Sharpening story. Bentheimer Sandstone

One of the oldest sharpening stones in Europe – Bentheimer Sandstone began to get developed in the first quarries from about 1250. Since then and up to the 50s of the XX century, it was one of the most popular and prestigious building materials and had high popularity as a sharpening stone.

The sandstone deposit was located in the German county of Bentheim, in the state of Lower Saxony, located in northwestern Germany on the border with Holland. Sandstone mining in this region reached its peak in the XVII century when 9 quarries were working at once. The material extracted here was so pure that it became an international standard of quality for a long time. For its light yellow color, it was called "Bentheim gold". It was used for buildings in Amsterdam, in particular one of the royal palaces, and in some other Dutch, German and Belgian cities. In churches, it was present in the form of altar tables, portals, and fonts. And in the XIX century, it was used to create the base of the Statue of Liberty, made in France and installed in New York. Bentheimer Sandstone was also actively used in the manufacture of stairs, tombstones, foundations, supporting walls of mills, sculptures, and other objects. In addition, it has gained considerable popularity in Germany and the surrounding lands as a sharpening stone.

Quartz sandstones are the final product of the evolution of sand, when sedimentary differentiation and chemical weathering led to the formation of almost monomineral quartz rocks, in these sands the quartz content is 95% or higher. To date, the Bentheimer Sandstone is the reference for this rock in its composition and internal structure. It was formed in the Lower Cretaceous period 125 million years ago when the territory of Lower Saxony was covered by the sea. Sandstone is the remains of ancient fossilized plants, converted over millions of years into calcium carbonate. In the Bentheim County area, there was shallow water and this erosional sand from mountain rivers was deposited on the shoreline and hardened over time. During the Upper Cretaceous period (70-90 million years ago), the sands experienced a strong tectonic impact and the destruction of the upper layers. The inner, most solid layers that emerged to the surface formed an array of sandstone with a thickness of 60-70 meters, stretching from east to west for about 9 km. This massif comes to the surface in the east of the city of Bad-Bentheim.  

Bentheimer Sandstone outcrop samples are considered ideal for laboratory studies because of their horizontal continuity and block uniformity. For many years, this particular field has been used for scientific research of reservoirs and the study of the movement of gases, oil, and groundwater in them. Bentheimer Sandstone is a rock that consistently exhibits permanent mineralogical properties and is largely free of paramagnetic impurities. It has a porosity of 0.21 to 0.27 cubic meters and permeability of 0.52 to 3.02 Darcy (D and d). Density 2120 kg/m3 - 2400 kg/m3, water absorption is about 7.1% by weight. The friction resistance is 16.4 cm3/50 cm2.

Bentheimer Sandstone was divided during mining into two grades Gildehauser and Bentheim itself: 

Gildehauser - a stone of yellowish, gray, and white colors.

The Bentheimer Sandstone is yellowish-brown and/or redder in color than the Hilderhauser Sandstone and has a greater hardness. Sometimes the so-called "Lisegang rings" are found in the rock, forming brown lines. Such formations occur in the layered structure of thin-porous rocks during weathering processes. Among them are rhythmic rings, bands, and hyperbolas colored with brown iron hydroxides. Bentheim has a homogeneous structure and large quartz grains.

The main abrasive for the work of the stone is quartzite. The rock-forming minerals are quartz, feldspar, mica, and glauconite. Rock fragments may also be present. Secondary and accessory (impurity, which makes up a very small amount) minerals are usually represented most often by magnetite, ilmenite, garnet, rutile, zircon, tourmaline. The substance that cements the detrital material is relatively pure clay (hydromica, kaolinite, etc.), calcareous (calcite, dolomite, rarely ferruginous carbonates), siliceous (opal, chalcedony, quartz), ferruginous (oxides and hydroxides of iron), sometimes chlorite, zeolite, phosphate, sulfate or mixed.

The stone was used mainly for working with water, in the form of large heavy grinding wheels with a pallet. It was used primarily for sharpening various tools. There are few memories about the quality of the work of the stone in sharpening. Sandstones are traditionally graded as 2000-5000 grit according to the JIS system, depending on the number of impurities. They are used with water, both with soaking and without soaking the stone. Sandstones are considered fast enough stones, but they are more suitable for pre-finishing sharpening and require the use of a fine stone for finishing the blade after. The main disadvantage of Bentheimer Stone, as well as any sandstone, was its fragility and tendency to chip.

Despite the popularity of the stone and the exceptional quality of the rock, its use was banned in 1951, due to its harmful effects on health. It was found that the use of stone and especially its extraction cause problems with the lung tissue. Workers began to detect silicosis - a lung disease caused by the inhalation of free silicon dioxide, the main distributor of which was quartz dust. In 2005, the use of sandstone was allowed, with strict use of protective equipment by employees. In modern times, there is only one quarry in Bentheim. The stone is used for the restoration of buildings constructed from it in the past. In addition, Bentheim has had a museum dedicated to the history of its main attraction, the "Bentheim Golden Sandstone", for many years.