Darwin City and its suburbs are bounded along the western shore by sea cliffs, between 1-30 m in height, and shore platforms at the base of headlands along with small pocket beaches and some longer beaches up to 10 km in length.
The low lying coastal cliffs at East Point consist sedimentary rock commonly known as Porcelainite which as been naturally eroded, largely by wave action from the ocean to form horizontal to gently undulating bedded strata of varying colours with large and small caves which are common at East Point and Casuarina to the north.
Cliff erosion is a natural process which occurs in stages. Firstly, fresh water surface runoff, groundwater flows and seawater gradually erode the lower to mid cliff areas containing soft dolomitic/carbonate and siltstones forming fissures and cracks within the rock. Over a period of time the cracks become enlarged and break up large sections of rock from the parent material. At high tide the waves break on the lower cliff face which break the joints in the rock even further until eventually large sections of rock collapse onto the beach. The caves formed by this process then tend to concentrate the wave energy resulting in even greater cliff collapses and more erosion with larger embayments along the coast. Cliff erosion along the Darwin harbour coastline can also be increased by surface, stormwater and groundwater flows at particular points over the cliffs which also dissolve the fragile carbonate/silicate rocks leading to cliff instability. This process is enhanced by the acidic nature of the ground water in the Darwin region. Nutrient rich stormwater and effluent discharging from sewerage outfalls near East Point are also the likely cause of algal staining and pitting of the dolomitic layers of the cliffs and are contributing to the bio-erosion occurring in these areas.
The low lying coastal cliffs at Nightcliff consist sedimentary rock commonly known as Porcelainite which as been naturally eroded, largely by wave action from the ocean to form horizontal to gently undulating bedded strata of varying colours with large and small caves along the coast
Porcelanite is a hard, dense rock that takes its name from its resemblance to unglazed porcelain. Frequently porcelanite is an impure variety of chert containing clay and calcareous matter; when of this nature it is composed chiefly of silica.
Porcelanite
The porcelanite of some authorities is a silicified tuff, a rock composed of volcanic fragments that has been altered to silica, or even metamorphosed marl, calcareous rock fragments altered by heat and pressure. One porcelanite, common in lignite deposits, is formed from the fusion of shales and clay on the floor, walls, and roof of burned coal seams.
There is also a local group that come here every Saturday night to enjoy another hobby. 'Rocksitting' evolved from the great Darwin tradition of sitting down and having a few beers with ya mates. Back in 1974 a group of journalists gathered at East Point Reserve on a Saturday afternoon to sink a few tinnies (cans of beer), spin a few yarns (tell a story) and watch the brilliant Sun set over the Arafura Sea. Needless to say this became a regular event and the Rocksiters club began. I'm sure they don't talk about these rocks too much 
Q1 Describe the rocks in your own words including size, colours you see and texture.
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