This geological walk commences at Parliament House on the North West corner of the intersection. Next cross King William Street to 2 King William Street and the Adelaide Club. Finally proceed north to the to the North East corner to visit the Boer War Memorial.
On the tour you will see granite, sandstone, marble, limestone, and a slate pavement. South Australia's central position within the Australian continent gives the state the advantage of hosting rocks with a wide range of ages and lithologies, many of which are proven materials for dimension stone.
Granite is a plutonic igneous rock formed by slowly cooling pockets of magma trapped beneath the earth's surface. Granites are typically a hard rock with visible crystalline texture, rich in quartz and feldspar. Granite is the most common igneous rock of the Earth’s crust. Crystals are produced whenever a solid is formed gradually. Granites are crystalline rocks. If the granite source material, magma, is cooled rapidly, numerous seed crystals form and grow only into tiny crystals; but if the material is cooled slowly, a few seed crystals will grow into large crystals.
Marble is a rock resulting from metamorphism of sedimentary carbonate rocks, most commonly limestone or dolomite. Metamorphism causes variable recrystallization of the original carbonate mineral grains. The resulting marble rock is typically composed of an interlocking mosaic of carbonate crystals. Pure white marble is the result of metamorphism of a very pure limestone or dolomite. The characteristic swirls and veins of many colored marble varieties are due to various mineral impurities, which were originally present as grains or layers in the limestone.
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. Many limestones are composed from skeletal fragments of marine organisms such as coral or mollusks. Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls, and around hot or cold springs.
Sandstone is a clastic sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow, red, gray, pink, white and black.
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock. Slate is mainly composed of quartz and muscovite. Slate can be found in many shades of grey, from pale to dark, and may also be purple, green or cyan.
Parliament House - Constructed of grey Kapunda marble on a plinth of grey West Island granite with mottled Angaston marble steps. Note the large bluish porphyritic Kingston granite blocks as seating on King William Road. Make sure to look for the sandstone lion from the British House of Commons on North Terrace, cache background image.
Q1: The block slopes. Using your GPSr estimate the height change of the West Island granite plinth along North Terrace. Compare to the crystal size of the grey Parliament House granite with brown granite at 2 King William St (next stage).
2 King William Street - Ground floor panelling in brown granite from Dromana, Victoria with sawn Waikerie and Ramco limestone ashlar above. Note the Mintaro slate paving used on this corner of the intersection.
Q2: Estimate the crystal size of the brown granite. Compare to the crystal size of the grey Parliament House granite.
Boer War Memorial - Pedestal and base are pink Mannum granite (Earthcache http://coord.info/GC1W73G). Compare the crystal size of this granite to the previous examples.
Q3: Estimate the diameter of the xenolith inclusion on the east face of the base.
Earthcache is based on "The Building Stones of North Terrace - A walk along North Terrace, illustrating the use of stone and other building materials." David Young, SA Department of Mines and Energy, 1986. Details of stone geology and morphology sourced from Wiki.