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Josele
Joined: 10 Apr 2012
Posts: 410
Location: Tarifa, Spain
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Posted: Nov 28, 2013 05:14 Post subject: Epitaxial rutile |
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Is generally accepted that rutile forming 60º angle orientation between crystals is due to epitaxial growth on hematite. But very often hematite is not visible in the specimen, as in this case.
An infinitesimal (not visible) quantity of hematite is enough to start epitaxy?
Can rutile grow like this without hematite at all?
Thanks for your comment.
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Rutile and siderite on quartz Alchuri, Shigar Valley, Skardu District, Pakistan 15 x 10 x 8 cm |
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Rutile and siderite on quartz Alchuri, Shigar Valley, Skardu District, Pakistan FOV: 7 cm |
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Rutile on quartz Alchuri, Shigar Valley, Skardu District, Pakistan FOV: 3 cm |
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John S. White
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Joined: 04 Sep 2006
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Location: Stewartstown, Pennsylvania, USA
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Posted: Nov 28, 2013 06:17 Post subject: Re: Epitaxial rutile |
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Very nice close-up in the third photo. This is not epitaxy. What you have is twinned rutile in a very common form, often referred to as reticulated or geniculated, and rutile of this habit is known as sagenite. Twinned rutile like this is typical on quartz but can also be found on other substrates, such as siderite. Here are two examples from my collection of such twinned rutile in quartz from Lavro do Cascalho, near Conselheiro Pena, Minas Gerais, Brazil. The smaller one is 4 cm across and the larger elongated one is nearly 11 cm. In the larger piece some of the rutile is entirely enclosed in quartz while much of it is not.
My guess is that this rutile is black because of a relatively high iron content, while your sample probably contains very little iron.
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Josele
Joined: 10 Apr 2012
Posts: 410
Location: Tarifa, Spain
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Posted: Nov 28, 2013 07:19 Post subject: Re: Epitaxial rutile |
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Thank you John, then I was confused about sagenite growth.
In accord with this, I suppose that angles between crystals and twin plane is 65º (as is in rutile sixlings), not 60º as in epitaxial rutile on hematite. Given that there is two twinning operation affecting the same crystal, can this be considered as a particular case of cyclic twinning?
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Rutile on and into quartz Alchuri, Shigar Valley, Skardu District, Pakistan FOV: 6 cm |
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John S. White
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Posted: Nov 28, 2013 08:39 Post subject: Re: Epitaxial rutile |
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In my earlier post I used the term geniculated incorrectly, for which I apologize. Geniculated twins are those that consist of just two components joined together like arm or leg bones at an angle.
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Martin Rich
Joined: 15 Aug 2013
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Location: Lower Austria
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Posted: Nov 28, 2013 15:27 Post subject: Re: Epitaxial rutile |
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An other possibility is a pseudomorph of Rutile after preexistent Ilmenite. Only a thought of myself.
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Pete Richards
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Posted: Nov 28, 2013 16:07 Post subject: Re: Epitaxial rutile |
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John S. White wrote: | ... This is not epitaxy. What you have is twinned rutile in a very common form, often referred to as reticulated ... |
Somehow, John and I have a knack for coming down on opposite sides of a theory! Josele is right to raise the question of the angles between crystals, which should not be 60° if these are twins. Martin Rich offers a good idea - that the precursor could have been ilmenite rather than hematite, since the ilmenite could supply the titanium to make the rutile.
I have little crystals from Mont Saint-Hilaire which look exactly like ilmenite plates, except that they are decorated with tri-directional lines just like sagenite, and often have projecting spikes of rutile. SEM-EDS shows that they contain no iron - only titanium and oxygen. These are oriented replacements of ilmenite by rutile that started out as epitactic associations, I believe.
I have also seen thick sagenitic mats of rutile embedded in vein quartz, and they clearly have a platy shape with well-defined edges. The surrounding quartz proves that this was the original shape of the aggregate. We have the same problem here as we have with cyclic twinning - if it is twinning, how does the rutile know how to stay in one plane as it twins, and fill out the well-defined shape but grow no farther? There are four equivalent and equally likely directions of twinning for rutile which define two planes at right angles to each other. A multiply twinned rutile should at least be composed of two intersecting sheets of needle-shaped crystals, and more likely should be a three-dimensional bush, not a planar disc.
I'm not prepared to say that sagenites NEVER form by twinning, though I find it difficult to see how it could happen. And in some cases, I believe we can infer that they form by oriented replacement of ilmenite or some other mineral.
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Rutile after ilmenite Poudrette Quarry, Mont Saint-Hilaire, Quebec, Canada crystals are about 1 mm across |
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Rutile after ilmenite Poudrette Quarry, Mont Saint-Hilaire, Quebec, Canada crystals are about 1 mm across Detail of first SEM image |
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Rutile after ilmenite Poudrette Quarry, Mont Saint-Hilaire, Quebec, Canada crystals are about 1 mm across |
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Rutile after ilmenite? Rowlandsville (now part of Philadelphia), Pennsylvania Rutile disc is about 2" across |
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_________________ Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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Jordi Fabre
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Joined: 07 Aug 2006
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Posted: Nov 28, 2013 16:38 Post subject: Re: Epitaxial rutile |
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More info: Ilmenite pseudo
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Josele
Joined: 10 Apr 2012
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Location: Tarifa, Spain
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Posted: Nov 28, 2013 18:49 Post subject: Re: Epitaxial rutile |
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Epitaxy, twinning, pseudomorphism... all together... Wow! this becomes more and more interesting!
From my naive ignorance I can think only about angles to determine if a sagenite is due to epitaxy or twinning. There is not much difference between 60 and 65º having in mind that nature tend to create divergences in theoretically parallel growth crystals.
Let me add some fuel to the fire with two simple observations:
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A is somewhat shorter than B and C, which are almost equal, conforming a more or less isosceles triangle little higher than the equilateral. To my understand, if is a twin, this triangle should be isosceles but slightly lower than equilateral. Pictures were taken perpendicular to sagenite plane. Measurements based on photos are not very reliable data but can be a clue. |
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This is supposed epitaxial rutile on hematite (or perhaps ilmenite pseudo after epitaxial rutile on hematite?) The triangle conformed by the three main directions is equilateral. Not absolutely reliable but... |
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Entire sample of previous photo Haramosh Mts., Skardu District, Pakistan 6 x 4,5 x 1,5 cm |
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marco campos-venuti
Joined: 09 Apr 2014
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Posted: Jul 17, 2014 12:19 Post subject: Re: Epitaxial rutile |
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Just some pictures of the famous star rutile quartz. In these samples crystallization starts with hematite crystal (iron oxide) and when iron finished, then start to crystallize the rutile (titanium oxide). The rutile is red to yellow because most of the iron was used in the hematite crystal.
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Star of rutile in quartz crystal Novo Horizonte, Bahia, Brazil A small hematite crystal lies at the center (6.5 cm) |
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Star of rutile in quartz crystal Novo Horizonte, Bahia, Brazil With hematite crystal at the center |
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Star rutile in quartz Novo Horizonte, Bahia, Brazil 25 mm, 30.3 cts |
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marco campos-venuti
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Posted: Jul 17, 2014 12:22 Post subject: Re: Epitaxial rutile |
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In this sample the rutile star grows along an elongated hematite.
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Star rutile in quartz Novo Horizonte, Bahia, Brazil 14 mm, 18.2 cts |
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top view of the same sample |
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marco campos-venuti
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Posted: Jul 17, 2014 12:26 Post subject: Re: Epitaxial rutile |
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This is sagenite. It is called green rutile. Just a little bit green, I don't know why. It is from an old deposit.
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Sagenite rutile in quartz Brazil 24 mm, 23.3 cts |
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marco campos-venuti
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Posted: Jul 17, 2014 12:28 Post subject: Re: Epitaxial rutile |
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An other sagenite, but a bit different. It is yellow and is composed of individual stars.
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Sagenite rutile in quartz Brazil 25 mm, 28.6 cts |
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Mark Ost
Joined: 18 Mar 2013
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Posted: Jul 17, 2014 20:00 Post subject: Re: Epitaxial rutile |
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Stunning examples Marco
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stef4412
Joined: 14 Apr 2013
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Posted: Jul 25, 2014 15:54 Post subject: Re: Epitaxial rutile |
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Josele wrote: | Epitaxy, twinning, pseudomorphism... all together... Wow! this becomes more and more interesting!
From my naive ignorance I can think only about angles to determine if a sagenite is due to epitaxy or twinning. There is not much difference between 60 and 65º having in mind that nature tend to create divergences in theoretically parallel growth crystals.
Let me add some fuel to the fire with two simple observations: |
In fact I think that crystals in your first photo are not twinned : some elements of the twin seems to be missing
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Josele
Joined: 10 Apr 2012
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Location: Tarifa, Spain
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Posted: Jul 25, 2014 16:24 Post subject: Re: Epitaxial rutile |
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More pics:
Mineral: | Rutile |
Locality: | Alchuri, Shigar District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FOV: 5 cm |
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35673 Time(s) |
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Josele
Joined: 10 Apr 2012
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Location: Tarifa, Spain
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Posted: Nov 25, 2021 10:27 Post subject: Epitaxial or twinned rutile? |
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I have not photomicrography equipment but recently I bough a mobile phone with microscope camera (30x). Depth of field is very short, focal length is fixed and there is no possibility of stacking photos. Even so, some shots are useful to observe details.
I took some photos of the same rutile in last photo and also of another one on hematite. What I see leads me to think about the possibility that epitaxy and twinning coexist in some sagenite nets. Maybe this is a common thing but I haven't read about it.
Comments are welcome, thanks for your interest.
Mineral: | Rutile |
Locality: | Alchuri, Shigar District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.0 mm |
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Contacts between needles are not perfectly encased elbows as we see in macro twins
Central diagonal needles are somewhat divergent, maybe one is epitactic and the other one twinned? |
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Mineral: | Rutile |
Locality: | Alchuri, Shigar District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.66 mm |
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Unconnected needles form about 60º angles while some small elbows above left at the photo are ≈65º |
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13527 Time(s) |
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Mineral: | Rutile |
Locality: | Alchuri, Shigar District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.66 mm |
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Vertical and oblique rutile are connected forming ≈65º angles |
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Mineral: | Rutile |
Locality: | Tormiq Valley, Baltistan District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.66 mm |
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Connected needles at the lower half of photo are at ≈65º while overlapped ones in the upper half form ≈60º anglesTwinning, epitaxy or both? |
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Mineral: | Rutile on hematite with muscovite |
Locality: | Alchuri, Shigar District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | 6 x 4.5 x 1.5 cm |
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Hematite with epitaxial rutile running perfectly parallel to its three crystallographic basal axes |
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Mineral: | Rutile |
Locality: | Tormiq Valley, Baltistan District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.5 cm |
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Macroscopically, rutile runs parallel to crystallographic axes forming ≈60º angles… |
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Mineral: | Rutile |
Locality: | Tormiq Valley, Baltistan District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.66 mm |
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…but microscopically most angles are ≈65º and elbows look like perfect twin joints |
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Mineral: | Rutile |
Locality: | Tormiq Valley, Baltistan District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.66 mm |
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Mineral: | Rutile |
Locality: | Tormiq Valley, Baltistan District, Gilgit-Baltistan (Northern Areas), Pakistan | |
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Dimensions: | FoV: 2.66 mm |
Description: |
Even staggered neat elbows at ≈65º
Epitaxy, twinning or a combination? |
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Eck Noch
Joined: 09 Jan 2021
Posts: 28
Location: California
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Posted: Nov 25, 2021 11:57 Post subject: Re: Epitaxial rutile |
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Here is a fun one taken of my self collected material from the Eclipse Mine, photomicrograh by Nathan Renfro. Proposed epitaxy of rutile on Anatase or Brookite.
Mineral: | Rutile |
Locality: | El Dorado County, California, USA | |
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Dimensions: | 3mm |
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Eck Noch
Joined: 09 Jan 2021
Posts: 28
Location: California
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Posted: Nov 25, 2021 12:18 Post subject: Re: Epitaxial rutile |
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Here is a sample of photos I took myself with my iPhone 6, these were all collected from the Eclipse Pocket at our Eclipse Mine. Here you can clearly make out the Anatase cores on some, and on others it is not visible... there are easily 5 different colors of rutile that came from this pocket.
Mineral: | Anatase, Rutile |
Locality: | El Dorado County, California, USA | |
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Dimensions: | 8mm |
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Mineral: | Anatase, Rutile, Chlorite |
Locality: | El Dorado County, California, USA | |
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Mineral: | Rutile |
Locality: | El Dorado County, California, USA | |
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Dimensions: | 9mm |
Description: |
I love the blonde color of this Rutile. Also from the Eclipse Pocket at the Eclipse Mine. Unknown core mineral. |
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Mineral: | Anatase, Rutile, Dolomite |
Locality: | El Dorado County, California, USA | |
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Dimensions: | 7mm |
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Two colors of rutile side by side. |
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Eck Noch
Joined: 09 Jan 2021
Posts: 28
Location: California
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Posted: Nov 25, 2021 12:33 Post subject: Re: Epitaxial rutile |
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Another photo micrograph by Nathan Renfro of material from the Eclipse Pocket.
Mineral: | Rutile on Quartz |
Locality: | El Dorado County, California, USA | |
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Photo Credit: Nathan Renfro |
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Bob Morgan
Joined: 18 Jan 2018
Posts: 229
Location: Savannah, Georgia
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Posted: Feb 27, 2022 18:28 Post subject: Re: Epitaxial rutile |
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If you want to explore rutile twinning there is an article that is above my pay grade:
Structural rationale for the occurrence of the elbow twins in cassiterite and rutile by Massimo Nespoli and Bernd Soignier in the Journal of Mineralogical and Petrological Sciences, Volume 110, pages 157-165, 2015.
It is theoretical and mathematical but has some interesting illustrations, and helps me appreciate that twinning is more complex than just simple twin planes.
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