At these coordinates you are looking at a weathered volcanic outcrop where something “looks like” one mineral, but is actually made of another. These features are called pseudomorphs.
A pseudomorph forms when a mineral (or crystal aggregate) is replaced by a different mineral, but the external shape of the original is preserved. In other words:
In the rock here, the pseudomorphs appear as distinct, often blocky or crystal-like shapes that stand out from the surrounding matrix by color, texture, or resistance to weathering.
picture: kikekatze
Why are they up in the wall, not at knee height?
A key observation at this site is that pseudomorphs occur several times and not only close to the ground—some are up to several meters above today’s surface level. That is not a coincidence and it is not “because the minerals grew only up there”. It is mainly about pathways and zones where fluids once moved through the rock, and about what part of the outcrop is exposed today.
Pseudomorphs tend to form where there was:
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a permeable pathway for water/hydrothermal fluids (fractures, joints, flow boundaries)
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enough time for chemical reactions to proceed
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repeated wetting / heating events or long-term groundwater circulation
Those pathways can be vertical, diagonal, or layered, and they are often expressed in an outcrop as bands, zones, or patches. When erosion later cuts into the hillside, we do not “create” the pseudomorphs—erosion simply reveals them at the height where that altered zone is intersected by today’s cliff face.
So the height tells a story: the outcrop is like a sliced cake. The pseudomorphs are not “floating” in mid-air; you are seeing a cross-section through an alteration zone that happens to be exposed between roughly ground level and several meters above it.
How pseudomorphs form
1) The starting point: volcanic rock with primary minerals
This is volcanic rock (commonly basaltic in Iceland). When basalt cools, it contains primary minerals and glassy/very fine material. Typical primary components can include:
Not all minerals are equally stable at Earth’s surface. Some react quickly with water and dissolved CO₂, others are more resistant.
2) Fluids enter: water finds weaknesses
Water and/or hydrothermal fluids enter the rock through weaknesses such as:
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joints and fractures
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flow boundaries between lava layers
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zones of broken or vesicular rock
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tiny pore spaces and microcracks
Once water can circulate, it can transport dissolved ions and trigger chemical reactions.
3) The replacement: dissolution + precipitation
Pseudomorphs typically form by replacement:
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The original mineral begins to dissolve (it breaks down chemically).
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At the same time (often in the same tiny space), new minerals precipitate from the fluid.
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If the replacement happens gradually and “front-like”, the outer shape of the original crystal can remain visible, even though the inside is now different material.
This is why pseudomorphs are so useful: they preserve a memory of the original mineral habit, even when the original mineral is gone.
4) Why some stand out so clearly
After replacement, the new mineral assemblage may be:
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harder than the surrounding rock → it sticks out (positive relief)
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softer than the surrounding rock → it weathers out (small recess)
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different in color (oxidation, clay alteration, carbonates, silica)
Over time, freeze–thaw, rain, wind, and chemical weathering increase the contrast, making pseudomorphs easier to spot.
What the “height pattern” can tell you
If you see pseudomorphs repeatedly at similar levels or clustered in a wall section, this often indicates:
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an alteration zone controlled by a fracture network, or
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a specific lava flow boundary that acted as a fluid pathway, or
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an old groundwater level or long-lived seepage zone, or
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a combination of these
It is very common that such zones are not uniform: fluids move where the rock allows it. That is why you may see pseudomorphs in pockets and lines rather than everywhere.
Observations you can make on site
When you visit, try to connect the theory to what you see:
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Look at shape: are the forms crystal-like, blocky, rounded, or irregular?
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Look at texture: smoother than the host rock or more crumbly?
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Look at distribution: isolated spots or aligned along cracks/bands?
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Look at height: do they cluster in a certain vertical range?
These are the exact clues that help distinguish pseudomorphs from random erosion features.
Logging Tasks
1. Please answer the following questions and send your answers (in English or German) via Message Center or email.
You may log immediately; if something is unclear, I will contact you.
a. Identify and describe one pseudomorph
Choose one clearly visible pseudomorph (you can pick one high up or one closer to eye level).
Describe:
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its approximate shape (blocky, crystal-like, lens-shaped, irregular…)
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its approximate size (height/width)
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how it differs from the host rock (color, texture, “sticks out” or “sits in”)
Based on your description: why is it plausible that this is a replacement feature and not just a random fracture block?
Send me a picture with your answers, dont post it with your log.
b. The height question – where are they, and what does that imply?
Estimate the height above the ground of at least two pseudomorphs you can see (for example: ~1 m and ~3–4 m).
Do they appear:
Explain what the observed height distribution suggests about fluid pathways (fractures, joints, or flow boundaries).
c. Evidence for pathways – connect pseudomorphs to rock structure
Look closely at the wall near your chosen pseudomorph(s).
Describe at least two structural clues that could have guided water/fluids, for example:
Explain briefly how such structures would help pseudomorphs form.
d. Your own explanation: from “original mineral” to pseudomorph, and why this level is exposed today
In your own words, summarise:
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how a mineral can be replaced while keeping its shape (dissolution + precipitation), and
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why you can see multiple pseudomorphs at several meters height today (alteration zone + later erosion exposure).
2. Picture
Take a picture of you either at the coordinates or somewhere else in the close area. If you do not want to show your face, write your name and date on a piece of paper and take a picture of that in front of the outcrop.
picture: kikekatze
Safety
Do not climb the wall. Please leave the site as you found it.
Sources:
Pseudomprhs
Geology of Iceland
Geology
Alex Strekeisen