Optical Mineralogy Pt.2- Optical Indicatrix, Uniaxial vs Biaxial, Interference Figures | GEO GIRL

Ever get to the optical indicatrix part of optical mineralogy and just close the book because it made no sense? Well this video covers how to use the optical indicatrix and its properties to identify minerals. How does the orientation of a mineral grain under thin section affect its optical properties? All minerals have an optical indicatrix, which is just a fancy word for an ellipsoid we use to simplify the mineral grain and its orientation compared to the light passing through it. We can use special lenses, such as the upper swing-in condensing lens and the Bertrand lens, on petrographic microscopes to tilt mineral grains under thin section to determine the optical indicatrix orientation. What can understanding the optical indicatrix do for us when identifying minerals? Well it can allow us to determine the optic axis or axes, the optic angle, the optic sign, and the interference figures of mineral and use these optical properties for identification. At the end of this video, we summarize all the diagnostic properties useful for identifying minerals that we have gone over in this mineralogy playlist of videos. Enjoy!

References: Earth Materials textbook: https://amzn.to/3l5xbSf
Color atlas of rocks & minerals in thin section: https://amzn.to/3JlbJDg

GEO GIRL Website: https://www.geogirlscience.com/ (visit my website to see all my courses, shop merch, learn more about me, and donate to support the channel if you'd like!)

0:00 Review & what this video will cover
2:17 How crystal system affects optical properties of minerals
4:28 Intro to optical indicatrix
5:15 The uniaxial optical indicatrix
7:12 Uniaxial optic axis
9:40 The biaxial indicatrix and optic axes
12:03 Biaxial optic angle and optic sign
12:33 How to apply this to minerals under thin section?
13:30 Bertrand lens & condensing lens
16:14 Uniaxial interference figures
17:33 Uniaxial flash figures
18:46 How to determine optic sign of uniaxial minerals
21:57 Biaxial interference figures
22:35 Biaxial optic angle or 2V angle
25:15 Acute bisectrix figure & obtuse bisectrix figures
26:18 Biaxial optic sign
27:57 Review (mineral identification chart)
29:52 Upcoming content (& NEW PLAYLIST!)
31:07 Bloopers!

Directly offset your carbon footprint with Wren: https://shrsl.com/3d0t2

Non-textbook books I recommend:
Oxygen by D. Canfield: https://amzn.to/3gffbCL
Brief history of Earth by A. Knoll: https://amzn.to/3w3hC1I
Life on young planet by A. Knoll: https://amzn.to/2RBMpny
Your inner fish by N. Shubin: https://amzn.to/3cpw3Wb
Oxygen by N. Lane: https://amzn.to/3z4FgwZ
Alien Oceans by K. Hand: https://amzn.to/3clMx1l

Tools I use as a geologist/teacher/student:
Geology field notebook: https://amzn.to/3lb6dJf
Geology rock hammer: https://amzn.to/3DZw8MA
Geological compass: https://amzn.to/3hfbdLu
Geological hand lens: https://amzn.to/3jXysM5
Camera: https://amzn.to/3l6fGRT
Carbon-neutral backpack: https://shrsl.com/3cvkc

Image sources:
https://4.bp.blogspot.com/-E3PN_Nk8ud...
https://amzn.to/3wWF2Wg
https://i.pinimg.com/474x/c8/f4/c0/c8...
https://amzn.to/3wWF2Wg
https://upload.wikimedia.org/wikipedi...
http://www.mtholyoke.edu/~mpeterso/cl...
https://www.researchgate.net/publicat...
https://www.wgtn.ac.nz/sgees/images/e...
https://image3.slideserve.com/6569585...
https://viva.pressbooks.pub/app/uploa...
https://amzn.to/3wWF2Wg
https://www.tulane.edu/~sanelson/imag...
https://viva.pressbooks.pub/app/uploa...
https://opengeology.org/Mineralogy/wp...
https://viva.pressbooks.pub/app/uploa...
https://opengeology.org/Mineralogy/wp...
https://opengeology.org/Mineralogy/wp...

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