Mineral Polymorphism & PT Diagrams- Mineralogy | GEO GIRL

[@GEOGIRL]

Hi all, CORRECTION! -> Andalusite, Kyanite, and Sillimanite (Al2SiO5) are aluminosilicates, not technically feldspars, which are tectosilicates. Feldspars include the Plagioclase feldspar solid solution series: albite (NaAlSi3O8) - anorthite (CaAl2Si3O8) and the K-spar polymorphs: Microcline, Orthoclase, and Sanidine (KAlSi3O8). Sorry about the confusion! :D Another CORRECTION: aragonite is orthorhombic not rhombohedral, sorry about the mix up😉

[@Earthgazer]

Commenting in hopes that it helps the KZbin algorithm get you views! Very grateful you've created this channel

[@GEOGIRL]

Haha! I absolutely love it, thank you! ;D

[@JoesFirewoodVideos]

Rachel you’re in my top 10 of KZbin creators. I just find your content so interesting and enjoy learning cool stuff from you. I ❤️GEO GIRL

[@JoesFirewoodVideos]

22:38 of watch time.

I really like your videos! I am a geologist myself woking in the field, mainly in mining exploration! It's nice to rediscover old subjects I learned about so long ago or often learn for the first time! Excited to see what's to come! Also... super firendly comment: I don't think Kyanite-andalousite-sillimanite classify as feldspar... I've always called them aluminosilicates and upon reading wikipedia articles (lol), they classify as nesosilicates, as opposed to tectosilicates for feldspar! :) Really hope your channel grows! Like you mentionned, there is not much geology on KZbin so I'm glad I found your videos!

[@GEOGIRL]

Oh my gosh, you're right I was just going by my (apparently out of date) book, surprised I didn't catch that since I even said their composition out loud lol🤣 Well at least they have a similar composition to feldspar haha, I will pin a comment to make sure people know, thanks for pointing this out!! Also, so glad you like my channel! I love it when geologists watch my videos so that I can have validation that what I am saying is correct, and those times that it isn't they can point it out just as you did, so thank you again lol. Also, I agree that it is nice to review topics I learned so long ago, that's another reason I love making these videos, I can look back and remember these concepts after I have forgotten them haha :)

[@1forphotos861]

i regularly watch your videos. Its very very useful for my upcoming entrance. I love u Rachel.

[@GEOGIRL]

Glad you like them! :D

[@soumyaranjanmohanty9080]

How interestingly you are teaching. Respect Mam🙏

[@briancurtis6022]

Hi! This subject is very interesting to me. I was wondering about the conversion of unstable polymorphs to their more stable forms--such as stishovite or coesite changing to alpha/beta quartz, for example. Is this immediate upon transport to the new environment? Would stishovite immediately 'morph' to alpha quartz in surface-temperature conditions, or is it a gradual process with a measured rate? Or is it a probability situation, as with radioactive decay? Thanks.

[@geetapodili7375]

i think i heard that aragonite crytallizes in orthorhomic crystal system which is not matching with 18:00. am i wrong?

[@GEOGIRL]

Nope, you are 100% right! I don’t know why I put rhombohedral honestly haha cuz I’ve always known aragonite as orthorhombic, must have been a brain malfunction on my part, my bad. Thanks for catching this! I’ll add a correction comment ;) There are rhombohedral calcium carbonate polymorphism out there but aragonite is not one of them :)

[@geetapodili7375]

@@GEOGIRL Oh cool! And also i read that calcite crystalizes in trigonal/rhombohedral which is a part of hexagonal family. Are trigonal and rhombohedral systems the same? Btw loving your channel! I am actually enjoying the concepts which i used to previously find very hard, and everyday im looking forward to have fun learning with your videos. So thanks a whole lot for that. You are truly a beautiful Gem!!

[@GEOGIRL]

@@geetapodili7375 Thank you so much for the kind words!

[@geetapodili7375]

@@GEOGIRL Ahh! i think i understand it. Breaking down the crystal system into two lattice systems, rhombohedral and hexagonal. and thats why it is sometimes grouped under hexagonal system .and i too think there are too many definations and no clear distinction towards them . Totally appreciating the elaborate answer. it sure did helped me.. 😊

[@deepakkolli8422]

Hi You mentioned low quartz is hexagonal. But I found it is trigonal from various papers and journals. And could you also explain how these transformations take place?

[@GEOGIRL]

Well it seems you are right! Thanks for pointing that out. The book I am using says hexagonal, but when I look in the more recent papers, it says trigonal, so good catch! :) As for how these transformations occur, that would be by changing the temperature, the pressure, or both. As for what exact temperature/pressure these transitions occur at, it is different for every system of polymorphs and for every pair of polymorphs within a system, which is why the labeled PT diagrams are helpful. For example looking at the Quartz diagram we can tell exactly where (what P and T) the transition from low to high quartz (or vice versa) will occur. However, if you are referring to the exact mechanism that changes the T and/or P, that would also be different for every system. For example, calcium carbonate might switch from one polymorph to the other as its depth in the water column or sediment changed. However, with quartz, it would most likely be in a subsurface, high T environment, for example, within a melt rising from the mantle into a lithospheric magma chamber. The rising melt is decreasing in pressure, potentially causing it to convert from stishovite to coesite, then it starts to cool in T and crystallize, potentially causing it to convert to low quartz. However, later on if that solidified piece of low quartz ever became metamorphosed (heated and pressurized but not fully melted), it might convert back to one of the high pressure polymorphs during the metamorphism. Hope that helps a bit ;)

[@UsmanAli-yz5zc]

You are precious gem in Geology 🥰

[@GEOGIRL]

Thank you! :D

[@UsmanAli-yz5zc]

@@GEOGIRL Welcome,D

[@UsmanAli-yz5zc]

@@GEOGIRL How are you???

[@mohsenalshagdari1686]

Great. Thanks for your efforts. I hope the upcoming vedio regarding the geochemistry of travertine.

[@GEOGIRL]

Ooh, good idea, thank you! ;)

[@lanetPulse101]

Respect from India 🎉

[@almotalebahmed4432]

Thanks dr

[@GabrielMercier-ue9gs]

How can you show us pictures of rocks that are supposed to exist only at very hich T or P? Do you have superpowers that allow you to dive deep into the crust? I would not be surprised. However, I think it has to do with the way it is brought back to surface conditions, a bit like glass being obtained when you cool something to fast that it has no time to cristallize, or a bit like the difference between basalt and gabbro, or the difference beetween granite and ryolithe. Why doesnt all diamond turn back to graphite before it reaches the surface?

[@mathstube-mk4yq]

Thanks for the video 😃

[@GEOGIRL]

Of course! :)

[@theantattor6003]

and what's paramorph? Calcite is paramrphism of aragonite? Am i true?

[@GEOGIRL]

Yes, paramorphs are basically what we call a mineral that has formed via conversion of one polymorph into another (so like the actual representation of polymorph is paramorph) I hope that makes sense. In practice, I here more people use the term polymorph than paramorph so I am sure the technical usage doesn't matter that much haha :)

[@theantattor6003]

@@GEOGIRL thx you...now I know what I have confused.

[@mohsenalshagdari1686]

I am managing channel on telegram over 1800 geologist. Great to show them and invite them here 🙂.

[@GEOGIRL]

That's awesome, good for you! And thanks so much, I am so glad my videos can help in any way :D

[@oliverweeweepie3132]

Hi Nike

[@GEOGIRL]

She's a sweetheart ;)

[@vogliofinireluniversita4558]

Tvb