Granite in thin section. All that white is a number of different minerals.
And this is what we call 'tartan twinning' :)
The best bit is the way those stripes change from black to white as you rotate it. Really very pretty.
One unexpected thing that all this microscope work has taught me is the extent to which I have right eye dominance. Keep both eyes open and look through the microscope with my right eye; no problem, I see a lovely field of crystals. Keep both eyes open and look through the microscope with my left eye; hahahaha. I can see a bit of microscope and some table.
I wonder how hard that is to change?