Blue Mountains Basalts are

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

rocks occurring in the Sydney Basin in eastern Australia. This formation is up to 140 metres thick. Formed in the middle

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

, some 17 million to 14 million years ago. The remnants of this

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

lava flow are confined to the higher altitudes in the western Blue Mountains. Such as Mount Hay, Mount Wilson, Mount Irvine,

Mount Banks Mount Banks, a mountain within the Explorers Range of the Blue Mountains Range that is a spur off the Great Dividing Range, is located within the Blue Mountains National Park, approximately west of Sydney in New South Wales, Australia. Mount ...

and Mount Tomah. The

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

basalt caps create red/brown soils, known as red podzolics or ''krasnozems''. They have been exposed to a considerable degree of chemical weathering, with a higher iron-oxide concentration than with

podzol In soil science, podzols are the typical soils of coniferous or boreal forests and also the typical soils of eucalypt forests and heathlands in southern Australia. In Western Europe, podzols develop on heathland, which is often a construct of ...

s, hence the reddish colour. Vegetation on these basalt based soils are associated with rainforest, moist

eucalyptus ''Eucalyptus'' () is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with several other genera in the tribe Eucalypteae, including '' Corymbia'', they are commonly known as e ...

forest and the tourist attraction gardens at Mount Wilson and the

Blue Mountains Botanic Garden The Blue Mountains Botanic Garden, originally known as the Mount Tomah Botanical Garden, is a public botanic garden located approximately west of the Sydney central business district at in the Blue Mountains, in New South Wales, Australia. Th ...

. These basalt cap soils have a higher level of moisture retention and fertility than the more common

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

based soils in the Blue Mountains. The original

volcanic plug A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of high gas pressure if rising volatile-charged ma ...

s have yet to be discovered, due to the considerable amount of erosion this rock layer has experienced. Geologists have determined that the Blue Mountains Basalts are derived from a lava flow, not a volcanic plug. The remnant basalts were formed from a

viscous The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

fluid flow of

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

, not a vertical inner core of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

as with an eroded volcano.https://www.geocaching.com/geocache/GC2HFV5_blue-mountains-basalt-capping?guid=aeeb9fb9-3cc3-45f4-a4a8-95b0f31d95c6 Geocaching - Blue Mountains Basalt Capping, retrieved May 29, 2016

References

{{Reflist Geology of New South Wales Geography of the Blue Mountains (New South Wales)

See also

References