Operating masses need to have an individual and precisely defined grain size distribution for efficient processing. A medium grain framework and a support grain framework of d > 63 µm should be guaranteed besides the necessary finest fraction d < 2 µm. Type and fraction of the sieving residues have a significant influence on the processing and product properties. Advantages can be found during drying and degassing in the tunnel furnace. Disruptive are solid aggregates of carbonates and sulfates / sulfides as well as certain oxides and hydroxides. They can lead to spalling. To much quartz causes heating and cooling cracks.
In the sieving residues of plastic clays weathering resistant remains of the source rock which have been deposited together with the clay can be found. They mostly consist of quartz, feldspar, micas and rock fragments. Plant remains, coal fragments and microfossils can be additional parts of the detritus. Often large amounts of weathering products like hematite and goethite are enriched in the sieving residues.
Furthermore sedimentary and diagenetic new formations like glauconite, pyrite and argillaceous ironstone geodes can be found. For diagenetic and metamorphic claystones a large amount of dispersible cemented clay particles in the sieving residue is characteristic. Clay marl and evaporitic imprinted clay layers are characterized by aggregates of calcite, dolomite and gypsum.
Rock dust / fillers are pulverized mineral products with a delivery grain size of 0/90 µm. A fine sandy over size fraction up to d = 200 µm is characteristic. Rock dust / fillers are produced as a by-product of natural stone processing and can be used as temper in the brick industry. Petrographically they mostly consist of plutonites and vulcanites. Smaller amounts are produced during processing of metamorphic and sedimentary solid rocks.
are products of crystallization from siliceous melts. They make up about 70 vol.-% of the earth’s continental crust. Plutonites crystallize in layers of > 5 km depth in bis magma chambers during slow cooling. They usually have medium to coarse grain sizes and show now textural effects. Plutonites are exposed on the earths surface after tectonic uplift or profound erosion usually millions of years after their formation. In the sieving residue broken crystals, often with rounded edges, of idiomorphic to xenomorphic shape can be found. The melting point and the sintering interval are largely controlled by the amount of silicic acid. The following types are of potential interest for the brick and tile industry:
Syenite is often coloured light grey to red, but it can also occur in dark colour. The fabric is holocrystalline and directionless granular. Syenite consists almost exclusively of alkali feldspar (orthoclase and microcline). The amount of sodium-rich to intermediate plagioclase is consequently low. Quartz is largely absent. Mafic minerals like biotite, hornblende, pyroxene and olivine occur only in small quantities.
Leukokrates, mittel- bis grobkörniges massiges Gestein mit überwiegend hellen Gemengteilen, bestehend aus Quarz, Kalifeldspat und Plagioklas (Anorthit < 30 MA %). Zu den mafischen Gemengteilen zählen Muskovit und BiotLeucocratic, medium to coarse grain massive rock with predominantly bright components consisting of quartz, potash feldspar, plagioclase (anorthite < 30 MA %). Mafic components are muscovite and biotite, more rarely also hornblende, pyroxene and tourmaline. Accessory components can be zircon, titanite, apatite and opaque minerals like magnetite and ilmenite. The fabric is holocrystalline and mostly directionless granular. Granitic melts form by magma differentiation in the earth’s continental crust. The differentiation follows the scheme from increasing silicic acid content and decreasing mafic content:
peridotite – gabbro – diorite – granodiorite - granite.
Granite is the typical and most widely spread plutonic rock of the continental crust. The genesis is complex. It is distinguished between: i-type granite = formed by melting of magmatic rocks, s-type granite = formed by melting of sedimentary rocks, a-type granite = formed by rupture of continental crust outside or post orogenic of mountain forming processes.
Granodiorite, similar to Granite is dominated by quartz, feldspar and mica. The transformation from granite to granodiorite is characterized by the modal increase of plagioclase compared to potash feldspar. The increase of plagioclase coincides with an increase of biotite, hornblende and pyroxene. The texture and genesis of granodiorite are mostly equivalent to granite. The rock is massive, middle to coarse grained and of greyish-white to grey colour.
Greyish-green mostly fine to medium grained mesocratic rock of massive structure. The content of bright minerals is dominated by plagioclase (anorthite = 30 – 50 MA %). Potash feldspar and quartz are mostly absent or occur only accessory with less than 5 MA %. Mafic minerals are hornblende, pyroxene and biotite. The fabric is hypidiomorphic granular. With high quartz content the rock is called Quartz Diorite.
Melanocratic to mesocratic middle to course-grained massive rock with piopside and plagioclase (anorthite = 50 – 90 MA %). Only in exceptional cases with low contents of quartz and potash feldpsar. Dark minerals are mostly pyroxenes, hornblende and biotite are absent. If olivine is present the rock is called Olivine Gabbro. Transitions to peridotite start with this type of rock.
Gabbro forms especially in the area of mid-ocean ridges by slow crystallisation of rising basaltic mantle material below the ocean floor.
Holomelanocratic middle to coarse-grained rock consisting almost exclusively of monocline and orthorhombic pyroxene and olivine. Accessory chrome spinel and magnetite can occur. Feldspar and other bright constituents are absent. Peridotite is the typical rock from the earth’s mantle. Because of the very high melting point (> 1400 °C) peridotites usually only come to the earth’s surface by plate tectonic processes / obduction. In the presence of water magnesium-rich minerals are transformed into greenish-black serpentine. If the mantle rock consists almost exclusively of olivine it is called Dunite. Harzburgite represents Dunite with admixtures of orthopyroxene.
are characterized by the rise and intrusion of the magma as far as the near-surface interlaminar bonding or by the outflow and degassing of the magma at the earth’s surface. They make up about 20 vol. % of the earth’s continental crust. As a result of the fast cooling, the microstructure of the volcanites is generally more finely grained than the deep-seated rocks. Volcanic rocks often have a porphyric microstructure, in which larger developed “phenocrysts“ are embedded in a finegrained, sometimes even glassy matrix. Besides erupting liquid lava, most volcanoes emit solid material that is ejected explosively. These loose materials sediment on the earth’s surface as pyroclastic rocks. Depending on the grain size, a differentiation is made between volcanic blocks, lapilli and
ashes. In the ceramic industry the following volcanic rock types are predominantly used:
Leucocratic, dense to fine-grained rock with occasional phenocrysts. Rhyolite consists predominantly of quartz and feldspar, with potash feldspar and plagioclase occuring in complementary amounts. The rock colour is usually bright for example light grey, light green or light red. Dark minerals such as biotite are only rarely interspersed. Rhyolitic melts form by magmatic differentiation in exceptionally thick earth crust beneath continents. With increasing content of silicic acid the following scheme applies:
Tholeiite basalt - andesite - dacite - rhyodacite - rhyolite.
The matrix is often glassy, i.e. not crystalline, and characterized by a fluidal microstructure. If the matrix is completely glassy, a differentiation is made between obsidian and vesicularporous pumice stone. Rhyolite is the volcanic equivalent of granite and forms typically during post-orogenic rifting.
Dense to fine-grained, grey to reddish-brown rock with plagioclase, hornblende, biotite and pyroxenes. Often with additional quartz, calcite, hematite and magnetite. The matrix is often glassy and porphyritic. Andesite is a volcanic equivalent of diorite. It forms especially in the area of subduction zones, island arcs and mid-ocean ridges. It is the typical orogenic rock. The name comes from a 7.500 km long mountain chain, the South American Andes.
Melanocratic dense to medium-grained, occasionally porphyritic rock with a dark grey to black colour. Depending on the chemical composition, a basic differentiation is made between high-alkaline-earth tholeiite basalts (plagioclase basalts) and high-alkali basalts (olivine basalts). Main components in both cases are plagioclase and pyroxene / augite. Olivine, ilmenite, magnetite and titanomagnetite as well as hornblende are present. Basalt is the volcanic equivalent of gabbro. Basalt forms by melting of the earth’s mantle preferably at mid-ocean ridges. In rare cases it can form during plate tectonic rifting at continental tectonic trenches like the Leinetal Trench or the Hessian Sink.
Tholeiite basalt that has been secondarily and extensively transformed by metamorphosis is traditionally referred to as diabase, paleobasalt or greenstone. This is a predominantly dark green, dense to medium-grained, sometimes even porphyric rock. Owing to predominantly weathering-related mineral transformations, plagioclase has more or less transformed into albite and calcite with a calcite content of up to 20 MA %. Clinopyroxene has partly or completely
transformed into amphibole or chlorite. Chlorite contents can be up to 50 MA %.
Under the influence of water fine dusty to sandy ashes solidify into tuff. Per definition tuff consists of > 75 MA % pyroclastic material of all grain sizes. Lithic tuff consists mainly of rock fragments, crystal tuff consists mainly of single crystals. Vitric tuff consists mainly of pumice and glass fragments. Strongly frothy, vesicular, extremely porous and glassy solidified lava is called pumice. Usually the formation of highly porous volcanic ejecta correlate with rhyolitic magma.
are products of rock metamorphosis, which takes place always in deeper layers of the earth, always under increased pressure and/or at increased temperature. Metamorphosis is defined as a mineralogical and structural transformation of rocks while the solid state is maintained. Metamorphic rock can form from igneous rocks or sedimentary rocks. Characteristic is an orientation of minerals, which is often visually detectable as a schistosity or banded structure of the rocks. A special type of rock transformation is the high temperature low pressure metamorphosis by contact with magmatic melts and hydrothermal solutions (contact metamorphosis).
Usually grey to dark-grey rocks with fine to medium-grained structure. Amphibolites form mainly from basalts, andesites and gabbros. Main minerals are amphibole / hornblende, mica and feldspar / plagioclase. The genesis takes place under high pressure and temperature conditions during the orogenesis in subduction zones. Amphibolites occur mostly as inclusions in gneiss and mica slates.
Medium- to coarse-grained, granular-flaser-like or layered, rarely columnar rock consisting mainly of light-coloured constituents. The main minerals are feldspars, accounting for more than 20%, and free quartz as well as 10 to 50% phyllosilicates, especially the micas muscovite and biotite. Gneisses can be formed from igneous or sedimentary starting products. On account of partial melting at high temperatures, fluid transitions to granite-like rocks can occur.
Thinly foliated leafy rock with layered silicates which form a continuous silky coating in the foliation plane. Main minerals are fine scaly light mica / sericite and chlorite as well as quartz. Feldspar and biotite can also occur. Phyllite forms through the metamorphosis of claystone, slate clay and shale.
Usually white-grey to white fine to middle-grained rocks formed by transformation of sandstone during regional metamorphism. Quartzite is mainly made of pure quartz. Quartzite shows characteristic grain bonds of the quartz grains. In rock fillers large amounts of phyllosilicates can be present. They are mostly muscovite, sericite and kaolinite.
are formed by weathering, transport, erosion and deposition followed by diagenetic solidification. Sediments are typical products of the exogenic rock cycle. A differentiation is made between clastic, chemical and biogenic sediments depending on the type of deposition. The following sedimentary rock fillers are of interest for the brick and tile industry:
grey to greenish-grey sometimes also red clastic sedimentary rocks with a considerable content of quartz, feldspar and rock fragments. Chlorite, mica and carbonates as well as clay substance are present as constituent minerals. Greywackes are sometimes referred as impure or poorly separated sandstones. They represent typical flysch sediments and form during orogenesis from submarine turbidity currents / turbidites.
Limestone consists mainly of chemically precipitated calcite in the form of shells and skeleton residues from marine organisms like corals. It also forms from fine-grained clastic sediments made of broken lime reef complexes. Often calcite is in solution before it precipitates. Admixtures of clay are very common in limestone and mark the transition between marl limestones, marlstones and clastic clay marlstones. To use limestone as a rock filler it has to be guaranteed, that the oversize grain fraction is small and that the filler does not suffer from chipping due to lime.
