WELCOME TO THE CAPE WOOLAMAI GRANITE QUARRY
In the Devonian times the molten rock forced its way up from the earth’s interior to form a large blister deep beneath the mountains. Its temperature was originally more than 600 degrees Celsius and it cooled very very slowly beneath the ground, gradually crystallizing into pink granite. As the cooling rock shrank, cracks (known as joints) formed between the blocks of rock. When the mountains were worn down the granite core was laid bare, it was carved by rivers and the waves of the sea into the majestic promontory we now see as Cape Woolamai. The joints can be seen as fractures in the cliff face, particularly at The Pinnacles, where tall narrow blocks lean to the sea.
A close look at a piece of Woolamai granite through a magnifying glass shows that it contains glassy quartz crystals, pink opaque feldspar and shiny flakes of mica. There are also thin veins of sugary quart-zose rock, known as aplite, squeezed into the granite at a late stage as it cooled.
The quarry was established in 1891 for mining of the unique Cape Woolamai granite. To remove the granite they used the feather and wedge method. The steel wedges were driven into the rows of drilled holes. A jetty was constructed from the granite blocks enable loading into vessels for shipment of the granite to Melbourne. The quarry was unfortunately short lived. The last load of granite was taken in 1898. On 10th December 1892 the ketch Kermandie disappeared at sea heavily laden with the Cape Woolamia granite. A couple of buildings in Melbourne had granite from the quarry as well as the Melbourne and Hawthorn cemeteries.
WHAT IS THE FEATHER AND WEDGE METHOD
Plug and feather, also known as plugs and wedges, feather and wedges, wedges and shims, pins and feathers and feather and tare refers to a technique and a three-piece tool set used to split stone. Variations of the plug and feather method have been used since ancient Egyptian times. With this simple mechanical technique, the stone was first measured and marked. Bronze plugs and feathers were then driven into grooves which had been previously cut with a chisel and mallet.
WHAT IS GRANITE
Granite is a common type of felsic intrusive igneous rock which is granular and phaneritic in texture. The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. The term 'granite' also applies to a group of intrusive igneous rocks with similar textures and slight variations on composition and origin. These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals. Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is known as a granite porphyry. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. By definition, granite is an igneous rock with at least 20% quartz and up to 65% alkali feldspar by volume. Granite differs from granodiorite in that at least 35% of the feldspar in granite is alkali feldspar as opposed to plagioclase; it is the potassium feldspar that gives many granites a distinctive pink color. The extrusive igneous rock equivalent of granite is rhyolite.
THE MAKE UP OF CAPE WOOLAMAI GRANITE.
Quartz crystall
Quartz is the second most abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2.
There are many different varieties of quartz, several of which are semi-precious gemstones. Especially in Europe and the Middle East, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hard-stone carvings
Feldspar
Feldspar are a group of rock-forming tectosilicate minerals that make up as much as 60% of the Earth's crust.
Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock.Rock formed almost entirely of calcic plagioclase feldspar (see below) is known as anorthosite. Feldspars are also found in many types of sedimentary rocks
Mica
The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having nearly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.
The word mica is derived from the Latin word, mica, meaning a crumb, and probably influenced by micare, to glitter.
Aplite
Aplite the name given to intrusive rock in which quartz and feldspar are the dominant minerals. Aplites are usually very fine-grained, white, grey or pinkish, and their constituents are visible only with the help of a magnifying lens. Dykes and threads of aplite are commonly observed traversing granitic bodies; they occur also, though less frequently, in syenites, diorites, quartz-diabases and gabbros.
Aplites usually have a genetic affinity to the rocks they intersect. The aplites of granite areas, for example, are the last part of the magma to crystallize, and correspond in composition to the quartzo-feldspathic aggregates that fill up the interspaces between the early minerals in the main body of the rock. They bear a considerable resemblance to the eutectic mixtures which are formed on the cooling of solutions of mineral salts, and remain liquid till the excess of either of the components has separated out, finally solidifying en masse when the proper proportions of the constituents and a suitable temperature are reached.
The essential components of aplites are quartz and alkali feldspar (the latter usually orthoclase or microperthite), microcline and albite. Crystallization has been apparently rapid (as the rocks are so fine-grained), and the ingredients have solidified almost at the same time. Hence their crystals are rather imperfect and fit closely to one another in a sort of fine mosaic of nearly equi-dimensional grains. Porphyritic feldspars occur occasionally and quartz more seldom; but the relation of the aplites to quartz-porphyries, granophyres and felsites is very close, as all these rocks have nearly the same chemical composition.
LOGGING REQUIREMENTS
No1 What are you standing on at GZ
NO2 Approximately 100 mtrs from GZ when facing North east describe what you see.
NO3 Near GZ (approx 20 mtrs) when facing the water there are some rocks please tell me about these rocks.
NO4 At GZ there is a seam of something what do you think it is?
Please email me your answers
ACCESS TO THE EARTHCACHE
To access this earthcahe you will need to park at the Woolamai Surf Beach carpark. Please if it is warm take plenty of water with you. The tracks out to GZ are pretty well marked but do keep an eye out for snakes. You need to allow a few hours to complete the walks out here but it is well worth it . A huge thanks to Hearse068 and BorisB&Natasha for taking the time to come with me and experience this great area. Don't for get to take a camera with you as you will find lots of spots for photos