|MadSci Network: Earth Sciences|
Hi Dave, Metal oxides can take on quite a variety of colors, depending not only on the elements, but on the oxide's (microscopic) solid structure. The color of the oxide is seldom a sure way to identify a metal. Colors may be due to the electronic absorption spectrum of the compound (oxides are chemical compounds), or to interference between incoming and reflected light on thin oxide layers. I suppose your question relates to the colored layers formed on blank metal if you heat it e.g. in a flame. Purple reflections may be seen on iron under such conditions: this is due to interference. On the other hand, hematite, Fe2O3, as a fine powder, can serve as a purple pigment. Rust, and other corrosion products, are seldom pure oxides. Copper, on heating, can also take on purple hues: at certain temperatures, copper(I) oxide Cu2O, is stable. Best Regards Werner Sieber
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