| Basalt | is a dark-coloured, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill. (Wikipedia) | ||||
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| Chalcedony | SiO2- a cryptocrystalline form of silica. Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors. | ||||
| In Hobart it is usually ochre-coloured, with conchoidal fracture | |||||
| Clast | A rock fragment or grain resulting from the breakdown of larger rocks. | ||||
| Clay Balls | Clay balls. During wet weather, lumps of very stiff, tenacious can clay slide down into adjacent water and loose pieces are moved back and forth, over either a clay or a sandy base, gradually getting smaller and smaller in the process until entirely wasted away. As they roll over and over, the projecting parts, naturally, are worn away fastest and the lump assumes a spherical form. | (source ‘Formation of Clay Balls - https://www.journals.uchicago.edu/doi/pdf/10.1086/623394 ) | |||
| Conchoidal Fracturing | A fracture with smooth, curved surfaces that resemble the interior of a seashell; it is commonly observed in quartz and glass - and is characteristic fracture form of dolerite and basalt | ||||
| Dip | The angle at which a layer/bed/grain of rock is inclined to the horizontal. | ||||
| Dolerite | A type of dark rock that comes from magma (= very hot liquid rock that has cooled). It has crystal grains that are usually visible to the naked eye. | ||||
| Dropstones | Glacial dropstones are rocks fallen out of icebergs and deposited in low-energy deep sea environments. When dropped into fine-layered mud the stones create impact depressions, and mud squeezes up around the edges of the falling rock. Subsequent deposits of mud can then drape over the dropstone and its crater. | https://en.wikipedia.org/wiki/Glacier | |||
| Exfoliation Weathering | physical pressure-release exfoliation mechanism by which igneous and metamorphic rocks are broken down. See illustration below. | https://www.geologyin.com/2025/12/spheroidal-vs-exfoliation-weathering.html | |||
| Gondwana | was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia, Zealandia, Arabia, and the Indian subcontinent. | ||||
| Gondwana 420 million years ago (late Silurian). (Wikipedia) | |||||
| Graben | A (geological) graben is a depressed block of the crust of a planet, bordered by parallel normal faults. | https://en.wikipedia.org/wiki/Graben | |||
| Igneous | Igneous (intrusive; extrusive/volcanic). Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive (volcanic) rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses. | ||||
| Lapilli (volcanic) | Lapilli are usually irregular or angular in shape due to violent magma fragmentation but can be spherical, teardrop, dumbbell, or button shaped droplets if more fluid. | ||||
| They are typically molten or partially molten lava ejected from a volcanic eruption that fall to earth as solid or partially molten rock. Lapilli that forms from this process usually becomes pumice if felsic or scoria if mafic. These granules are the direct result of liquid rock cooling as it travels through the air. (Wikipedia). NB- Tasmanian volcanice didnt produce ‘pumice’. | |||||
| Lapilli is a size classification of tephra, which is material that falls out of the air during a volcanic eruption | |||||
| Matrix | The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded. (Wikipedia) | ||||
| Mudstone | Rock composed of clay-to-mud sized material. | ||||
| Mya | Million years ago | ||||
| Permian–Triassic extinction event | The Permian–Triassic extinction event occurred occurred approximately 251.9 million years ago (mya), at the boundary between the Permian and Triassic geologic periods. It is Earth's most severe known extinction event, with the extinction of 57% of biological families, 62% of genera, 81% of marine species and 70% of terrestrial vertebrate species | ||||
| Plate - Australian | The Australian plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately 100 million years ago when India broke away and began moving north. Australia and Antarctica had begun rifting by 96 million years ago and completely separated a while after this 60-45 Mya | ||||
| Plate - Tectonic | (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. The surface of the Earth is divided into 7 major and 8 minor plates. The largest plates are the Antarctic, Eurasian, and North American plates. Plates are on average 125km thick, reaching maximum thickness below mountain ranges. Oceanic plates (50-100km) are thinner than the continental plates (up to 200km) | https://pubs.usgs.gov/gip/dynamic/tectonic.html | |||
| Sandstone | Sedimentary rock composed of sand-sized particles. | ||||
| Spheroidal Weathering | Characteristic of weathered dolerite. | https://www.geologyin.com/2025/12/spheroidal-vs-exfoliation-weathering.html | |||
| Tephra (volcanic term) | Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. | ||||
| Tephra fragments are classified by size: | |||||
| Ash – particles smaller than 2 mm (0.08 inches) in diameter | |||||
| Lapilli or volcanic cinders – between 2 and 64 mm (0.08 and 2.5 inches) in diameter | |||||
| Volcanic bombs or volcanic blocks – larger than 64 mm (2.5 inches) in diameter | |||||
| Trace-fossils. | Trace fossils are defined as biological traces, such as burrows, tracks, and feeding scrapes, that are preserved in sediment that eventually hardens into rock, often remaining even when the organism that created them has disappeared. (source | https://www.sciencedirect.com/topics/earth-and-planetary-sciences/trace-fossil ) | |||
| Tuff | Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. | ||||
Spheroidal vs. Exfoliation Weathering
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