Smectite zones are primarily composed of smectite minerals, which are a group of clay minerals. These typically form in areas where rocks undergo weathering and are rich in aluminum and iron.

Ferruginous zones are areas that contain a high concentration of iron minerals. These can include various iron oxides and hydroxides, such as goethite, hematite, and limonite.

Limonite is a specific iron mineral, mainly made up of iron hydroxides. It forms through the weathering of other iron-rich minerals, and it's often found in ferruginous zones.

So, to answer your question: limonite can indeed be part of a ferruginous zone, since this type of zone is characterized by iron-rich minerals, which include limonite. However, limonite itself isn’t a separate zone but rather a specific mineral that can be found within these broader ferruginous zones. ;)

Bekhruz Oganiyozov Thank you so much, I really appreciate your reply - that really clears up ambiguity. I had a follow-up question if you're able to answer: is limonite a separate mineral from goethite and hematite (your response suggests that it's a separate ore, but I've seen sources online that refer to limonite containing goethite)? Thank you again.

Alyssa Ishchenko

I guess:

Limonite is not a distinct mineral but rather a general term for an amorphous mixture of hydrated iron oxides, primarily goethite (FeO(OH)) and other iron-bearing phases like lepidocrocite. It often forms as a weathering product of iron-rich minerals, including hematite and magnetite.

Since limonite lacks a definite chemical formula and crystalline structure, it is classified as a "mineraloid" rather than a true mineral. In older sources, it was sometimes considered a separate mineral, but modern classifications emphasize that it’s a mixture, predominantly composed of goethite. That’s why you’ll often find references to limonite “containing goethite.”

Finally:

Goethite (FeO(OH)) – A well-defined mineral with a crystalline structure.

Hematite (Fe₂O₃) – Another well-defined mineral, often a precursor to limonite through weathering.

Limonite – A general term for hydrated iron oxides, mostly composed of goethite but lacking a strict structure.

Bekhruz Oganiyozov Thank you so much for the help! This was very comprehensive