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Identity HelpSmoky Quartzsite with Inclusions?

12th Dec 2018 21:05 UTCRobert Darabos

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Curious if any one has seen rock / mineral like this before. It is a very common mineral in Michigan (even sold at local landscape and rock suppliers). It appears to be a Smoky Quartzsite with little Iron or Hematite stains/marks (they are in the material, definitely do not wash or rub off).


Any idea what the marks could be? It is not magnetic.


How would you describe the specimen?


I thought a Smoky Quartzsite with Iron/Hematite Inclusions



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13th Dec 2018 01:06 UTCPaul Brandes 🌟 Manager

Typical quartzite is this darker colour as it is rare to find a pure white quartzite (often called orthoquartzite). Remember that quartzite is nothing but metamorphosed quartz sandstone. Depending on what was cementing the quartz grains together originally, those cements can migrate and recrystallise during metamorphosis and produce pods and streaks. It appears that the red spots you see in this sample is the result of this process. The red spots are probably iron oxide, but would need to be analysed to be sure.

13th Dec 2018 07:07 UTCGregg Little 🌟

Hi Paul;

I suppose pure white quartzite is rare in continental sense but you should check out the hills/mountains of pure white quartzite on Manitoulin Island and adjacent Killarney Provincial Park in Ontario, Canada. In this local it is anything but rare being 1000's of feet thick. It is part of the Lorraine Formation and was deposited on the coastal region of proto-continent, now the Canadian Shield, soon after the earth's atmosphere rapidly became oxygenated around 2.2(?) billion years ago. Walking around a bare, bright white outcrop is blinding on sunny days.

14th Dec 2018 03:54 UTCPaul Brandes 🌟 Manager

I'm definitely aware of the white quartzites at Killarney, Gregg. I have samples from near there that were made into thin sections because they are so clean, and the fact you just don't see quartzite that pure in many places on Earth.

14th Dec 2018 18:24 UTCDonald B Peck Expert

Some of those red spots seem to be almost square. Could they be from oxidized pyrite cubes?
 
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