Mineralogists,

Most cinnabar I've seen has a bright scarlet to deep red color, but this mineral can also be silvery-gray (with no red at all) and everything in-between.  Seems a bit strange since this mineral has a pretty straightforward chemical formula.  Does anyone know what controls this variation?

Thanks!

Kent Ratajeski

Kent Ratajeski, Ph.D.
301 Slone Research Building
Department of Earth and Environmental Sciences
University of Kentucky
Lexington, KY 40506-0053

Phone:  859-257-4444
Fax: 859-323-1938
http://www.as.uky.edu/users/krata2

I was thinking in the same direction in as far as cinnabar is concerned. Similar mechanisms play a role in the color change of some silver minerals, such as proustite.

On the other hand variability in color occurs also on hematitic iron ores.

Pure hematite ores are in some cases dull brownish red, some are steel gray with a strong metallic luster, and even brilliant red hematite microcrystals occur.

In the case of hematite the cause of the various colors is situated in the domain of texture, crystal size, porosity, grain size and all kinds of physical aspects of the material.

AFAIK the chemical composition does not play a big role in this case, except if the ore  is not pure hematite, but rather a mixture of hematite, goethite and limonitic phases.

Or does someone have another explanation?

Greetings,

Rik Dillen -  mailto:rik.dillen@skynet.be rik.dillen@skynet.be
Mineralogische Kring Antwerpen -  http://www.minerant.org/ www.minerant.org

Lid worden van de MKA ?  http://www.minerant.org/MKA/lidworden.html www.minerant.org/MKA/lidworden.html

MINERANT - 4-5 mei 2024

Antwerp Expo

From: K. Royce via MSA-talk msa-talk@minlists.org
Sent: Sunday, June 4, 2023 18:57
To: Ratajeski, Kent kent.ratajeski@uky.edu
Cc: MSA-talk msa-talk@minlists.org
Subject: [MSA-talk] Re: what controls color in cinnabar?

Hi Kent,

I wrote a blog post about this actually: https://mineralcare.web.ox.ac.uk/article/cinnabar

Cinnabar is naturally red, but can undergo photo-oxidiation to form colloidal metallic mercury at the crystal surface. It's the mercury that gives it the silver coloration.

Hope this helps!

Kathryn

Kathryn Royce

D.Phil Candidate, University of Oxford

Email: kathryn.royce@ouce.ox.ac.uk mailto:kathryn.royce@ouce.ox.ac.uk

Web: http://mineralcare.web.ox.ac.uk http://mineralcare.web.ox.ac.uk/

       https://mineralcare.super.site/

LinkedIn: https://www.linkedin.com/in/kathrynroyce/

------- Original Message -------
On Friday, June 2nd, 2023 at 20:41, Ratajeski, Kent via MSA-talk <msa-talk@minlists.org mailto:msa-talk@minlists.org > wrote:

Mineralogists,

Most cinnabar I've seen has a bright scarlet to deep red color, but this mineral can also be silvery-gray (with no red at all) and everything in-between.  Seems a bit strange since this mineral has a pretty straightforward chemical formula.  Does anyone know what controls this variation?

Thanks!

Kent Ratajeski

Kent Ratajeski, Ph.D.
301 Slone Research Building
Department of Earth and Environmental Sciences
University of Kentucky
Lexington, KY 40506-0053

Phone:  859-257-4444
Fax: 859-323-1938
http://www.as.uky.edu/users/krata2

Hello,

As a cinnabar enthusiast and hunter of new mercury minerals, my compliments to the blog of Ms. Royce. The major studies are referenced and wonderfully summarized.

I have been to a large number of mercury mines. The color of cinnabar can vary from bright orange to nearly black across deposits. In my experience, cinnabar at volcanogenic mines is always more photoreactive than that found at carbonate-hosted mines. I also feel that exotic cinnabar colors are more often found at volcanogenic mines.

In addition to atomic chemistry causes, cinnabar can also change color depending on its grain size. This is an effect seen in the sub-micron range. It’s possible to change the color of vermillion pigment by controlling the grind. Orange colloidal cinnabar in silica is noteworthy at the McDermitt mine in Humboldt Co., Nevada, Manhattan mine near Clear Lake, CA, Kiggins mine near Portland, OR, and the Oriental mines near Chovar, Valencia, Spain. There are many others.

Cinnabar darkening and silvering impacts classical paintings. There is not just one cause of the darkening of classical art works, nor just one alteration product, and this also seems to be the case with natural mercury compounds found at mines. Setting aside the many compositional and structural causes of color, if there is any consistency with respect to darkened cinnabar that I have noticed, it is that the surface darkened or silvered by light exposure is often (but not always) a sub-micron layer that can be removed by abrasion.

I have personally witnessed color change in the field hundreds of times. It is curious that Nevada cinnabars nearly all darken in sunlight, and some in a matter of seconds, while Coast Range California cinnabars do not, or only do so very slowly. Again, the exception are volcanogenic California HgS deposits, such as at Clear Lake and the Manhattan mine nearby.

Of course, when it comes to minerals with mercury, nitrogen, and halogens, darkening should not be surprising. These mixture are basically a natural form of silver compounds used to make photographs, but with mercury being the dominant cation instead of silver. The chemistry of photographic film is discussed in this thesis: https://scholarcommons.sc.edu/cgi/viewcontent.cgi?article=1085 https://scholarcommons.sc.edu/cgi/viewcontent.cgi?article=1085&context=senior_theses#:~:text=Photographic%20paper%20and%20film%20consist,bromine%20is%20the%20most%20common &context=senior_theses#:~:text=Photographic%20paper%20and%20film%20consist,bromine%20is%20the%20most%20common.

Lastly, red orange terlinguacreekite (https://www.mindat.org/min-27470.html) from McDermitt darkens with light exposure. If the sample is them put away out of the light for several months, the original color returns. I sincerely hope that one day a competent lab might ascertain the mechanism for this color reversal. I believe it is possible that understanding terlinguacreekite color reversal might lead to a method to reverse cinnabar darkening in fine art works. BTW- I have washed massive New Almaden cinnabar in rust removers that turn it dark grey (nearly black). I was surprised to find the cinnabar reverted to its original color after being kept in the dark for some time, just like terlinguacreekite.

Fun!

Cheers,

Mike

Michael F. Cox

Vice President

New Almaden Quicksilver County Park Association

PO Box 124, New Almaden, CA 95042-0124

(408) 644-7848 (cell)

mailto:mercury_miner@netzero.net mercury_miner@netzero.net

mailto:mercury.miner@gmail.com mercury.miner@gmail.com

From: K. Royce via MSA-talk msa-talk@minlists.org
Sent: Sunday, June 4, 2023 9:57 AM
To: Ratajeski, Kent kent.ratajeski@uky.edu
Cc: MSA-talk msa-talk@minlists.org
Subject: [MSA-talk] Re: what controls color in cinnabar?

Hi Kent,

I wrote a blog post about this actually: https://mineralcare.web.ox.ac.uk/article/cinnabar

Cinnabar is naturally red, but can undergo photo-oxidiation to form colloidal metallic mercury at the crystal surface. It's the mercury that gives it the silver coloration.

Hope this helps!

Kathryn

Kathryn Royce

D.Phil Candidate, University of Oxford

Email: kathryn.royce@ouce.ox.ac.uk mailto:kathryn.royce@ouce.ox.ac.uk

Web: http://mineralcare.web.ox.ac.uk http://mineralcare.web.ox.ac.uk/

       https://mineralcare.super.site/

LinkedIn: https://www.linkedin.com/in/kathrynroyce/

------- Original Message -------
On Friday, June 2nd, 2023 at 20:41, Ratajeski, Kent via MSA-talk <msa-talk@minlists.org mailto:msa-talk@minlists.org > wrote:

Mineralogists,

Most cinnabar I've seen has a bright scarlet to deep red color, but this mineral can also be silvery-gray (with no red at all) and everything in-between.  Seems a bit strange since this mineral has a pretty straightforward chemical formula.  Does anyone know what controls this variation?

Thanks!

Kent Ratajeski

Kent Ratajeski, Ph.D.
301 Slone Research Building
Department of Earth and Environmental Sciences
University of Kentucky
Lexington, KY 40506-0053

Phone:  859-257-4444
Fax: 859-323-1938
http://www.as.uky.edu/users/krata2

Good morning,

It may be worth noting that a tenebrescent variety of sodalite called hackmanite exhibits a certain degree of reversible photsensitivity.

Freshly broken surfaces exhibit a brilliant magenta color, which typically fades to a dull grey within minutes.  Vredenburg (1904) described it thus, "The phenomenon is particularly brilliant when the rock is first broken in the field, and the large blocks of elæolite (some of which are over a yard wide) appear, on fracture, as if suffused with blood."  If the specimen is kept under fluorescent light or in darkness for several days, a purplish color returns, though it is generally darker, less red, and more subdued.

From a crystal chemical perspective, hackmanite relates to sodalite (ideally, Na8Al6Si6O24Cl2) through substitution of sulfur for chlorine, likely coupled with ferric iron substituting for aluminum.  This was suggested by Petersen (1983) as a basis for the photochemical behavior of hackmanite, and hackmanite that I analyzed from Mont Saint-Hilaire has a chemistry that is consistent with that substitution.

But the particulars of the mechanism are likely due not just to the presence of sulfur but of the presence of sulfur radicals.  In sodalite, [cid:image001.png@01D99794.2960E430]  radicals promote the characteristic blue color of the mineral, with the occasional presence of [cid:image002.png@01D99794.2960E430]  radicals that produce a yellow coloration.  In hackmanite, some combination of [cid:image003.png@01D99794.2960E430]  and [cid:image004.png@01D99794.2960E430] , which produce a red coloration, probably occur in combination with [cid:image002.png@01D99794.2960E430]  (and perhaps [cid:image001.png@01D99794.2960E430] ) to yield the purple color. (Clark & Cobbold, 1978; Gobeltz-Hautecoeur et al., 2002)  The photosensitivity then probably relates to electron transfer driven by absorption of light.

Being that cinnabar is sulfur-essential, it seems likely that there would be some inclusion of sulfur radicals in its structure, as well, which might explain observed photosensitive behavior in that species.

I hope that that is useful.

Regards,
Peter Tice
Math Teacher
Rivendell Academy
Orford, New Hampshire  03777

From: mercury_miner--- via MSA-talk msa-talk@minlists.org
Sent: Sunday, June 4, 2023 4:57 PM
To: 'K. Royce' kroyce@pm.me; 'Ratajeski, Kent' kent.ratajeski@uky.edu
Cc: 'MSA-talk' msa-talk@minlists.org
Subject: [MSA-talk] Re: what controls color in cinnabar?

[*This email is from an outside sender. Please be careful clicking on links and attachments.]
Hello,

As a cinnabar enthusiast and hunter of new mercury minerals, my compliments to the blog of Ms. Royce. The major studies are referenced and wonderfully summarized.

I have been to a large number of mercury mines. The color of cinnabar can vary from bright orange to nearly black across deposits. In my experience, cinnabar at volcanogenic mines is always more photoreactive than that found at carbonate-hosted mines. I also feel that exotic cinnabar colors are more often found at volcanogenic mines.

In addition to atomic chemistry causes, cinnabar can also change color depending on its grain size. This is an effect seen in the sub-micron range. It's possible to change the color of vermillion pigment by controlling the grind. Orange colloidal cinnabar in silica is noteworthy at the McDermitt mine in Humboldt Co., Nevada, Manhattan mine near Clear Lake, CA, Kiggins mine near Portland, OR, and the Oriental mines near Chovar, Valencia, Spain. There are many others.

Cinnabar darkening and silvering impacts classical paintings. There is not just one cause of the darkening of classical art works, nor just one alteration product, and this also seems to be the case with natural mercury compounds found at mines. Setting aside the many compositional and structural causes of color, if there is any consistency with respect to darkened cinnabar that I have noticed, it is that the surface darkened or silvered by light exposure is often (but not always) a sub-micron layer that can be removed by abrasion.

I have personally witnessed color change in the field hundreds of times. It is curious that Nevada cinnabars nearly all darken in sunlight, and some in a matter of seconds, while Coast Range California cinnabars do not, or only do so very slowly. Again, the exception are volcanogenic California HgS deposits, such as at Clear Lake and the Manhattan mine nearby.

Of course, when it comes to minerals with mercury, nitrogen, and halogens, darkening should not be surprising. These mixture are basically a natural form of silver compounds used to make photographs, but with mercury being the dominant cation instead of silver. The chemistry of photographic film is discussed in this thesis: https://scholarcommons.sc.edu/cgi/viewcontent.cgi?article=1085&context=senior_theses#:~:text=Photographic%20paper%20and%20film%20consist,bromine%20is%20the%20most%20common.

Lastly, red orange terlinguacreekite (https://www.mindat.org/min-27470.html) from McDermitt darkens with light exposure. If the sample is them put away out of the light for several months, the original color returns. I sincerely hope that one day a competent lab might ascertain the mechanism for this color reversal. I believe it is possible that understanding terlinguacreekite color reversal might lead to a method to reverse cinnabar darkening in fine art works. BTW- I have washed massive New Almaden cinnabar in rust removers that turn it dark grey (nearly black). I was surprised to find the cinnabar reverted to its original color after being kept in the dark for some time, just like terlinguacreekite.

Fun!

Cheers,

Mike

Michael F. Cox
Vice President
New Almaden Quicksilver County Park Association
PO Box 124, New Almaden, CA 95042-0124
(408) 644-7848 (cell)
mercury_miner@netzero.netmailto:mercury_miner@netzero.net
mercury.miner@gmail.commailto:mercury.miner@gmail.com

From: K. Royce via MSA-talk <msa-talk@minlists.orgmailto:msa-talk@minlists.org>
Sent: Sunday, June 4, 2023 9:57 AM
To: Ratajeski, Kent <kent.ratajeski@uky.edumailto:kent.ratajeski@uky.edu>
Cc: MSA-talk <msa-talk@minlists.orgmailto:msa-talk@minlists.org>
Subject: [MSA-talk] Re: what controls color in cinnabar?

Hi Kent,

I wrote a blog post about this actually: https://mineralcare.web.ox.ac.uk/article/cinnabar

Cinnabar is naturally red, but can undergo photo-oxidiation to form colloidal metallic mercury at the crystal surface. It's the mercury that gives it the silver coloration.

Hope this helps!
Kathryn

Kathryn Royce

D.Phil Candidate, University of Oxford

Email: kathryn.royce@ouce.ox.ac.ukmailto:kathryn.royce@ouce.ox.ac.uk

Web: http://mineralcare.web.ox.ac.ukhttp://mineralcare.web.ox.ac.uk/

       https://mineralcare.super.site/

LinkedIn: https://www.linkedin.com/in/kathrynroyce/

------- Original Message -------
On Friday, June 2nd, 2023 at 20:41, Ratajeski, Kent via MSA-talk <msa-talk@minlists.orgmailto:msa-talk@minlists.org> wrote:

Mineralogists,

Most cinnabar I've seen has a bright scarlet to deep red color, but this mineral can also be silvery-gray (with no red at all) and everything in-between.  Seems a bit strange since this mineral has a pretty straightforward chemical formula.  Does anyone know what controls this variation?

Thanks!

Kent Ratajeski

Kent Ratajeski, Ph.D.
301 Slone Research Building
Department of Earth and Environmental Sciences
University of Kentucky
Lexington, KY 40506-0053

Phone:  859-257-4444
Fax: 859-323-1938
http://www.as.uky.edu/users/krata2

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