Have you ever found a rock in the shape of a love heart? Or shaped like Australia? What about one that looks like a flower or a shell? Or seen a shape in a flat rock surface that looks just like a human footprint? The forces of wind, water, and time constantly work to shape rocks into a range of shapes, sizes and colours — including ones that look like past life. Scientists call these features pseudofossils. Pseudofossils are formed by inorganic (non-living) processes but look like fossils or other signs of life.
Minerals and elements can also grow into very organic-like shapes given the right conditions. The shapes of these growths are related directly to the minerals themselves and their preferred form, or crystal habit. For example, the preferred crystal habit of pyrite, known as ‘fool’s gold’, is perfect cubes that look as if they were made by human hands.
The most common types of mineral growths are formed by manganese minerals. These tend to be black or another dark colour (see pictures A to C, below), although gypsum (F) and other salt minerals can also form growths mistaken for fossils. Liesegang banding (D) is also formed by the precipitation of minerals in coloured rings within rocks. Mineral growths filling cracks and fractures (E) can often resemble trace fossils, including tracks and trails.
Colour changes and banding in these features can be due to subtle changes in the mineral chemistry during time or changes in oxygen levels or oxidation state. A good example of this can be seen in iron-oxide minerals. Hematite is red-brown and often formed in oxygen-rich environments, while magnetite is black-brown and forms in oxygen-poor conditions, and goethite is yellow-brown and tends to form in wetter conditions.
In the retaining wall at GZ you will find some examples of pseudofossils.
To claim this Earthcache please send your answers to the following questions in a message within 7 days of your log otherwise it may be deleted.
1. Which of the pseudofossils pictured above (A-F) are found at GZ? Bonus points if you can name it.
2. Describe the pseudofossils you find - what do they look like? Colour, shape, size, etc.
3. Why do you think they are often mistaken for fossils?
4. One rock is a distinctly different colour to the others. State what colour it is and suggest what conditions caused it.
References:
https://en.wikipedia.org/wiki/Pseudofossil
https://www.dmp.wa.gov.au/Pseudofossils-1663.aspx
https://collections.museumsvictoria.com.au/articles/11002
Please do not post photos that give away the answers, however adding a photo near GZ is encouraged.