Neuburg siliceous earth

Neuburg siliceous earth is a natural mixture with dominant fractions of ultra-fine silica particles and 20 to 40 percent by weight kaolinite. The International Mineralogical Association does not recognize it as a mineral in its own right.
The only known deposits with this composition are found near Neuburg an der Donau, Bavaria, Germany.
It is a purely mineral formation, as contrasted with typical siliceous earth or diatomaceous earth, which have biological origins and were developed from diatoms.
Neuburg siliceous earth is used as a functional filler or as a polish in industrial applications. It is also used as a dietary supplement.
Geology
Neuburg siliceous earth was formed about 93 to 98 million years ago in the Cenomanian lowest stage of the Upper Cretaceous in a bay that was located in today's occurrence area, as the finest sediments were deposited from weathered granitic masses of the Northern Upper Palatinate.
The index fossil associated with these sediments is Inoceramus crippsi.
Mineralogy
Neuburg siliceous earth was probably formed as a mixture of minerals. It essentially consists of very fine crypto-crystalline particles (appearing amorphous, particles smaller than one micrometer) and amorphous silicic acid with a total of 60 to 80 percent by weight, and the rest consists of lamellar (flaky) kaolinite. Contrary to previous assumptions, the silicic acid fraction is not composed of quartz, since the basic characteristics of quartz are lacking, but rather a special SiO<sub>2</sub>-modification.
Finding natural mineral deposits
Neuburg siliceous earth is found in funnels and run-ins in the underlying Jura limestone. Near-surface deposits were undoubtedly already discovered long ago, since they are sometimes only covered by a thin layer of soil. The deposits still remaining today are generally found under young geological layers at a depth of five to twenty meters. In the past, exploration was achieved by taking cores with manual devices. Today, machine drilling continuously produces crushed borehole cuttings at much lower costs, whereby the siliceous earth can be easily distinguished from the soil and limestone on-site and without special analysis.
Mining
Romans used Neuburg siliceous earth for fireproof linings in kilns for pottery. Around 1830 the material began being specifically extracted again after chemists discovered a formula for producing the extremely expensive pigment ultramarine blue, for which Neuburg siliceous earth is a natural raw material.
Until well into the 19th century, the near-surface deposits were extracted mainly from open-pit mines. Beginning at the end of the 19th century, mineral deposits were increasingly exploited through underground mining, since it was often easier to dig through thicker layers of soil than to remove it completely. When mining underground, however, large portions of the deposits could not be used, since valuable material had to remain intact for structural reasons.
The last extraction sites operated underground were closed in 1979 and all current extraction uses open-pit mines. With modern surface mining, excavators rapidly remove the overburden layers and quarry out the raw material. Blasting is rarely necessary.
In 2015, 55,000 tons of the purified mineral were produced. This required the extraction of 120,000 t of raw siliceous earth using open-pit mining.
the only company that mines the material has been Hoffmann Mineral GmbH.
Mitigation of mining effects
Once the mining operations in a deposit have ceased, the large craters are filled with excavation material and with sands and other rocks that were separated during purification of the extracted material. Humus layers are then spread on top. Ecologically valuable wetlands are sometimes created during the course of the mining operations. Such biotopes are preserved after mining operations have ceased, and offer a habitat and spawning grounds for various species including yellow-bellied toads (Bombina variegata), European tree frogs (Hyla arborea), smooth newts (Lissotriton vulgaris), Alpine newts (Ichthyosaura alpestris) and crested newts (Triturus sp.), although none of these species are classified as threatened by IUCN criteria.
Purification
First, the raw material is suspended in well water. The usable finest fraction is extracted in successive physical separation processes by centrifuging in hydrocyclone. Afterwards, the excess water is re-separated and pressed out, and finally the material concentrated on moist filter cakes is dried in a natural gas-powered turbine dryer to produce its powdery final quality.
About 45% (by mass) of the excavated material is extracted and sold as the final product. The rest is tailings.
Use
Neuburg siliceous earth is mainly used today as a filler for polymers. This application became popular in the 1920s with the widespread introduction of rubber goods. The loose powder is most notably distinguished by its good miscibility and small grain size. Automobile hoses, floorings and roof sheeting for the construction sector contain high fractions of this filler. In the paint and coatings industry, electrophoretic painting and anti-corrosion coatings are important fields of application.

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