FMF - Friends of Minerals Forum, discussion and message board

[Marco Sr.]

I recently purchased some petrified wood pieces from Indonesia and was amazed by the vivid colors that I could see in the pieces with my microscope. I’m curious what minerals caused the different colors. I see on the web that a number of different minerals can cause the same colors like cobalt, chrome and copper can cause green and blue and carbon and magnesium oxide can cause black. Is there a way to visually tell which minerals caused the colors in these pieces from the pictures? What minerals can you see in the pictures?

[alfredo]

Reds and yellows in rocks are usually - in fact almost always - produced by various iron oxides, hematite for the red and goethite (mostly) for the yellow.

At a very small number of localities one might get other coloring agents, like cinnabar or cuprite for red, or orpiment or uranium minerals for yellow, but normally one is safe in assuming that those colors are due to iron oxides.

Anyway, it's a beautiful piece you got. Thanks to iron, and the oxygen in our atmosphere, Nature is more colorful that it would otherwise be. Well, I guess we should thank plants, for photosynthesis, without which we wouldn't have the oxygen.

[Marco Sr.]

[alfredo]

Orange is probably goethite too, and brown is probably various iron oxides mixed together.

Greens and blues, unless there are copper, nickel or chromium deposits around there, are probably also caused by iron! When ferrous and ferric iron both occur together in minerals (ie, iron in two different oxidation states), green or blue colors can result.

[Marco Sr.]