Need a little help...

[kcm]

A friend on another forum posted this rock pic, and it's got everyone stumped!! It came from a farm field in the Rochester/Minneapolis area. He says it's somewhat soft, as scratching the dirt out caused scuffs. Don't know what he was scratching with. He also says the hole is about an inch across. Here's his pic:

 

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[Eu_citzen]

Get him to do a hardness test, a proper one, with a knife and copper penny. Also he should do an acid test for limestone. (determine the host-rock)

"The hole" looks like an impression left after a crystal weathered out, without finding a rock with the crystal still attached....We can only speculate.

 

[loco oro]

Looks like quartzite with vugs, looks as if there is points of crystals protruding from all sides of cavity, or vug

 

[IAMZIM]

The problem with it being quartzite is, that whole area is sandstone/limestone for hundreds of feet deep. I used to collect fossils in that area when I lived in Wisconsin and Minnesota. That is an unusual rock for that area, so, I'm thinking it had to be carried there glacially. Unless it IS limestone......then you have what looks like a octahedron crystal.... Very interesting rock.......

 

[loco oro]

When you have bedded sandstone, you are likely to have quartzite at the contact zones,being morphed sandstone, very cool in any case

 

[IAMZIM]

When you have bedded sandstone, you are likely to have quartzite at the contact zones,being morphed sandstone, very cool in any case

Gotcha, I learn something new every day!