Why no green quartz coloured by chromophore elements in nature ?

[cascaillou]

I was writing about synthetic quartz colored by doping when that question hit me.

I guess the answer might lie in the chemistry associated with specific geological settings...

I'm especially wondering about chromium. Green coloured chromium "doped" varieties are known for various silicate minerals such as Cr-Dravite, Cr-Diopside, Cr-tremolite, Cr-Beryl (emerald), etc.
However, despite quartz is found everywhere on the globe, and may form through a variety of genetic processes (most notably hydrothermal and pegmatitic), yet no green coloured Cr-bearing quartz was ever reported (I'm strictly talking of body color here, not about quartz coloured by inclusions).
Besides, unless reports of synthetic quartz coloured green by chromium doping are unfounded (that info seems confirmed but I couldn't actually locate an analysis report, so if you know of one please share), it seems that chromium incorporation would be compatible with a quartz lattice.

So, why, why, why...

[Stephen Challener]

I am only aware of green lab quartz colored by iron. Quartz doesn't really love to accept a lot of other elements happily into its lattice, though we do see a little bit of iron-colored green quartz in nature. In the lab we can generate environments that are a bit outside the typical possibility space geochemistry offers us (like having enough cobalt around to force it into the quartz lattice).

[cascaillou]

Thanks for the input. I had simultaneously asked the same question on mindat, if interested here are the answers: https://www.mindat.org/mesg-824349.html

One answer points in the same direction than what you implied, meaning that the quartz lattice won't readily accept chromium, and another answer pointed to a geological setting contradiction (Cr occuring in silicon poor rocks)

[Stephen Challener]

The geochemical answer is true in igneous magmas but not in ie metamorphic rocks. Chromium fractionates out of magmas first because it is highly compatible and silica fractionates out as one of the last, but that isn't the only way to generate chemical mixes on earth, and you can easily end up with situations where chromium occurs in silica-rich environments. It just doesn't go into the quartz.

[cascaillou]

thanks for teh explanations Stephen. That question was seriously bothering me

[steinfroilein]

Maybe following links shows you too the problem with chromium-doped quartz synthetic vs natural/irradiated green quartz

https://ggtl-lab.org/sites/default/file ... %2C-5p.pdf

https://hal.science/hal-00469711v1/file ... 20instance.

https://link.springer.com/article/10.10 ... separation.

https://grjapan.ddo.jp/gaaj_report/2006 ... -02en.html

https://grjapan.ddo.jp/gaaj_report/2006 ... Figure%201:

https://www.researchgate.net/publicatio ... een_Quartz

https://pubs.geoscienceworld.org/msa/am ... een-quartz

https://www.sciencedirect.com/science/a ... 6X25006875

[cascaillou]

Thanks for sharing those links