Help with identification....

**mnflyfisher** · February 4th, 2013, 03:19 PM

HI there, I found this "rock" about 25 years ago in Southern Minnesota... I have not been able to find out what it is... can anyone assist? It is very shiny, almost Chrome looking and extremely heavy.

Thanks

Chuckphoto (2).JPG

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**Neverfly** · February 4th, 2013, 03:46 PM

Looks like blue pyrite...

**marnixR** · February 5th, 2013, 01:41 AM

looks like azurite to me

**John Galt** · February 5th, 2013, 02:25 AM

It's years, or decades since I've done any mineralogy, but this evoked the response stibnite. If you draw it across a ceramic material it should leave a streak. Does it do so?

**Neverfly** · February 5th, 2013, 02:42 AM

Originally Posted by John Galt

If you draw it across a ceramic material it should leave a streak. Does it do so?

This post allows a method of testing- excellent.

**John Galt** · February 5th, 2013, 03:57 AM

Originally Posted by John Galt

It's years, or decades since I've done any mineralogy, but this evoked the response stibnite. If you draw it across a ceramic material it should leave a streak. Does it do so?

It should also, if memory serves, feel greasy to the touch. Both are reflections of its very low hardness - only 2 or 3 on Moh's scale.

**scheherazade** · February 5th, 2013, 10:28 AM

Originally Posted by mnflyfisher

HI there, I found this "rock" about 25 years ago in Southern Minnesota... I have not been able to find out what it is... can anyone assist? It is very shiny, almost Chrome looking and extremely heavy.

Thanks

Chuckphoto (2).JPG

This link goes to a mineral table that might prove useful for your purposes. There are images of the minerals when you go to the home page of each.

Mineral Identification Key - Table IB

**Paleoichneum** · February 6th, 2013, 09:04 AM

Its a large chuck of massive galena. The cleavage planes and metallic coloring are distinct.

**marnixR** · February 6th, 2013, 11:30 AM

does galena show such a blue colour ? i would have thought it was more greyish metallic

**Neverfly** · February 6th, 2013, 12:26 PM

Originally Posted by Paleoichneum

The cleavage ...

You said cleavage.

**Paleoichneum** · February 6th, 2013, 02:02 PM

Originally Posted by marnixR

does galena show such a blue colour ? i would have thought it was more greyish metallic

It's dependent of the amount of oxidation on the surface, and also the quality and type of light that is reflecting off the cleavage faces from the window in the background. Also note that the crystal structure is clearly cubic (isometric) so azurite and stibnite are eliminated. Whereas the clearly silver-blue metallic coloration and distinct cleavage planes of the crystal eliminates pyrite as an option.

**Paleoichneum** · February 6th, 2013, 02:11 PM

0095554001350221181.jpg

note the isometric faces and blueish tinge dues to minute oxidation to smithsonite/hemimorphite on the faces. (Specimen can be viewed here http://www.mindat.org/photo-492604.html

**marnixR** · February 6th, 2013, 02:24 PM

fair enough, i relent in the face of your expertise - azurite was a mere layman's (and only slightly educated) guess, and i'm quite willing to amdit that i could be wrong

**Paleoichneum** · February 6th, 2013, 02:47 PM

its all good

**Flick Montana** · February 7th, 2013, 10:45 AM

I'd say galena. You say it is highly metallic and dense, so if it breaks into cubes when crushed, it's most likely galena.

That's a nice big sample, too. Good find.