FMF - Friends of Minerals Forum, discussion and message board

[Amir Akhavan]

The easiest non-destructive way to test *colored* quartz varieties is dichroism.
Just rotate the specimen in front of a computer monitor or a polarizer filter and check for changes in color or hue.
Smoky quartz changes from a light reddish tone to darker yellow tones.
Check mindat's smoky quartz page to see an example.
One has to figure out the correct axis/angle to rotate the specimen.
On a crystal one would have to face the "long side" / c-axis, for cut stones and irregular pieces one has to play a bit.
Watch out: Lack of dichroism does not always mean glass, it just means "not smoky quartz" or "not citrine" or "not amethyst" etc.
But with something as big as the specimen in question it is usually quartz versus glass.
And of course, dichroism is the same for naturally and artificially irradiated specimens.

[stoned]

VERY interesting Amir, thank you! I shall try what you suggested soon. Of course being a newbie, I've never heard of dichroism. Should the monitor screen be white as in a blank page in a browser when I try this? I would think so.

[Amir Akhavan]

> Should the monitor screen be white as in a blank page in a browser when I try this?

yes
It won't work with one of these cathode ray tube monitors, of course, but everything else should work, including your smartphone.

[Duncan Miller]

[stoned]

I'm going to download that now Duncan, thanks.

I rotated it in front of my cell phone with bright white light. I didn't notice any red hues, but yellows yes. Interestingly, I have a clear quartz obelisk and did the same and it had very pale yellowish hues too, only when put up against the light. Is that normal?

[Amir Akhavan]

smoky quartz dichroism example
https://www.mindat.org/min-3689.html

[stoned]

Thanks Amir, great example photos. I have the Champagne color smoky quartz, I guess they call it. I see lots of yellow hues, and just now noticed red specks in areas after looking again.

I guess we can end the discussion on this piece above anyway. May have more gems to show down the road. I'm just glad it passed the test as real, or I would be contacting the seller, to get my $20 back! Which by the way I hope was a fair price for the piece above.