Identifying Modal Percentage in a Mineral Thin Section


This is my first time using this software. I was instructed by my supervisor to look into ImageJ software to identify different minerals present in a thin section. I’ve look at many videos and different application methods, but still having trouble with the threshold.

The thin sections I have are hawaiian basalts and comprise of plagioclase, pyroxenes, olivine, and vesicles. It is very hard to identify each mineral when plagioclase is half white and half black and blends in with the groundmass. Under cross polarized light, the same minerals have different colors and vesicles blend with ground mass. I have tried 8 to 36 bw bit and the color bit as well.

Is there any way to find out what the percentage of each mineral is in the picture with ease?

Here’s a sample of the thin section I would be working with. I need to find the percentage of vesicles, pyroxenes, plagioclase, and olivine.

Plane Polarized:

Cross Polarized:

Thank you for your time and help!

Hello Taykim i also want to learn Image J,kindly help me.

Hi Taykim, for this kind of analysis I would recommend software like MultiSpec (free, or ENVI (very expensive). Both do their jobs very well. I am not sure if you want to use crossed polarisers as the colors are not really reproducible. Better use b/w images made with different wavelengths, then let the software sort it out.

This is a simple example I made years ago from an iroe ore deposite withe mixed chamosite and magnetite, which is 11.7% for the magnetite class.

Remember that area% likely does not correspond to the real percentage unless you analyse a large number of different sections.