Explain mineral transparency, focusing on opaque minerals and how they are identified under a petrographic microscope
Understand the Problem
The provided text describes mineral transparency, focusing on opaque minerals and how they are identified under a petrographic microscope. It explains that opaque minerals appear black regardless of stage rotation because light cannot pass through them. Examples of opaque minerals include sulphides (like pyrite and chalcopyrite), oxides (like magnetite and hematite), ilmenite, and graphite. If a mineral is not totally black, it is not opaque and light passes through it.
Answer
Opaque minerals appear totally black and block all light, examples include pyrite, magnetite and graphite.
A mineral is considered opaque if it appears totally black and remains black regardless of the rotation of the microscope stage. Light cannot pass through opaque minerals. Examples include sulfides like pyrite and chalcopyrite, oxides like magnetite, hematite and ilmenite, and graphite.
Answer for screen readers
A mineral is considered opaque if it appears totally black and remains black regardless of the rotation of the microscope stage. Light cannot pass through opaque minerals. Examples include sulfides like pyrite and chalcopyrite, oxides like magnetite, hematite and ilmenite, and graphite.
More Information
Opaque minerals require reflected light microscopy for identification, unlike transparent minerals which are studied using transmitted light in petrographic microscopes.
Tips
A common mistake is to assume any dark-colored mineral is opaque. However, thin sections of even dark minerals can transmit some light if they are not opaque.
Sources
- 2.6 Properties Under Plane Polarized Light – Introduction to Petrology - viva.pressbooks.pub
- 2.6: Properties Under Plane Polarized Light - Geosciences LibreTexts - geo.libretexts.org
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