oxide, soak that in being at you get iron acetate, which I use to dye leather. Doesn’t make the leather magnetic but she’s iron just the same. Minerals are sneaky sometimes!

 

[Clay Diggins]

This comes from a banded iron formation (BIF). The bands alternate between jasper/chert and hematite. BIFs are one of the main sources of iron ore. This particular piece looks like it might be from the Michigan deposits or possibly from the Vermillion range in Nevada.

Here are some examples of BIFs:
http://www.jsjgeology.net/Banded-iron-formations.htm

 

[Dougie Webb]

This comes from a banded iron formation (BIF). The bands alternate between jasper/chert and hematite. BIFs are one of the main sources of iron ore. This particular piece looks like it might be from the Michigan deposits or possibly from the Vermillion range in Nevada.

Here are some examples of BIFs:
http://www.jsjgeology.net/Banded-iron-formations.htm

Wow, that's amazing! Thanks so much. I did some searching based on this and was pretty much able to identify where/when I got the rock. I went camping in Grand Canyon about five years ago and flew to Phoenix and drove up from there. This picture of banded red jasper looks just like mine and is from that same area of Arizona. How cool!