Gneiss (pronounced "nice") is a metamorphic rock consisting mostly of quartz and feldspar and showing distinct layering or banding. The layering of a gneiss may be weak or well-developed and consists of varying concentrations of biotite, garnet, hornblende, mica, and other minerals . These structures do not record a layered deposition process but arise from preferential recrystallization along flow or stress lines during metamorphosis of the parent rock.
The gneiss is the light coloured rock. It contains very coarse crystals of pale feldspar, some coarse glassy quartz crystals and some fine dark mineral in a rough linear arrangement typical of many metamorphic rocks. It was formed about 1800 million years ago during the kimban orogeny (Mountain building phase), Movements deep in the earth's crust generated heat and pressure which altered previously formed rocks to create the gneiss.
The black rock, dolerite forms dykes in the gneiss. It contains mostly a dark mineral called Hornblende and a small amount of light coloured feldspar. It was formed when magma, molten rock from deeper in the earth's crust, where it was cooled and crystallised to form hard dykes.
The rocks have been exposed to view by natural processes of weathering and erosion.
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Q1 Describe the different colour rocks you see here and how do the different colour rocks differ from one another.
Q2 Can you see any Quartz and how much can you see here.