Friday Rock Blogging: Zoned Feldspar

Potassium feldspar crystal zonation I found this one on the side of the road, near the top of Sonora Pass. The zoned structure reflects some change in the conditions under which the crystal was growing, but frankly, telling you that this is feldspar has strained my mineralogy skills to the limit. If we are going to get a lesson on the difference between normal and reverse zonation in alkali feldspars, it’ll have to come from some Gentle Reader who does real geology, and not this geophysics number-crunching bullshit with which I am so obsessed.


  1. darksociety wrote:


    We’re doing a lot of zoned plagioclase in my optics course, trying to figure out the An-Al% across the zonation. Of course, these are tiny, tiny grains compared to yours which dwarves a penny!

    Amazing stuff!

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