There is no way you can reliably identify hand samples from 2-D images
posted on-line. I have tested myself with the images of ore sample
posted on the SEG Newsletter website and I have failed badly (ca. 60%
success rate). You could try it the other way around though and give the
students properties of a mineral (without showing pictures) and ask them
to identify it based on those properties (basically following a flow
chart and using their textbook or appropriate websites) or you can
combine the mineral picture with two or three additional properties
(e.g. hardness, density, reaction to HCl, magnetism etc.) to help them
The microscopy portion is much easier because microscopy is practically 2D so you can post pictures of thin sections in PPL and XPL (or RL if needed) and ask them to identify minerals based on that. You might need to show several XPL pictures to cover parallel vs inclined extinction or if you don’t have that give them this information.
I like to give my students comparison questions to test whether they are able to tell minerals apart that are easily confused (e.g. how would you distinguish magnetite from ilmenite (or augite from hornblende, etc.) a) in hand sample; b) under the microscope; give two properties they have in common and one in which they are different).
When I did mineralogy quizzes at Harvard, I would say:
"You can do one test. What would it be?" And then if the test was
destructive (or whatever), I would just tell them the answer. So, you
might set up some questions like:
Don’t forget Instagram, which is a platform almost all students are very familiar with and they can use from their phones, which they’re always looking at anyway! For those of you unfamiliar with Instagram, images and short videos are organized by hashtags. For example, I just checked and there are >17,000 images for #epidote alone! Just search for #thinsection or #petrography, or #petrology, and you will find many great pics, and of course many bad, useless pics. Many professional geologists post regularly, and with accurate captions. Check out @alexstrekeisen for a huge library of thin section pics, and @drrhcmadden for many megascopic images.