Trousers Point is one of the island's iconic granite locations with the rich colours and textures of these rock outcrops dominating the landscape here.
With the high ranges of Strzelecki National Park rising above it, Trousers Point feels like a natural base camp on the island from where you can explore the rich geological heritage that surrounds you.
At Trousers Point you also have the chance to look more closely at these intriguing rocks. They reveal the dramas which unfolded here from around 380 million years ago deep within the earth, with mountain building episodes, melting rocks and later erosion. Enjoy the simple pleasure of exploring the granite textures and details now finally exposed to the sunlight.
Phenocrysts are large crystals that are amongst the first things to form as the magma slowly cools deep within the earth.
They stand out from the surrounding finer grained rock. Geologists use their presence or absence as a key diagnostic tool to classify igneous rocks.
Looking at the granites at Trousers Point you can see quite big feldspar crystals.
Feldspar is a common mineral that makes over up 40% of the earth’s crust. It is used in making glass and ceramics.
There are around ten different types of granite found on Flinders Island.
One of the quickest ways to spot the differences between them is by colour.
Colour is a simple code to the mineral composition of the rock.
Colourless to dark grey = quartz.
Pink to white = feldspar.
Black or silver = mica.
Mica is the first mineral to crystallise in the magma.
As well as standing apart as black crystals in the rock you may spot mica grains even within the feldspar crystals.
Looking at the granites at Trousers Point you can see quite big crystals. You can also pick out the feldspars, the quartz and various other minerals in the rock.
At a larger scale there is also erosion occurring where the rock breaks down into the crystals that eventually make the sand on the beach. This means that at locations like Trousers Point it's not just about rocks, but also about processes – the geological process making the beaches.
Scientists have identified between seven to twelve different types of granite on Flinders Island with these ranging most obviously in colour and crystal size and texture.
The pinker rocks occur as a result of a lot of quaartz. Others are greyer with a lot of feldspar in them while some have a lot of black minerals like miotites.
The big crystals are called phenocrysts and you often hear talk about phenocryst bearing granite. Looking closely at the rocks around Trousers Point you can see some of the variability in the granite. Some are more equi-granular without the big crystals. This sort of variability is seen all throughout the granites on the island.
Down on the beach you walk over the granites - an igneous rock that has some quartz in it, some feldsar and typically a mica phase.
Here we can see quite clearly the pink colours - that’s the quartz, the white crystals are the feldspars and mica is there in the black flaky minerals.
So that’s main constituents of the granite. These feldspars are quite exceptional really. Within the feldspar you get little inclusions of mica as well which is quite interesting. As the feldspar grew it would have captured the mica that was already crystallised in the melt.
In places you can see large elipsoids with white halos around them. These are called inclusions within the granite.
These inclusions are older than the granite that surrounds them. When the newer granite was intruding in through the crust it’s broken up blocks of the pre-existing granite and included them in the new rock mix. Some of these inclusions can be up to 2-3 metres big here along the coast.
