Hi, Thanks for the tutorial. It is very easy to follow. May I please ask what the name of the honey-brown mineral to close to the amphibole at 1.0 minute? It the same colour under PPL and XPL.
Wow, that's a good question. I'm not positive, but I think it's a flake of biotite approximately parallel to the plane of the thin section. When biotite flakes are oriented parallel to the thin section (so, the c-axis is pointing up out of the section), they don't have the typical higher order interference colors that you see when the plane of the section cuts across their cleavage. I would have to scan around that thin section to find other grains in other orientations to be sure. I'm afraid I don't know much about where that rock comes from because I didn't collect it.
Probably the most definitive images are for elongate minerals where the c-axis (the long axis) lies in the plane of the thin section. In these cases, hornblende definitely shows inclined extinction. I agree it's not always so obvious in other orientations.
Really helpful. Keep up the good work. A small suggestion tho. Can you please put a cursor at the mineral of interest. Will be really helpful for beginners
Thanks for this comment. It turns out to be rather difficult to add pointers on a spinning image (easy with a stationary image), at least with the software that I use for video processing. I'll keep looking for a solution though because I agree it would be helpful.
@@mattkohn7819 Hello Sir, I would suggest the same as a pointer or cursor would help a lot especially for students like us whose professors don't teach well in class. Huge respect for your efforts! Love from India!
Good morning All your thin sections have equal thickness? And how is this thickness? I ask incl. because I'm wondering why yours hornblendes one time have yellow colours and other time blue colours?
Hi Jozef, yes the sections are all 30 microns thick (or very nearly). The differences in interference color reflect either different compositions, or different orientations, or both. Exactly what colors you see depends on the shape of the optical indicatrix (how spherical, flattened, or elongate) and how the section happens to cut through that (orientation of the crystal with respect to the plane of the thin section). Different composition hornblendes can have differently-shaped indicatrices. And different sections through the indicatrix can be more circular or more elongate. I hope this helps - if not, let me know and I'll comment more.
Hi, Thanks for the tutorial. It is very easy to follow. May I please ask what the name of the honey-brown mineral to close to the amphibole at 1.0 minute? It the same colour under PPL and XPL.
Wow, that's a good question. I'm not positive, but I think it's a flake of biotite approximately parallel to the plane of the thin section. When biotite flakes are oriented parallel to the thin section (so, the c-axis is pointing up out of the section), they don't have the typical higher order interference colors that you see when the plane of the section cuts across their cleavage. I would have to scan around that thin section to find other grains in other orientations to be sure. I'm afraid I don't know much about where that rock comes from because I didn't collect it.
Hello,
Thanks for your video, It is very helpful. My question is, Is it actually inclined extinction because I see parallel or symmetrical extinction.
Probably the most definitive images are for elongate minerals where the c-axis (the long axis) lies in the plane of the thin section. In these cases, hornblende definitely shows inclined extinction. I agree it's not always so obvious in other orientations.
Really helpful. Keep up the good work. A small suggestion tho. Can you please put a cursor at the mineral of interest. Will be really helpful for beginners
Thanks for this comment. It turns out to be rather difficult to add pointers on a spinning image (easy with a stationary image), at least with the software that I use for video processing. I'll keep looking for a solution though because I agree it would be helpful.
@@mattkohn7819 you're welcome. You can add the cursor at a stationary image in the beginning and then show the rotating slide
@@dingdong1a_ Thanks - I'll experiment this semester.
@@mattkohn7819 thanks to you😊
@@mattkohn7819 Hello Sir, I would suggest the same as a pointer or cursor would help a lot especially for students like us whose professors don't teach well in class. Huge respect for your efforts! Love from India!
Good morning
All your thin sections have equal thickness?
And how is this thickness?
I ask incl. because I'm wondering why yours hornblendes one time have yellow colours and other time blue colours?
Hi Jozef, yes the sections are all 30 microns thick (or very nearly). The differences in interference color reflect either different compositions, or different orientations, or both. Exactly what colors you see depends on the shape of the optical indicatrix (how spherical, flattened, or elongate) and how the section happens to cut through that (orientation of the crystal with respect to the plane of the thin section). Different composition hornblendes can have differently-shaped indicatrices. And different sections through the indicatrix can be more circular or more elongate. I hope this helps - if not, let me know and I'll comment more.
❤🎉😮