Is this gold?

July 4, 2008 12:30 PM

Is that gold I'm seeing in this hunk of quartz?

My girlfriend found the rock in Dawson City, Yukon while walking on the tailings of an old gold mine. I realize it's nowhere near pure, but amongst the grime and silvery metal, there is something metallic and gold coloured.

I know that veins of gold are found in quartz, and I'm fairly sure this is a hunk of quartz. The next picture in the album is the reverse side of the rock.

If it's not gold, what mineral/metal is it?

posted by Brodiggitty to science & nature (18 answers total)

Iron pyrite?
posted by fire&wings at 12:35 PM on July 4, 2008

IANAM(inerologist), but I have several VERY similar attractive chunks of quartz from Northern Quebec in my garden. It's Iron pyrite, also known as "fool's gold" because lots of early pioneers went absolutely apey over the "gold" and were sore disappointed.

This is semi-anecdotal, obviously, but as far as I can tell the pyrite-laden quartz I own is identical to the picture you've provided.
posted by Shepherd at 12:40 PM on July 4, 2008

Try to spark it...if it does..."fools gold".
posted by hal_c_on at 12:55 PM on July 4, 2008

Looks like pyrite to me.
posted by arnicae at 1:07 PM on July 4, 2008

How does one "spark" a rock? Do you mean bash it against another rock like a caveman trying to start a fire?
posted by Brodiggitty at 1:07 PM on July 4, 2008

Drag the "gold" against uneven porcelain — flip a plate or a tile. If the streak is dark greenish and smells of sulfur, it's pyrite.
posted by stereo at 1:14 PM on July 4, 2008

Looks like it's pyrite. Thanks folks!
posted by Brodiggitty at 1:29 PM on July 4, 2008

Can you actually give us better pictures of it? I'm going to go against the grain and say that it isn't pyrite, but actually mica. Mica is commonly found in quartz.
posted by MaryDellamorte at 1:35 PM on July 4, 2008

It's probably both mica and pyrite inclusions (the rust stains give away the pyrite).
posted by vers at 1:49 PM on July 4, 2008

I'm a grad student in geology. Doesn't look like gold to me; from the picture, it looks like Muscovite (a white mica) with some iron staining around it. The picture isn't great, but fortunately for you there are a number of ways for you to test what you've got.

Here' why it looks like mica to me: First of all, the crystal habit, or shape, is incorrect. Mica has a sheet-like cleavage, and from the picture, that looks to fit the bill pretty well. Take a fingernail and see if you can pull off a few 'flakes' of the mineral in question. If you can pull some of it off, and clear-pale yellow flakes come off, you almost certainly have mica.

If it isn't flaky, try and scratch it with a nail. If you can scratch the mineral, you aren't dealing with Pyrite. Pyrite is harder than a metal. Unfortunately, scratching it with a nail means you could have either mica or gold-both are soft.

But honestly, to me it looks a lot like Muscovite.
posted by HighTechUnderpants at 2:01 PM on July 4, 2008

Thanks HighTech, you said it in much better words than I ever could.
posted by MaryDellamorte at 2:03 PM on July 4, 2008

The rust staining could be from pyrite, but it could be from another iron bearing mineral, too-biotite, hornblende, some pyroxenes...Those minerals don't appear to be in your rock, but your rock had to come from somewhere, and who knows what minerals were adjacent to your rock? If there are small, roughly equant, metallic looking grains, and the rust stains are concentrated around them, than that is likely pyrite. But the rust could be from a number of phases.
posted by HighTechUnderpants at 2:26 PM on July 4, 2008

Ugh. 'Pyrite is harder than most metals' not 'harder than a metal'. Sheesh.
posted by HighTechUnderpants at 2:29 PM on July 4, 2008

Ok. When I scratch it with a nail it comes off on my fingers like a very fine sparkly dust. Would that make it Mica?

Mica was what the guy at the gold panning tour told us to watch out for. He told us Mica is used in gold paint and other craft supplies. Also, when you looked at the river sediment in still, shallow water you could see "sparkles" catching the sun.

I'm uploading more pictures of the rock and the dust on my fingers. I wish I had a macro lens.
posted by Brodiggitty at 2:42 PM on July 4, 2008

Here's the dust.

Another shot of the rock in bright sunlight. Although I don't think it is much clearer than the last.
posted by Brodiggitty at 2:50 PM on July 4, 2008

Yeah. The fact that it came off as 'sparkly dust' means it is almost certainly mica. It broke off as small, flat flakes-glitter, basically.

If it was pyrite, it wouldn't scratch. If it was gold, it would scratch, but not flake off.

Muscovite, a type of mica.
posted by HighTechUnderpants at 2:58 PM on July 4, 2008

That's definitely mica.
posted by MaryDellamorte at 2:59 PM on July 4, 2008

Thanks everyone. I guess I am the proud new owner of a sparkly paperweight.
posted by Brodiggitty at 3:06 PM on July 4, 2008