Calcareous sinter is a freshwater

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

deposit, also known as calc-sinter. Deposits are characterised by low porosity and well-developed lamination, often forming crusts or

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

layers.

Calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

sinter should not be confused with siliceous sinter, which the term sinter more frequently refers to. It has been suggested that the term "sinter" should be restricted to siliceous spring deposits and be dropped for calcareous deposits entirely.

Features

Calcareous sinter is characterised by laminations of prismatic crystals growing perpendicular to the substrate; laminations are separated by thin layers of microcrystalline carbonate. Calcareous sinter is porous due to the calcareous crystals enclosing many small cavities.

Macrophyte Aquatic plants, also referred to as hydrophytes, are vascular plants and non-vascular plants that have adapted to live in aquatic environments ( saltwater or freshwater). In lakes, rivers and wetlands, aquatic vegetations provide cover for aquat ...

s are absent, consequently porosity is very low. Exclusion of species is due either to high temperature (

travertine Travertine ( ) is a form of terrestrial limestone deposited around mineral springs, especially hot springs. It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and rusty varieties. It is formed by a process ...

), high pH/

ionic strength The ionic strength of a solution is a measure of the concentration of ions in that solution. Ionic compounds, when dissolved in water, dissociate into ions. The total electrolyte concentration in solution will affect important properties such a ...

(

tufa Tufa is a variety of limestone formed when carbonate minerals precipitation (chemistry), precipitate out of water in ambient temperature, unheated rivers or lakes. hot spring, Geothermally heated hot springs sometimes produce similar (but less ...

) or absence of light (

speleothem A speleothem (; ) is a geological formation made by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depen ...

s). Pedley (1990) suggests the term be abandoned in favour of tufa for ambient temperature deposits. This avoids any potential confusion with siliceous sinter and prevents deposits formed in different environmental conditions (hot spring deposits, cold spring deposits and speleothems are all lumped together under the term sinter) from being amalgamated into one group.

Geochemistry

Deposits are formed from either

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...

. Precipitation is brought about by degassing of CO₂, which decreases the solubility of calcite/aragonite. (See tufa/geochemistry)

Notable deposits

Pamukkale Pamukkale, () meaning "cotton castle" in Turkish language, Turkish, is a natural site in Denizli Province in southwestern Turkey. The area is famous for a carbonate mineral left by the flowing of Hot spring, thermal spring water. It is located in ...

, Turkey – terraces of travertine. *

Mono Lake Mono Lake ( ) is a Salt lake, saline soda lake in Mono County, California, formed at least 760,000 years ago as a terminal lake in an endorheic basin. The lack of an outlet causes Hypersaline lake, high levels of salts to accumulate in the lake ...

, California - towers of tufa.

Gallery

Image:Kalksinter.JPG, Pure calc sinter, typical for aqueducts and all kinds of water facilities. Image:Eifelwasserleitung05.jpg, Roman aqueduct in

Germania Inferior ''Germania Inferior'' ("Lower Germania") was a Roman province from AD 85 until the province was renamed ''Germania Secunda'' in the 4th century AD, on the west bank of the Rhine bordering the North Sea. The capital of the province was Colonia Cl ...

Eifel Aqueduct The Eifel Aqueduct was one of the longest aqueducts of the Roman Empire. The aqueduct, constructed in AD 80, carried water some from the hilly Eifel region of what is now Germany to the ancient city of Colonia Claudia Ara Agrippinensium (presen ...

, clogged by fine sinter. Image:Travertine-mound_Bridgeport_CA.jpg, Deposits of several thousand years of calc sinter (

) in the

Bridgeport, California Bridgeport is an unincorporated community and census-designated place (CDP) in Mono County, California, United States. It is the county seat of Mono County. The population was 553 at the 2020 census. The first post office at Bridgeport opened i ...

Hot Springs

Medieval extraction and use

The build-up of calc-sinter material in the Eifel Aqueduct was commercially exploited in the 11th and 12th centuries. With deposits up to thick, the material was cut into vertical columns of polished brown rock with impressive layered patterns, which made it much in demand by cathedral builders across large parts of central Europe and beyond. In England it was used to provide polychromy, contrasting with the pale limestone favoured by Norman English Cathedrals. The stone was for many years known as 'Onyx Marble' despite being very obviously neither

onyx Onyx is a typically black-and-white banded variety of agate, a silicate mineral. The bands can also be monochromatic with alternating light and dark bands. ''Sardonyx'' is a variety with red to brown bands alternated with black or white bands. ...

nor

marble Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO3) or Dolomite (mineral), dolomite (CaMg(CO3)2) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is ty ...

. Those studying the stonework at

Canterbury Cathedral Canterbury Cathedral is the cathedral of the archbishop of Canterbury, the spiritual leader of the Church of England and symbolic leader of the worldwide Anglican Communion. Located in Canterbury, Kent, it is one of the oldest Christianity, Ch ...

were unaware of its origins in the aqueduct until 2011. Such large-scale use as the cloisters around a cathedral quadrangle needed many hundreds of columns, which must have been supplied by a well-organised extraction and transport operation. The Eifel deposits, have also been identified at Rochester and in the now lost Romanesque cloister at

Norwich Norwich () is a cathedral city and district of the county of Norfolk, England, of which it is the county town. It lies by the River Wensum, about north-east of London, north of Ipswich and east of Peterborough. The population of the Norwich ...

as well as the Infirmary Cloister, Chapter House windows, Anselm Chapel door and the Treasury gateway at Canterbury.

References