This is a simple Earthcache to learn about two features (phenocrysts and veins) of this large natural granite outcrop. First up, some history.
Dog Rock is a large, natural granite outcrop that is located along Middleton Road between Middleton Beach and the centre of Albany.
The rock is a prominent landmark and has the shape of a dog's head when viewed from the western side, leading to the name. Dog rock has become a popular tourist attraction for the area. The Noongarpeople know the rock as Yacka which means "wild dog tamed"; it is thought to be an ancient territorial boundary marker. Local Aboriginal people will not camp near the rock or shelter beneath it, although the reason is not known.
In 1921 the Council proposed demolishing the rock with explosives so as to widen the road. The idea was met with protests and petitions along with an angry exchange during a council meeting resulting in the proposal being quashed.
The Royal Automobile Club labelled the rock a danger to traffic in 1938 as it encroached onto the road. The local authorities then painted the distinctive white collar around the base of the rock to make it more visible.
In the 1960s, the manager of the local radio station 6VA. suggested that the rock should be moved to the roundabout of Albany Highway, Denmark Road, North Road and Chester Pass Road. He believed that this would make it a more central tourist destination, and that the rock could be cut into slices and moved piece by piece and then rebuilt at the new site.
The rock was classified by the National Trustin 1973 and adopted into the municipal inventory in 2001.
Ok, now onto today's Earth Science lesson.
Formation
Around 1350 million years ago, Antarctica and Australia collided and were joined together for almost 1300 million years! Mount Clarence and Mount Melville are two large granite outcrops formed during this continental collision. These rocks were formed many kilometres in the Earth's crust by the slow cooling of molten rock or magma during this continental collision. This collision would have created an extensive mountain range along the south coast. Weathering and erosion has long removed these lofty peaks but the mountain roots remain and form the geological foundations of most of the south coast.
Minerals
Granites are typically made up of feldspars, quartz, and mica.
Feldspar minerals are abundant in granite. They are usually white, gray, pink or reddish in color. Many grains will exhibit two directions of cleavage that intersect at right angles. Orthoclase commonly forms as large tabular crystals while the plagioclases form as interlocking grains.
Quartz will usually be a transparent mineral that is colorless or gray in color. Many grains will exhibit a conchoidal fracture and a glassy lustre.
Mica minerals expected in granites include muscovite and biotic.Micas occur in very thin sheets. They will often be in "books" of numerous sheets stacked upon one another. The surfaces of these sheets will have a highly reflective or look like a book of cards.
Hornblende is typically the minor dark coloured mineral that may be present.
Grain size and phenocrysts
These rock types are typically medium grained (1-5mm), coarse grained (5mm to 3cm) and very coarse grained (>3cm). Phenocrysts are the large crystals that are present in the rock. In pegmatites these phenocrysts can be lunch box sized but here at Dog Rock, they are smaller.
Earthcache questions
There are some larger grains or crystals of orthoclase feldspar in the Dog Rock granite. From the path and under the mouth of the dog, they may be easier to see.
Q1. Describe the colour, size and shape of these phenocrysts, the largest grains in the rock.
Stand back and look at the southwestern side of Dog Rock. There are two prominent lines on the rock. These are veins of feldspar and quartz.
Q2. How thick are these veins in centimetres and what angle are they dipping from the horizontal? (Zero degrees for flat and 90 degrees for vertical).
Please log the cache and add a photo of Dog Rock (optional) straight away. You can ubmit the answers to the two questions within a few days but logs without answers will be discreetly deleted within 14 days.