We saw a lot of rocks and minerals on last month's field trip to Goldfield, NV. At the second stop, our f.t. leader had laid out a large collection of large rocks on pallets, one row for one area, one row for another. The pallets were then arranged, north to south, by the age of the rocks. I thought it was a great way of arranging the rocks, especially since we didn't have time to go see them all in the field!
Today's mineral from Goldfield is alunite, a trigonal, sometimes psuedo-cubic, anhydrous alumino-potassic sulfate. In this photo, it's a hydrothermal, hypogene alteration mineral replacing potassium feldspar in rhyolite.
Goldfield has some of the nicest alunite I've seen, with a classic pink color, although one can also find classic pink alunite at Alunite, Utah and other places.
More alunite, still pinkish, and showing its classic tabular crystal form.
If you see a mineral with this shape, think alunite. It's not always pink (or reddish); it can be colorless, white, gray, to yellowish. The supergene form is often massive, looking somewhat like jarosite.