Critical minerals (Part 11): Manganese – a metal with a long memory): From cave art to critical mineral
Michael C Mackiewicz (USA)
Manganese (Mn) is one of the most widely used metals in modern civilisation, but despite this, Mn has for decades received only passing attention, often overshadowed by headline elements such as lithium, cobalt, nickel and the rare earths. As the twelfth most abundant element in Earth’s crust, manganese is treated as a bulk industrial input, not a strategic resource. It strengthens steel, used in colouring glass, and is a key component in powered dry-cell batteries, but rarely does its importance appear in policy debates or critical-mineral lists.
Despite this apparent abundance and ubiquity, manganese is increasingly described as a “forgotten” critical mineral in the energy transition. This label reflects several underlying realities.
- It plays an essential role in batteries, steelmaking and low-carbon technologies, yet has historically been overshadowed by higher-profile materials.
- It was largely absent from early critical-mineral frameworks, despite its central role in modern industry.
- Potential supply-chain vulnerabilities were underestimated until relatively recently.
- Policy, research and investment have lagged behind its true strategic importance.
Regardless of the “forgotten critical mineral” label, manganese is one of the most widely used alloying elements in steel, essential for nickel, cobalt, manganese (NMC) and lithium iron phosphate (LMFP) battery chemistries, increasingly exposed to geopolitical and supply-chain risk.
Therefore, “forgotten” doesn’t mean unimportant – it means important but benignly neglected.
This shift from neglect to one of recognition reveals how policymakers, industry and researchers now view manganese. As a critical mineral, manganese is not merely an industrial additive, but a strategic component of modern technology.
Today’s classification
Manganese may still be widely described as a “forgotten critical mineral”, but awareness of its importance has changed. Today, manganese is officially recognised as a critical mineral by the USGS, the European Union and the UK. Its importance spans steelmaking, battery technologies, clean-energy infrastructure and advanced alloys.
Manganese: a brief historical and cultural journey
Manganese has been part of the human story far longer than most metals. Long before it became essential to steelmaking or battery chemistry, people used manganese minerals for colour, art and craft. Early humans ground pyrolusite, a black or bluish-black manganese dioxide (MnO2) mineral, with animal fat to create black figures and scenes on the walls of Palaeolithic caves.
The Palaeolithic period (Old Stone Age) ended roughly 10,000 to 12,000 years ago (c. 10,000-8000 BCE) marking the end of the last Ice Age. The fact that these drawings have survived 10,000 to 12,000 years demonstrates manganese’s chemical stability and its role as a molecular time capsule of Palaeolithic creativity.
By the time of the ancient Egyptians and Romans, artisans had discovered that small amounts of manganese could either colour glass purple or remove greenish tints caused by iron impurities, making it a staple of ancient workshops and a key to producing clearer, more vibrant glass. Greek potters refined manganese into the deep blacks seen in ceramics, while Indian metallurgists unknowingly introduced trace manganese into wootz steel, the alloy that would travel the Silk Road and become the legendary Damascus blades. Wootz steel is an ancient South Indian high-carbon steel, famous for its sharpness, toughness, and flowing ‘watered-silk’ (Damascus) patterns.
Magnesia nigra (Latin for “black magnesia”) is the historical term for the mineral pyrolusite (manganese dioxide), from which the element manganese (Mn) was eventually isolated and named. The name ‘manganese’ traces back to ancient descriptions of two stones from the Greek region of the Magnetes, one magnetic (magnetite) and one not (pyrolusite). Over the next couple of centuries, the term evolved from magnesia nigra to manganesa, eventually settling on manganese. Both Mn-bearing materials, mined from the broader region of Magnesia in Greece, were historically confused with iron ores and with magnesia alba (magnesium oxide).
From cave walls to cabinet specimens
Manganese’s story extends beyond metallurgy. It remains culturally, geologically and aesthetically sought after for its mineral forms that range from velvety black oxides to vivid pink carbonates treasured by collectors and museums. Fig. 1 presents generalised depictions of historic uses of manganese: prehistoric cave art, Roman glass and ancient Indian metallurgists forging Wootz steel. Beyond its cultural legacy, manganese’s mineral forms reveal the same diversity that made it valuable to ancient artisans.
Manganese minerals: forms, colours, and why they vary
Manganese minerals are some of the most colourful and varied minerals that collectors are exposed to. Even though pure manganese metal is a silvery-grey element, its minerals can appear as metallic black coatings, soft brown crusts, bright pink crystals, deep red masses, and even rare purple phosphates. These different colours and shapes form because manganese can exist in several chemical states, and each one builds a different kind of mineral structure.
Whether observed in the field or in a collection, manganese most often appears in two main forms. One form is the black manganese oxides, which create dark, metallic or velvety coatings, such as pyrolusite (Fig. 2), psilomelane, and manganite (Fig. 3). The second form is the pink manganese carbonates, such as rhodochrosite (Fig. 4) and kutnohorite, which grow as bright, translucent crystals.
This contrast between stark black and vivid pink is one of the reasons manganese minerals are so prized in museum displays and private collections.
Crystal forms, habits, and variety of colours
Manganese minerals display a wide range of crystal habits (Table 1). A crystal habit is the typical shape or growth pattern that a mineral tends to form again and again. These recurring shapes are the result of the mineral’s internal atomic structure; however, they are also shaped by the conditions in which the crystals grow, such as, temperature, pressure, and space to develop. The result is a distinctive geometry that often becomes a visual hallmark of the species, recognisable in specimens from mines and localities around the world.
| Mineral/group | Typical habit | Description | Growth influences |
|---|---|---|---|
| Pyrolusite | Fibrous sprays | Slender, radiating metallic needles forming fan‑like clusters; classic oxide habit. | Rapid oxidation and limited space promote fibrous growth. |
| Psilomelane group | Botryoidal masses | Smooth, rounded black surfaces with metallic to matte sheen; often massive. | Precipitation from colloidal Mn‑oxide gels in open cavities. |
| Manganite | Acicular prisms | Sharp, elongated black crystals with bright metallic lustre; often parallel bundles. | Stable growth under moderate temperature and pressure. |
| Rhodochrosite | Rhombic/scalenohedral | Pink rhombs or “dog‑tooth” crystals; translucent to gemmy. | Carbonate crystallisation in open fractures with slow cooling. |
| Hollandite | Acicular fibres | Slender, needle‑like black crystals; commonly radiating or tufted. | Mn⁴⁺ framework structure favours linear chain growth. |
| Manganese dendrites | Dendritic coatings | Thin, branching “fern‑like” oxide films on limestone or shale. | Rapid surface oxidation and diffusion along fractures. |
Examples where crystal habits reflect a mineral’s internal structure and chemistry include manganite, whose elongated prisms develop from the stacking of MnO(OH) octahedra and rhodochrosite, whose rhombohedral crystals express the symmetry of the carbonate lattice. The colour variations in manganese minerals are controlled by oxidation state and crystal chemistry:
- Mn²⁺ → pinks and reds. Seen in rhodochrosite and other carbonates.
- Mn³⁺ → brownish-black hues. Common in manganite, braunite and some silicates.
- Mn⁴⁺ → deep blacks and metallic greys. Characteristic of pyrolusite and cryptomelane-rich oxides.
Environmental conditions that determine which oxidation state dominates include pH, oxygen availability and microbial activity. In soils and sediments, manganese cycles between Mn²⁺ and Mn(III/IV) oxides as redox conditions shift.
A shift in soil redox conditions simply means the soil is switching between oxygen-rich and oxygen-poor states. Redox is short for “reduction–oxidation”, but in simple terms it describes how much oxygen is available for chemical reactions. When oxygen is present, the soil behaves one way; when oxygen runs low, it behaves differently. This change affects how nutrients move, how microbes break down organic matter, and how easily plants can take up what they need.
Waterlogging, drying, or a sudden surge of organic material can all push the soil from an aerobic (oxygen present) state to an anaerobic (oxygen limited) one. The same chemistry that drives these soil changes also explains why some minerals shift colour depending on whether they formed in oxygen‑rich or oxygen-poor environments.
Dendrites: nature’s ink drawings
Few manganese features are as iconic as dendrites (Fig. 5), the delicate, branching oxide patterns found on limestone, shale, and sandstone. These are not fossils, but thin films of Mn oxides that precipitated along microfractures when Mn²⁺‑rich fluids oxidised upon exposure to air.
Their fern‑like geometry makes them highly collectible, especially from classic localities such as Solnhofen, Germany and the Welsh slate quarries.
Geological occurrence and deposit types
Manganese minerals occur in a wide range of geological settings, with each environment producing its own distinctive suite of specimens. Table 2 highlights manganese deposit types, from supergene weathering zones and hydrothermal veins, to deep-sea nodules and metamorphic terrains, showing how different geological processes shape the minerals collectors prize. These same deposits also supply industry with manganese for batteries, pigments, catalysts, cosmetics and high-tech alloys. For mineral enthusiasts, the appeal lies in seeing how the beauty of a Mn-bearing mineral specimen tells a story of how Earth processes, alters and redistributes manganese through time.
| Deposit type/ environment | Representative minerals | Features | Industrial significance | Formation process |
|---|---|---|---|---|
| Supergene residual zones | Pyrolusite, wad, psilomelane | Soft black oxides with metallic sheen; botryoidal or earthy textures. | Major source of Mn ore for steel and alloys. | Weathering of Mn‑bearing rocks under tropical oxidation. |
| Hydrothermal veins | Rhodochrosite, manganite, hausmannite | Colourful vein fillings; pink carbonates and lustrous black crystals. | Supplies Mn for catalysts, pigments, and specialty alloys. | Precipitation from hot, Mn-rich fluids in fractures. |
| Sedimentary/marine beds | Cryptomelane, birnessite, pyrolusite | Laminated oxide layers; fine-grained, banded textures. | Important for bulk Mn production and metallurgical feedstock. | Slow chemical deposition from seawater or lake brines. |
| Deep-sea nodules and rusts | Todorokite, vernadite, birnessite | Rounded nodules with concentric layers; dark metallic lustre. | Potential future source for battery‑grade Mn and Co. | Gradual accretion of Mn oxides around nuclei on ocean floor. |
| Metamorphic terrains | Spessartine, rhodochrosite, tephroite | Granular pink and orange silicates in marble or skarn. | Minor Mn source; valued for gem and collector specimens. | Recrystallisation of Mn carbonates under heat and pressure. |
| Volcanic/magmatic settings | Bustamite, rhodonite, braunite | Massive pink silicates and granular oxides; aesthetic specimens. | Trace Mn in magmatic systems; minor industrial role. | Mn substitutes for Fe and Mg during magmatic crystallization. |
Note: Supergene processes and residual zones form near Earth’s surface, where rocks are exposed to air, rainwater and slow chemical weathering. As minerals break down, manganese can be dissolved, moved, re-precipitated, often forming mineable deposits. These zones develop under everyday surface conditions, cool temperatures, normal pressures and circulating rainwater, creating black oxides and botryoidal specimens collectors know well.
Cryptomelane from North Wales
Cryptomelane from North Wales (Fig. 6) is a good example of how a once-overlooked mineral can reveal a richer geological story. It typically forms hard, grey-black, rounded or lumpy “botryoidal” (Fig. 7) masses that may look dull at first glance but show a subtle metallic sheen when freshly broken.
For decades, material like this was simply labelled psilomelane, a catch‑all name used for several manganese oxides. However, recent collecting and analytical work reveals that cryptomelane is more widespread in Wales than early surveys suggested, especially in the Arenig District of Merionethshire. These specimens often occur in near-surface weathering zones, where oxygen and rainwater have altered manganese-rich rocks into soft to moderately hard black oxides. Their botryoidal forms, layered textures, and history of misidentification make Welsh cryptomelane a prized specimen for collectors and is a great reminder that even familiar localities can still hold surprises.
Global production, processing, and industrial demand
From museum specimens to industrial feedstock, manganese’s journey spans both art and industry, connecting the collector’s cabinet to the global supply chain. On the world stage, manganese is a strategic industrial metal, mined in only a handful of countries, even though it is used everywhere steel is made, batteries are built, and chemical processes need a reliable oxidiser. The geography of manganese production and reserves is surprisingly concentrated, with only a few nations dominating mining (Fig. 8), while a different set of countries dominates processing the commodity (Fig. 9).
Locations where manganese mining occurs represent different geological histories, ancient marine basins in South Africa and Gabon, weathered laterites in Ghana and India, and hydrothermal-influenced deposits in Australia and Brazil. But the story doesn’t end at the mine.
Separation between mining countries and processing countries is a critical risk component of the manganese supply chain. Much of the world’s manganese ore is transported thousands of miles before it becomes something useful. China, for example, processes a large share of the world’s manganese into alloys and battery-grade chemicals, even though its own ore production is modest by comparison.
The uses of manganese are just as geographically widespread. Steelmaking consumes the overwhelming majority, roughly 85-95% of all manganese produced, because the metal removes oxygen and sulphur from molten steel and strengthens the final alloy. The remaining 5-15% of the processed Mn-material goes into batteries, pigments, fertilisers, catalysts and specialty chemicals. As electric-vehicle production expands, high-purity manganese sulphate has become a growth market, feeding the cathodes of NMC and LMFP battery chemistries.
For a mineral that collectors often encounter as delicate sprays or glossy botryoidal masses, manganese has an outsized industrial footprint. Its mining is concentrated, its processing is global, and its uses ranges nearly every manufactured sector, from rebar and rail steel to alkaline batteries, pigments and even agricultural fertilizers. Understanding where manganese is mined, where it is refined, and where it is consumed helps place each specimen in a broader context: a mineral that is both a geological curiosity and a cornerstone of modern industry.
Summary
Manganese, long hidden in the shadows of lithium, cobalt and nickel, it is now recognised as a critical mineral essential to steelmaking, battery chemistry and clean energy technologies. Its story spans human history, from Palaeolithic cave art and Roman glassmaking, to modern alloys and battery cathodes. The mineral’s diverse forms, colours, and oxidation states reflect its complex geochemical behaviour and aesthetic appeal to collectors. Today, manganese’s concentrated mining and widely dispersed processing centres highlight a supply-chain risk built into the metal’s geography, creating conditions where the separation between production and refinement can lead to global problems.
References
European Commission (2023). Study on the Critical Raw Materials for the EU. Available at: https://single-market-economy.ec.europa.eu
Trufin (2024). Geochemistry resources and mineral photography archive. Available at: https://www.trufin.com
Mindat.org (2024). Manganese minerals and locality database. Hudson Institute of Mineralogy. Available at: https://www.mindat.org
U.S. Geological Survey (2024). Mineral Commodity Summaries: Manganese. Available at: https://pubs.usgs.gov/periodicals/mcs2024/mcs2024-manganese.pdf risk.)
Additional reading
British Geological Survey (BGS). Manganese: Mineral Profile. Available at: https://www.bgs.ac.uk
Geology.com (Hobart King). Manganese: Uses, Facts, and Geology. Available at: https://geology.com
Royal Society of Chemistry (RSC). Periodic Table: Manganese. Available at: https://www.rsc.org/periodic-table/element/25/manganese