Geo mum just loves rocks, so when we ended up in the area recently she was beside herself when she discovered Moon Rocks!
Known locally as "Moon Rock" they are very common and after spending a little time in the area you will have to agree conspicuous! They range in size from golf ball to boulders weighing several tonnes. Local residents and councils seem to be very proud of these unique local formations and use them as decorations in nearly every surrounding township.
The nodules are concretions formed in sediment by the accumulation of limestone (calcium carbonate) within mud on the floor of the ancient sea which covered this part of Queensland about 100 million years ago. They are the result of chemical processes, not of water erosion. The nodules are not themselves fossils but they may contain fossils, especially seashells forming the nucleus around which carbonate accumulated to form the nodule. Sometimes wood and bone are found at the centre of concretions.
A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin con meaning 'together' and crescere meaning 'to grow'. Concretions form within layers of sedimentary strata that have already been deposited. They usually form early in the burial history of the sediment, before the rest of the sediment is hardened into rock. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum.
There is an important distinction to draw between concretions and nodules. Concretions are formed from mineral precipitation around some kind of nucleus while a nodule is a replacement body.
Descriptions dating from the 18th century attest to the fact that concretions have long been regarded as geological curiosities. Because of the variety of unusual shapes, sizes and compositions, concretions have been interpreted to be dinosaur eggs, animal and plant fossils (called pseudofossils), extraterrestrial debris or human artifacts.
Detailed studies published in peer-reviewed journals have demonstrated that concretions form subsequent to burial during diagenesis. They quite often form by the precipitation of a considerable amount of cementing material around a nucleus, often organic, such as a leaf, tooth, piece of shell or fossil. For this reason, fossil collectors commonly break open concretions in their search for fossil animal and plant specimens. Some of the most unusual concretion nuclei, are World War II military shells, bombs, and shrapnel, which are found inside siderite concretions found in an English coastal salt marsh.
Depending on the environmental conditions present at the time of their formation, concretions can be created by either concentric or pervasive growth. In concentric growth, the concretion grows as successive layers of mineral accrete to its surface. This process results in the radius of the concretion growing with time. In case of pervasive growth, cementation of the host sediments, by infilling of its pore space by precipitated minerals, occurs simultaneously throughout the volume of the area, which in time becomes a concretion.
Moon Rocks are commonly composed of a carbonate mineral such as calcite; an amorphous or microcrystalline form of silica such as chert, flint, or jasper; or an iron oxide or hydroxide such as goethite and hematite. They can also be composed of other minerals that include dolomite, ankerite, siderite, pyrite, marcasite, barite and gypsum.
Although concretions often consist of a single dominant mineral, other minerals can be present depending on the environmental conditions which created them. For example, carbonate concretions, which form in response to the reduction of sulfates by bacteria, often contain minor percentages of pyrite. Other concretions, which formed as a result of microbial sulfate reduction, consist of a mixture of calcite, barite, and pyrite.
Concretions are found in a variety of rocks, but are particularly common in shales, siltstones, and sandstones. They often outwardly resemble fossils or rocks that look as if they do not belong to the stratum in which they were found. Occasionally, concretions contain a fossil, either as its nucleus or as a component that was incorporated during its growth but concretions are not fossils themselves. They appear in nodular patches, concentrated along bedding planes, protruding from weathered cliffsides, randomly distributed over mudhills or perched on soft pedestals.
We have brought you a little out of town where you can see them ‘in the wild’. There is also a nice display of them at Commemorative Cairn Plaque on the Flinders Hwy in Richmond, some say this is actually a monument recognising the pumpkin scones made famous by Lady Flo Bjelke-Petersen, or down at the Bush Tucker Garden at Fred Tritton Lake (both waypoints listed on this cache).
If you are lucky enough to be visiting the area during the Fossil Festival make sure you check out the World Champion Moon Rock Throwing Competition. If you think you can throw a 20kg moon rock more than 5 meters you might even have a chance at a win!
To log this Earth Cache we require you to wander around and look at the area and what is available to you visually, consider the information given and perhaps if you need to do some research of your own, then message us with the following answers to the best of your ability;
1. Find some Moon Rock, examine it, what does it feel like?
2. The Moon Rocks here are approximately what size?
3. In this area there are many broken moon rocks, can you identify any fossils in them? (we easily found two different types without breaking any rocks open here)
4. A photo of your team, GPS with a Moon Rock with your log and answers. (Optional)
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers within 24 hours. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted.
Source: Wikipedia, travelling-australia.info,
