Sharpening history. Cambrian Green stone

The Cambrian Green stone gets its name from one of the layers of a shale quarry being developed in the Area of Llyn Idwal lake in Wales, UK. For the first time, the deposit in the lake area was reported by the famous Irish scientist Richard Kirwan at the end of the XVIII century. He pointed out that there was a large quarry of novaculite in this place, from where the rock was cut out and transported to London and Dublin. 

Novaculite is commonly called siliceous shale, which is formed by aggregates of randomly oriented polyhedral quartz grains of the same or similar size with sharp boundaries between the grains. Novaculites include, for example, the Arkansas stones.

Llyn Idwal is a small lake measuring 800x300 m, located in the Glyderau mountains in Snowdonia. These mountains are part of the Cambrian Mountains system, a series of plateaus in the United Kingdom that separate Wales from England and occupy the main part of the Welsh Peninsula. 

The highest point is the mountain Plynlimon Fawr 752 meters high. The total length of the Cambrian mountains is about 60 kilometers. They contain a mixture of volcanic rocks and sedimentary rocks from the Cambrian to Ordovician period and are formed from Ordovician and Silurian sandstones and mudstones (clay sedimentary rocks), which in many areas come to the surface.

Sandstones were formed as a result of the destruction of rocks, the transfer of debris by water or wind, and deposits followed by cementation. Most varieties of sandstones are dominated by quartz, as the most stable physically and chemically mineral. Based on quartz, siliceous shale (hornstone) is formed — a sedimentary rock with a clearly defined stratification. The rock layers are formed by cryptocrystalline or micrograined quartz or chalcedony with an admixture of clay material. The reason for the formation of these ancient Paleozoic sedimentary rocks was the diagenetic crystallization of radiolarian and diatomic algae matter. The color of siliceous shales is usually reddish-brown, but various impurities can color it gray or black. However, a large amount of iron in the rock can also give a fairly rich green color to the stone, which is obviously what happened with the Cambrian Green stone.

Cambrian Green stone has a fairly dense structure and at the same time a pronounced layering. The approximate hardness of the stone on the Mohs scale is about 4 units. It is slightly softer than Arkansas, but it is superior in hardness to Belgian and French sharpening stones and has greater wear resistance. Also, one of the distinctive properties of the stone is the characteristic metallic gleam. The color scheme varies from dark green to dark gray, and there are quite a lot of white dots on its surface, left over from frozen air bubbles. Externally, Cambrian Green is very similar to the famous Turkish stone (see the article). When working, it gives a milky chlorite suspension. 

This suspension is initially very small in size and is extremely slow to break up. The stone works with water and water-based coolants. Experienced sharpeners estimate its grain size in the range from 2000 to 3000 grit according to the FEPA-F system. The quality of stone work strongly depends on the surface of the processed product, pressure, dryness of the suspension, density, fragmentation (the duration of work on the suspension without updating). It works softer than Belgian stones, in particular, Belgian Blue Whetstone and Yellow Coticule. The stone can be used as a finishing stone for knives and a pre-finishing stone for razors. For preparing Cambrian Green for work, you can use the 1200th silicon carbide powder. As a result, you can get a mat surface, but with a fairly large number of deep marks. The cutting edge after finishing with this stone has fineness and sufficient aggression. The stone shows itself as well as possible when working on solid powder steels and carbon-based solid quick-speed steels. 

The Cambrian Green stone is one of the most famous English sharpening stones, competing with the Dragon Tongue and Charnley Forest. Stone is represented on the market of sharpening products in a fairly large number, but at the moment there is no information about its systematic extraction. In the quarries of Wales today, under the name "Cambrian Green", so-called "Cambrian boulders" are mined, which are a mixture of angular and roughly rounded stones in shades of gray, black, green, and brown. 

They are mainly used for landscape design and creation of water objects: artificial ponds, fountains, etc. And if the mining of sharpening stone stops, then the reserves of Cambrian Green stone will gradually be depleted and the stone will go into the past, becoming part of the sharpening history.