Classification and Description
Represented by the chemical formula MnO2, manganese dioxide is an inorganic compound. Usually appearing brown or blackish, it is a solid mineral that exists naturally as an ore of Manganese in the form of ‘pyrolusite’ is an ore which bears multiple oxides of manganese with the chemical formulae MnO, MnO2 and Mn3O4.
When used as a pigment in the production of bricks, it also exists as the synthetic compound of hausmannite, MnO (manganosite) and Mn2O3 (manganese trioxide). MnO2 and Mn3O4 bricks are produced in large volumes globally via the use of the manganese as a brown clay pigment
Derived from the refining of ferromanganese, Mn3O4 is also mined and exists naturally as umbers or braunite and is used in several applications including the production of dense and strong brown bricks, owing to the addition of a brown clay pigment. Likewise, it can also be employed in the production of dark brown bricks with a combination of clay. Clay can be unstable when fired at extremely high temperatures and in some instances requires a stronger variant of manganese to produce a darker shade of brown - or even black.
Manganese dioxides and oxide powder are also used in the production of dark shades of red fired clay and in the production of dark brown facing bricks, ceramic bricks, pavers and roof tiles.
Broadly speaking, therefore, the various oxides of manganese occur in ores together - and are thus mined together. Manganese umber is a mixture of all of these and the iron oxide that is commonly found alongside the manganese in the rock. In some cases, pretreatment of the umber prior to using it as a ceramic pigment is possible via calcination. If this occurs, an even darker pigmentation to the final product is possible.
Manganese umber as supplied by African Pegmatite has the following specification.
| Appearance | Dark brown powder |
| Manganese:iron ratio | 4.8:1 |
| Manganese content (by weight) | 43 - 47% 42% is available on request |
| Other notable compounds present | SiO2 4 - 6%; CaO 5 - 7% |
| Particle size | 45 μm typical |
| Bulk density (tapped) | 1.53 - 1.55 g cm-3 |
Bulk stability is good for manganese umber - being shelf stable for lengthy periods of time. Particle size can be tuned to a particular specification, mixability and thorough dispersal is good. When included in a clay mixture for the production of bricks or ceramics, the firing stability is good. Firing temperatures in the standard range (up to ca. 1,300 °C) are well tolerated, although slightly lower temperatures (ca. 1,150 °C) are preferred with the added benefit of requiring less manganese umber to achieve the same colour. With the bulk density value, there is no significant weight penalty to using manganese umber.
As a general rule of thumb, manganese oxide pigments for bricks, tiles and ceramics are preferred as a little pigment goes a long way. In most cases, as little as 1 to 6% by weight of the pigment needs to be used - meaning manganese umber is very cost effective, even on the largest of scales. Naturally, the impact of the identity of the clay itself will play a major role, especially with regard to firing temperature. Manganese umber incorporation into a clay ceramic needs a minimum of 850 °C.
Benefits of Manganese Oxide
Manganese has two major advantages that both help to improve the use and structure of bricks.
- As opposed to regular red bricks, MnO2 bricks and Mn3O4 bricks absorb less water
- The inclusion of the manganese oxides greatly improves the surface structure of bricks, making it a more smooth and homogenous choice.
The combined result is that a smoother, more refined and uniform brick structure is produced that is more visually appealing.
Braunite Explained
Braunite is an ore of manganese that falls into a group referred to as ‘compound oxides’. Braunite is represented by the chemical formula Mn2+Mn3+6[O8|SiO4], meaning it interestingly contains manganese in two oxidation states. Braunite will often crystallise and form small crystals of dipyramidal habit when placed in a tetragonal system.
Braunite often spots a pure black, matte black lustre or semi-metallic black colour. Additionally, it can be said to exhibit partial magnetism properties and ranks 4 on the denseness hardness scale.
Braunite is commonly used in the production of pavers, bricks and roof tiles – in these applications braunite is known to produce natural brown hues that shine on the surface of the clay.
Product Advancements
Because we are pioneers and pacesetters at African Pegmatite, we continuously invest and seek new ways to improve both our production style and methods, in a bid to consistently offer innovative and exciting products to our clients. Recently, we developments include a grey firing oxide, black brick oxide and the exclusive ‘true red’ brick manganese – this isn’t the regular Terracotta or usual orange you are familiar with, but rather a brick with amazing and striking red details. Contact us to learn more about our newest product.
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