Novaculite

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Black Arkansas Stone

Novaculite (from Latin novacula = sharp knife, razor) is a very fine-grained metamorphic pebble . The material is mainly used for whetstones . It is best known as Arkansas stone or Washita stone and is mined in this form in the USA.

Rock and formation

Novaculite is a chert , and thus a hard, isotropic rock of white to black-gray color and sedimentary formation. It consists of cryptocrystalline quartz ( silicon dioxide ), subordinate also of chalcedony and small amounts of feldspar and garnet , and shows a shell-like break with sharp edges. Like kieselguhr or flint on the lake or sea floor, novaculite was created from the remains of organisms with silicic acid skeletons, such as those found in diatoms , or from other silicic acid-rich residues such as the needles of silica sponges . In the course of the diagenesis , the silica was enriched through solution transport in tubers and layers. In contrast to flint, the novaculite underwent a further structural change during a pressure-stressed metamorphosis , which led to a thorough recrystallization, which produced a fine, homogeneous microstructure .

Occurrence

Novaculite is found primarily in the Ouachita Mountains in Arkansas and Oklahoma in the United States . Here the parent rock was deposited in the Devonian , in the Carboniferous the metamorphic rock formed through a pressure-stressed metamorphosis during the formation of the Ouachita Mountains. Other deposits can be found in Texas in the Caballos Novaculite of the Marathon Uplift .

Dismantling and use

The rock is mainly mined in Arkansas in Garland and Hot Spring Counties . Since it is very brittle, no blasting is used to mine it, it is cut with diamond saws and ground using abrasives such as silicon carbide .

The rock was used in arrow or spearheads by the Native Americans because of its excellent properties. Today it is used exclusively as a natural whetstone.

In trade it is sold under the name Arkansas stone - extremely fine-grained, typically cloudy-white or light gray to black-gray, with a waxy sheen - or Washita stone - similarly hard, somewhat coarser in the grain and often more colored. The stone is always used with a little petroleum or odorless lamp oil (hence the name 'oil stone') when sharpening knives, tools and surgical instruments , the use of water quickly clogs the surface and is therefore unsuitable. An exception to this is the rare milky-white soft Arkansas, which is available in a somewhat coarser form, on which you can also work with water if necessary. There are many different Arkansas stone variants. They usually have a grain size of around 6000 to 8000 JIS and do not form any grinding sludge ('paste'). As they are very hard, they are, unlike other natural whetstones, subject to little wear and tear and keep their shape for a long time. As a rule, the black and glassy stones are denser than the white ones.

See also

Individual evidence

  1. ↑ PB King: Geology of the Marathon Region, Texas ( Memento of the original from April 24, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , United States Geological Survey Professional Paper 187, Boulder 1937 @1@ 2Template: Webachiv / IABot / www.lib.utexas.edu

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