Historical information

Feldspathic arenites are sandstones that contain less than 90% quartz, and more feldspar than unstable lithic fragments, and minor accessory minerals.Feldspathic sandstones are commonly immature or sub-mature.These sandstones occur in association with cratonic or stable shelf settings. Feldspathic sandstones are derived from granitic-type, primary crystalline, rocks. If the sandstone is dominantly plagioclase, then it is igneous in origin

Sandstone features prominently in public buildings throughout Victoria. Most of the sandstone used as dimension stone in the State came from three sources: the Heatherlie quarry in the Grampians (Silurian), the Bacchus Marsh area (Permian), and the Barrabool Hills near Geelong (Cretaceous).

Significance

This specimen is part of larger collection of significant geological specimens in the Burke Museum that was collected from around the world between 1868-1880. A large percentage of these specimens were collection as part of the Geological Survey of Victoria 1852-1974. The Geological Survey of Victoria was an organisation founded in response to the Victorian gold rush to explore the geological and mineral resources and to record a detailed map of the state. It was headed by British geologist, Alfred Richard Cecil Selwyn (1824-1902), who was responsible for issuing over 60 geological maps during his 17 years as director. These maps were all hand-drawn and coloured and became the benchmark for accuracy for geological mapping. Collecting geological specimens was an important part of mapping and understanding the scientific makeup of the earth. Many of these specimens were sent to research and collecting organisations across Australia, including the Burke Museum, to educate and encourage further study.

Sandstone features prominently in public buildings throughout Victoria, making this specimen special as it shows the materials used by Victorian building companies. Sandstone can also be crushed, crushed stone is used in the construction of roadways and road structures such as bridges, and in buildings, both commercial and residential.

Physical description

A feldspar-rich sandstone, a sandstone intermediate in composition between an arkosic sandstone and a quartz sandstone, containing 10% to 25% feldspar and less than 20% matrix material of clay, sericite, and chlorite.

Feldspathic arenite containing less than 90 percent of the composition of quartz. Feldspar is the main composition. Feldspathic arenite may contain fragments of unstable rock, and a little amount of other minerals such as mica and heavy minerals. Some feldspathic arenite have pink or red color because of the presence of potassium feldspar or iron oxide. There are also colored light gray to white. These sandstones are usually medium to coarse grained and can contain a high percentage of granules with angular until subangular roundness. The content of the matrix can appear as the rest up to more than 15 percent, and sorting of grains can present as moderate to poorly sorted. Feldspathic sandstones are generally immature in textural maturity. Feldspathic arenite can not be judged from the structure of the sediment. Bedding can emerge from the laminate parallel to the crossbed. Fossils may appear in the layer deposited on the sea. Feldspathic arenites usually appear on the craton or the continental shelf, which can be associated with conglomerate, quartz lithic arenite, carbonate rock, or evaporites. This sandstone may also appear on the succession of sedimentary basins deposited on an unstable or deep sea, and moving arc setting. According to Pettijohn (1963) Arkose make up about 15 percent of all sandstones. Some Arkose formed in situ when the granite and related rocks disintegrate and generate granular sediments. Most of the material feldspathic sandstones derived from primary crystalline granitic rocks, such as granite or metasomatic rocks containing abundant potassium feldspar. Mineral contained in sandstones is mostly a form of plagioclase feldspar derived from quartz diorite or volcanic rock. Feldspar contained on this sandstone comes from arid to cool climates when the chemical weathering process is reduced.