This Earthcache will bring you to a feature on Cape Woolamai known as "The Pinnacles". This rock formation evolved millions of year ago and is one of the most spectacular spots on Phillip Island. This geological feature is well worth the long walk out. It is one of the oldest rock formations on Phillip Island.
About 360 million years ago, moltern rock forced it's way up from the earths core. It cooled very slowly beneath the ground, forming the pink granite which is Cape Woolamai's foundation. The granite extends down to an unknown depth below sea level. The Pinnacles you see are the result of cracks which formed as the rock was cooling and shrinking, with help of the wind, rain and waves has sculptured this feature to its present day beauty.
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. These 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.
Granite is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 • 1019 Pa·s.Melting temperature is or 1215–1260 °C (2219–2300 °F)
Granite has poor primary permeability but strong secondary permeability.
Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids.
The term "granitic" means granite-like and is applied to granite and rocks of similar composition or texture.
Chemical composition
A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses:
SiO272.04% (silica), Al2O314.42% (alumina), K2O4.12%, Na2O3.69%, CaO1.82%, FeO1.68%, Fe2O31.22%, MgO0.71%, TiO20.30%, P2O50.12%
MnO0.05%
LOGGING REQUIREMENTS
No1: How many Pinnacles of similar height can you see from GZ?
No2: Can you describe what you see at the base of the cliff directly below GZ .
No3: What are the pinnacles made of?
Please email me your answers, Thank you.
ACCESS TO 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