Please note, to adequately complete this earth cache you will need to enter Aboriginal land and pay for a permit to do so, you will also need to visit at low tide. Tides Click here Thiithaarr-warra Elder, Eddie Deemal runs the camp and a day pass for the beach can be purchased from him at the camp grounds for $10. Click here 4wd is also recommended but not essential.
By definition Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt. Sand can also refer to a textural class of soil or soil type; i.e. a soil containing more than 85% sand-sized particles by mass.
In terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm (or 1⁄16 mm) to 2 mm. An individual particle in this range size is termed a sand grain. Sand grains are between gravel (with particles ranging from 2 mm up to 64 mm) and silt (particles smaller than 0.0625 mm down to 0.004 mm). Sand feels gritty when rubbed between the fingers, silt, by comparison, feels like flour.
The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica, usually in the form of quartz.
Quartz is a chemical compound consisting of one part silicon and two parts oxygen. It is silicon dioxide (SiO2).
Quartz is the most abundant and widely distributed mineral found at Earth's surface. It is present and plentiful in all parts of the world. It forms at all temperatures. It is abundant in igneous, metamorphic, and sedimentary rocks. It is highly resistant to both mechanical and chemical weathering. This durability makes it the dominant mineral of mountaintops and the primary constituent of beach, river, and desert sand.
Quartz is an extremely hard mineral and does not weather easily. Some sedimentary rocks in particular, such as sandstone, have a large amount of quartz sand already incorporated into them. They act as a ready source of sand, easily eroded quartz grains that have already been separated from their original mineral matrix. Grains from these rocks may be rough or already smooth, depending on the conditions in which they were originally formed.
A rock is weathered mechanically by rain, heat fluxes, expansion of ice and roots, and impacts of rock upon a surface after a piece has been detached from the bedrock. The sharp pieces which break off join the sand in the stream system. The non-quartz components are more likely to fracture, creating zones of weakness which are preferrentially eroded as the clast moves downstream, occassionally knocking a quartz grain loose.
Rains bearing acid, groundwater, soil processes, and biotic (organism-caused) effects all act to affect rock and is called Chemical weathering. Some non-quartz minerals break down into clay minerals while quartz, and other chemically-resistant materials are isolated and washed downstream to the ocean.
Chemical and physical weathering may both erode a rock at the same time.
Depending upon how far the sand travels before it gets to the ocean it may be either angular or very rounded and smooth. The more distance a grain travels the more likely it is to be knocked into other clasts, breaking off sharp edges, leaving a smoother, more rounded surface,
The stunning colours here at Elim beach are what make it so special. Most Australians understand that our beautiful red colours come from ‘rust’, but what about the other colours seen here?
We were unable to find much more specific information about the coloured sands at this particular beach, we did contact a local geologist. “The sand units are simply called the Flannery Sands. The red to orange colouration is entirely due to the proportion of iron oxide (fine haematite, limonite, goethite) present. The grey colouration bands in some would be a combination of ilmenite, rutile, zircon, and magnetite which are reported in minor concentrations from there.”
We were able to determine the following minerals are the cause for the following colours at Elim beach,
Iron – Red
Aluminium – Purpleish
Vegetable Matter – Black/Brown
Biotite – Black/Silver
Rutile – Pinkish
Zircon – Yellow/Gold
Monazite – Brown/Red
To log this Earth Cache we require you to consider the information presented to you in this Earth Cache, walk or drive the track and look at the area, perhaps you will need to do some research of your own, then message us with the following answers to the best of your ability;
1. From your chosen vantage point, how many colours can you see, what are they? What colour is most prevalent?
2. As you move along the beach feel the different colours, is there a difference?
3. Looking at the area and remembering to consider the information given in this earth science lesson, what conclusions do you draw about the source of this sand and its age?
4. A photo of your team or GPS with the sands in the background, upload as many photos as you like we would love to see the area again and again. (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 John Nethery, Geology.com, Wikipedia.
