Pseudomorph of limonite after pyrite, Mayer, Arizona

&lt;p&gt;Pyrite forms perfect cubes that are bright and brassy. &amp;nbsp;Under certain conditions, groundwater carrying iron can, at depth, cause selective transformation of the iron sulfide of pyrite to hydrous iron oxide of limonite. &amp;nbsp;This takes place so delicately that the form of the pyrite cube is preserved, even though the composition changes from sulfide to oxide. &amp;nbsp;The product is called a pseudomorph, in this case of limonite after pyrite. &amp;nbsp;&lt;/p&gt;

Whereabouts

I am hazy on where I found this. I believe it was in the Mogollon Rim area near Mayer, Arizona, in country rock of Precambrian age (late Paleoproterozoic). I like the form of this, and the earthy hue, and the delicacy of the selective replacement over time.

Age & Formation

Unknown