Palagonite
Hydrated, altered basaltic (mafic) volcanic glass
A yellow-brown alteration material formed when basaltic volcanic glass reacts with water, common in hydrovolcanic tuffs and pillow lavas.
- Mohs hardness
- Variable, roughly 3-5
- Color
- Yellow-brown, orange-brown to reddish or olive
- Type
- igneous
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Overview
Palagonite is not a single mineral but an alteration product: it forms when basaltic glass (sideromelane) reacts with water and devitrifies, producing a hydrated, gel-like to crystalline material rich in clays, zeolites, and iron oxides.
It is typically yellow-brown, orange, or reddish and gives palagonite tuffs their characteristic warm color. The material can be amorphous ("gel-palagonite") or partly crystalline ("fibro-palagonite").
Palagonite is of strong interest in planetary science because palagonitic soils on Earth are used as spectral and chemical analogs for the altered basaltic surface of Mars.
Formation & geology
Palagonite forms by hydration and chemical alteration of fresh basaltic glass, especially where hot lava interacts with water — in subglacial eruptions, shallow-marine pillow lavas, and explosive hydrovolcanic (phreatomagmatic) eruptions that produce glassy ash.
Water leaches and reorganizes the glass, releasing ions and crystallizing secondary clays (smectite), zeolites, and iron oxyhydroxides. Over time loose glassy tuff is cemented into hard, yellow-brown palagonite tuff.
It is abundant in Iceland (the type locality Palagonia is actually in Sicily, but Iceland's móberg ridges are classic), Hawaii, and other basaltic volcanic regions.
How to identify it
Recognize palagonite by its earthy yellow-brown to orange or reddish color rimming or replacing dark basaltic glass shards, often in a tuff or pillow-lava setting. It is dull to waxy, relatively soft, and may feel clay-like.
It commonly appears as rinds around fresh black glass cores and as the cement binding glassy ash.
Distinguish it from limonite or ordinary iron staining by its association with basaltic glass and tuff, and from unaltered sideromelane (which is fresh, dark, and glassy) by its hydrated, oxidized, lighter color.
Uses & significance
Palagonite tuff is used locally as a building and dimension stone (notably in Iceland) and as a lightweight aggregate.
Scientifically it is highly valued as a Mars analog material for testing how basalt weathers under water-limited conditions, and as a record of past volcano-water and even volcano-ice interactions.
It has no gem use and little metaphysical following; its importance is geological and planetary rather than ornamental.
Frequently asked questions
Is palagonite a mineral?
No. It is an alteration material — a mixture of clays, zeolites, and iron oxides formed when basaltic glass reacts with water — not a single mineral species.
Why is palagonite important for Mars research?
Palagonitic soils chemically and spectrally resemble altered basaltic material on Mars, so they serve as Earth analogs for studying the Martian surface.
What color is palagonite?
It is typically yellow-brown, orange-brown, or reddish, contrasting with the dark glass it replaces.
Where is palagonite found?
It is common in basaltic volcanic areas with water interaction, such as Iceland's móberg ridges, Hawaii, and many submarine and subglacial eruption deposits.
Palagonite guides
In-depth guides for identifying, valuing, and understanding Palagonite.
