I often find little pockets with a skin of pure iron oxide pigments in larger sandstones. Sometimes in boulders, too. This one looks bumpy in texture, though, and that’s what made it stand out to me. It looks like botryoidal hematite.
Of course, when I saw the rock I had to pry it out of the ground to take home with me. And this is why I can’t have nice nails.
Botryoidal Hematite
It takes millions of years for this mineral to form. Here at Wild Ozark, the ground is loaded with iron, and that is basically what makes hematite. It’s an iron oxide, just like many of the other pigment colors that I find here.
“Botryoidal” refers to the ‘grape-like’ appearance (the bumps). Dissolved iron in oxygenated ground water deposited the iron in that little gap in the stone, most likely when it was part of a larger rock and that gap was a space inside it.
Hematite makes a beautiful red pigment, but I’m not going to use this tiny piece for that. This is a specimen rock that I’ll keep in my studio for show-and-tell when visitors drop by.
The Colors in Our Rocks
Each color that make up the rocks here is due a different arrangement of elemental molecules that include iron oxides (red and orange), iron hydroxides (yellows), and sometimes include other elements like sulfur (yellows, black or gray) or manganese (purples, black, and browns) and calcium/magnesium (whites).
And the greenish mudstone/siltstone that I find is given its color by ferrous iron that formed under anaerobic conditions 300 some million years ago possibly during a landslide underwater.
