The geology of coal
Coal is a combustible sedimentary rock of organic origin composed mainly of carbon, hydrogen and oxygen, with lesser amounts of nitrogen, sulphur and other elements. There is always some water present, and some inorganic matter that forms an incombustible residue known as ash. Coal forms from the decomposition, heating and compression of plant matter.
Coal formed millions of years ago when large areas of the earth were covered with swamps, where plants - giant ferns, reeds and mosses - grew. As the plants grew, some died and fell into the swamp waters. Subsequent generations of plants grew and died, and in time, there were thick layers of dead plants rotting in the swamp. The surface of the earth changed and water and dirt washed in, sealing off the rotting material, and stopping the processes of decay. More plants grew, but they too died and fell, forming separate layers. After millions of years many layers had formed, one on top of the other. The weight of the top layers and the water and dirt packed down the lower layers of plant matter. Heat and pressure produced chemical and physical changes in the plant layers which forced out oxygen and left rich carbon deposits. In time, material that had been plants became coal. Coal is thus known as a fossil fuel - it is literally compressed plant fossils.
Coal is classified by rank, which is a measure of the amount of alteration it has undergone during formation. Consecutive stages in evolution of rank, from an initial peat stage, are brown coal (or lignite), sub-bituminous coal, bituminous coal, and anthracite. Increase in rank is due to a gradual increase in temperature and pressure that results in a decrease in water content and therefore an increase in carbon content. A continuous gradation occurs between these ranks. Sub-bituminous coal, bituminous coal and anthracite are together known as black coal.
Coal is discovered in Australia
Escaped convicts William & Mary Bryant are considered to have made the first discovery of coal in Australia, when they discovered coal near the entrance to Glenrock Lagoon on 30 March 1791. They had recently escaped from Sydney, and were on their way to Timor in a stolen boat when they landed, presumably at Burwood Beach. They named it Fortunate Creek because they found food there and friendly Aborigines. However, the news did not get back to Sydney and it was Lieutenant John Shortland RN who received credit for the discovery of coal in Newcastle in 1797. Even today, coal can still be found in the cliff face on the northern headland at the mouth of Glenrock Lagoon, and this area is your target for this EarthCache.
Professor Edgeworth David later stated that the exposures of the Newcastle coal seams in the cliffs in this area were among the finest of their kind in the world. The same coal seams examined by the early scientists are easily seen today in the coastal headland in the Merewether and Glenrock areas.
How to get there
2021- please see our maintenance logs for up to date access info after track closures put in place.
In completion of this earthcache, you will need to walk to the EarthCache site. You can park for free at the parking coordinates (Burwood Road), and walk along the Yuelarbah Track, it is a well formed, 2.5km (5km return) track that follows Flaggy Creek all the way to Burwood Beach and the place of interest. Stop half way at Leichhardt's Lookout for a rest and to admire the view over Glenrock Lagoon. There are some relics from past mining operations to see on the way. The track does involve one section of numerous (>30) steps, and some gentle inclines. You do not need to, and should not, deviate off the track.
To log this earthcache:
Please email or message via the website, the answers to the following questions:
1. On the way to the EarthCache, you will pass a relic of past coal mining days, shown as a reference point (RELIC). What is it?
2. When standing at the EarthCache coordinates, how many coal seams are prominent? Describe the appearance of the seams?
3. Observe closely the appearance of the coal within the seams - would you classify it as brown or black coal? Can you identify layers within the coal structure?
4. Include a photo of yourself or GPS at GZ in your log.
You are free to log your find before you hear back from us, we will reply to all submissions, and will let you know if there are any problems. Logs will be deleted if your answers aren't received after a reasonable time.
Please note: as of June 2019 photos can be required as part of the logging tasks for an EarthCache.
This EarthCache is situated in a State Conservation Area, so ensure that NSW National Parks and Wildlife Service regulations are followed during your visit. Further information, including park safety messages, can be found at the following link:
http://www.nationalparks.nsw.gov.au/visit-a-park/parks/Glenrock-State-Conservation-Area
References:
1. Australian Government Geosciences Australia - Atlas of Minerals resources, Mines and Processing Centres
http://www.australianminesatlas.gov.au/education/fact_sheets/coal.html
2. Geological Sites of NSW - Cartoscope Pty Ltd
http://www.geomaps.com.au/scripts/huntervalleycoal.php
3. Kentucky Coal and Energy Education Project
http://www.coaleducation.org/q&a/how_coal_formed.htm