Earth Optics Video 6: Biaxial Minerals

[@EarthOpticsVideos]

Hi Everyone! Thank you so much for the feedback! I'd like to clarify some things about mineral 2. It is in fact a biaxial mineral. In uniaxial minerals, the 2V angle is equal to zero (there is only one optic axis), which is why we see a cross under the bertrand lens. The example here has a very low 2V angle (~15° or lower!), which is why it looks so similar to a uniaxial interference figure. You may notice that the the "elbows" of the isogyres (where each melatope is) don't exactly overlap and separate slightly upon rotation. Although it is faint, it is also possible to see some light pass between the melatopes in this video. I'm sorry this is a difficult example - I'll try to make some more videos with better quality examples and recordings in the future. Hope this helps!

[@rosesingha452]

plz make more videos on optical mineralogy ...like determining vibration direction of a anisotropic mineral

[@nadunansanayaka3708]

😄. I also think that is uniaxial

[@dematata2020]

Hello, i have a question about this, especially in a biotite.. in a book, there was said "some biotite is sensibly uniaxial..." does that mean biotite in a low 2V angle? and what in case biotite will be have a very low 2V angle? Basal section or parallel to the c axis section?

[@arpanbera1287]

In this whole discussion we located Y axis at NW-SE direction..why we didn't located it at NE-SW direction??as well as why we took SE quadrant for isgyre .we may take it NE quartdent

[@denisefayejaner4767]

The mineral that you used in the 2nd example is a uniaxial mineral.

[@azzamabdulhafidhaliahmed9624]

YES I AGREE WITH U

[@amannaainaniamirhamzah2030]

yes, so much more twrds uniaxial

[@EarthOpticsVideos]

Such a tricky example! I should have included a different grain in this video. It is actually a biaxial mineral with a very low 2V angle, which is easy to confuse for a uniaxial mineral. I explain this in a bit more detail in the comment above. Thanks for the useful feedback :D

[@kgolanekgotlelelomarota7682]

It's been 7 years since you commented this and so I wonder if you still believe it's uxiaxial or not..😅

[@ANILTIWARI-wu8hf]

Please help me answer for this question. If 2V = 180, the indicatrix will be? A. Biaxial positive B. Biaxial negative C. Uniaxial positive D. Uniaxial negative

[@rafiquemohammad5345]

confusion in uniaxial and biaxial minerals please clear it

[@aratighodke8720]

Thank you so much…🙏🏻

[@seapickle4484]

Thank you!!

[@anlamzao634]

Loved it!

[@federicomoroni2946]

why in the second example is biaxial? i would say it is uniaxial?! pretty confused

[@faisalmuhammad5364]

federico moroni You are right 2nd mineral is uniaxial where isogyres don't split into two while rotating the stage suggesting its an uniaxial

[@EarthOpticsVideos]

It is a biaxial mineral with a very low 2V angle - I've posted a more detailed explanation. Hope this helps!

[@NoraInuG]

Is the second example a mineral with a 2V angle of 1 degree?

[@EarthOpticsVideos]

It is certainly a very low 2V angle. In the video I mention that it could be between 15 and 30°. It is probably closer to 15° or lower. I've posted a detailed explanation - hope this helps!

[@Maaznotes]

Nice..keep it up

[@emrecaglan6421]

bruh