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Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock.
A stone tool is, in the most general sense, any tool made either partially or entirely out of stone. Although stone tool-dependent societies and cultures still exist today, most stone tools are associated with prehistoric cultures that have become extinct. Archaeologists often study such prehistoric societies, and refer to the study of stone tools as lithic analysis. Ethnoarchaeology has been a valuable research field in order to further the understanding and cultural implications of stone tool use and manufacture.
In geology, rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's outer solid layer, the crust, and most of its interior, except for the liquid outer core and pockets of magma in the asthenosphere. The study of rocks involves multiple subdisciplines of geology, including petrology and mineralogy. It may be limited to rocks found on Earth, or it may include planetary geology that studies the rocks of other celestial objects.
Amphibolite is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance.
Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals. These minerals form as a result of alteration which occurs when hydrothermal fluids interact with a protolith of either igneous or sedimentary origin. In many cases, skarns are associated with the intrusion of a granitic pluton found in and around faults or shear zones that commonly intrude into a carbonate layer composed of either dolomite or limestone. Skarns can form by regional, or contact metamorphism and therefore form in relatively high temperature environments. The hydrothermal fluids associated with the metasomatic processes can originate from a variety of sources; magmatic, metamorphic, meteoric, marine, or even a mix of these. The resulting skarn may consist of a variety of different minerals which are highly dependent on both the original composition of the hydrothermal fluid and the original composition of the protolith.
The Langdale axe industry is the name given by archaeologists to a Neolithic centre of specialised stone tool production in the Great Langdale area of the English Lake District. The existence of the site, which dates from around 4,000–3,500 BC, was suggested by chance discoveries in the 1930s. More systematic investigations were undertaken by Clare Fell and others in the 1940s and 1950s, since when several field surveys of varying scope have been carried out.
Merrivale is a locality in western Dartmoor, in the West Devon district of Devon, England. It is best known for the nearby series of Bronze Age megalithic monuments to the south and a former granite quarry.
Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. These properties are due to fine grained non-aligned crystals with platy or prismatic habits, characteristic of metamorphism at high temperature but without accompanying deformation. The term is derived from the German word Hornfels, meaning "hornstone", because of its exceptional toughness and texture both reminiscent of animal horns. These rocks were referred to by miners in northern England as whetstones.
Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically 300–450 °C (570–840 °F) and 2–10 kilobars (29,000–145,000 psi). Greenschists commonly have an abundance of green minerals such as chlorite, serpentine, and epidote, and platy minerals such as muscovite and platy serpentine. The platiness gives the rock schistosity Other common minerals include quartz, orthoclase, talc, carbonate minerals and amphibole (actinolite).
Australian Aboriginal artefacts include a variety of cultural artefacts used by Aboriginal Australians. Most Aboriginal artefacts were multi-purpose and could be used for a variety of different occupations. Spears, clubs, boomerangs and shields were used generally as weapons for hunting and in warfare. Watercraft technology artefacts in the form of dugout and bark canoes were used for transport and for fishing. Stone artefacts include cutting tools and grinding stones to hunt and make food. Coolamons and carriers such as dillybags, allowed Aboriginal peoples to carry water, food and cradle babies. Message sticks were used for communication, and ornamental artefacts for decorative and ceremonial purposes. Aboriginal children’s toys were used to both entertain and educate.
Aboriginal stone arrangements are a form of rock art constructed by Aboriginal Australians. Typically, they consist of stones, each of which may be about 30 centimetres (12 in) in size, laid out in a pattern extending over several metres or tens of metres. Notable examples have been made by many different Australian Aboriginal cultures, and in many case are thought to be associated with spiritual ceremonies.
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in the geological history of the area. The boundaries between facies are wide because they are gradational and approximate. The area on the graph corresponding to rock formation at the lowest values of temperature and pressure is the range of formation of sedimentary rocks, as opposed to metamorphic rocks, in a process called diagenesis.
The Florisbad archaeological and paleontological site is a provincial heritage site in Brandfort in the Free State province of South Africa. The most notable find at this site is the Florisbad Skull, the partial skull of an early human species that was discovered in 1932.
The Massachusetts Hornfels-Braintree Slate Quarry is a prehistoric archaeological site in Milton and Quincy, Massachusetts. It consists of a series of pits and trenches used from 7,000 B.P. until the early 17th century as a source of slate and hornfels used for chipped and ground tools. Pieces made from material quarried at the site are found over much of eastern Massachusetts. The site was added to the National Register of Historic Places in 1980.
Wurdi Youang is the name attributed to an Aboriginal stone arrangement located off the Little River – Ripley Road at Mount Rothwell, near Little River, Victoria in Australia. The site was acquired by the Indigenous Land Corporation on 14 January 2000 and transferred to the Wathaurong Aboriginal Co-operative on 17 August 2006.
The Mount William stone axe quarry is an Aboriginal Australian archaeological site in Central Victoria, Australia. It is located 9 kilometres (5.6 mi) northeast of Lancefield, off Powells Track, 10 kilometres (6.2 mi) north of Romsey and 78 kilometres (48 mi) from Melbourne. Known as Wil-im-ee moor-ring, meaning "axe place" in the Woiwurrung language, the greenstone quarry was an important source of raw material for the manufacture of greenstone ground-edge axes, which were traded over a wide area of south-east Australia.
Aboriginal sites of Victoria form an important record of human occupation for probably more than 40,000 years. They may be identified from archaeological remains, historical and ethnographic information or continuing oral traditions and encompass places where rituals and ceremonies were performed, occupation sites where people ate, slept and carried out their day to day chores, and ephemeral evidence of people passing through the landscape, such as a discarded axe head or isolated artefact.
Tachylite is an unusual and relatively rare stone used in making flaked stone tools, and which is found in Aboriginal archaeological sites in Victoria, Australia.
Caroline Bird is an Australian archaeologist and educator. She specialises in women's studies, cultural heritage, and indigenous studies in the archaeological context, specifically early Australian archaeology. Bird's other focuses include lithic technology and art.
References
- ↑ A Record In Stone: The Study Of Australia's Flaked Stone Artefacts By Simon Holdaway, Nicola Stern
- ↑ Archaeological survey of Aboriginal chert hornfels quarry sites in eastern Tasmania: a report for the Australian Heritage Commission / David Rhodes, Ian Thomas, Melbourne, Vic. Du Cros and Associates, 1994
- ↑ Archaeological Survey of Gravel Search Area Victoria Highway [ permanent dead link ]
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