Nb – Niobium Introduction

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Nb – Niobium 

 

Introduction 

 

Niobium, also known as columbium (Cb) in 

the USA, belongs to group 5 of the periodic table, 

along with V and Ta.  It has an atomic number of 

41, an atomic mass of 93, two oxidation states (+3 

and +5) and one stable isotope (

93

Nb).  Although 

it is metallic in many respects, its chemistry in the 

+5 oxidation state is more typical of non-metals, 

as it forms numerous anionic species and very few 

cationic compounds.   

Niobium is a lithophile metallic element.  Nb

5+

 

has an ionic radius of 64 pm, which is identical to 

that of Ta

5+

, so these elements are usually found 

together in minerals.  Niobium forms several 

rather rare, but economically important minerals, 

including pyrochlore (Na,Ca)

2

(Nb,Ta)

2

O

6

(OH,F), 

columbite-tantalite (Fe,Mn)(Nb,Ta)

2

O

6

 and 

stibiocolumbite Sb(Nb,Ta)O

4

.  It is more widely 

present at trace levels in rock-forming minerals 

such as biotite, rutile, sphene, cassiterite and 

zircon; of special geochemical significance is the 

ionic substitution of Nb for Zr in zircon, since this 

mineral is widely distributed in igneous rocks.  

Pollard (1989) reports that Ta and Nb 

mineralisation is often associated with alkali 

granite, characterised by high fluorine levels, and 

by the development of pervasive, post-magmatic 

alteration.  Niobium also occurs in bauxite.  

High Nb concentrations are found in late stage 

magmatic differentiates, and felsic igneous rocks 

generally have the highest contents.  Shale and 

granite tend to have the highest Nb 

concentrations, and limestone and sandstone the 

lowest.  Nb

5+

 also substitutes for Ti

4+

 in its 

compounds, and is thus found in above normal 

concentrations in areas with mafic rocks 

(Reimann et al. 2003).  The crustal abundance of 

Nb is estimated to be 20 mg kg

-1

 (Wedepohl 1978, 

Fyfe 1999), based on averages for granitic rocks, 

granodiorite and diorite with 22 mg kg

-1

; gabbro 

and basalt 10 mg kg

-1

; syenite and alkalic rocks 

100 mg kg

-1

, and peridotite 1.5 mg kg

-1

.  

Therefore, alkaline rock complexes, e.g., syenite, 

nepheline syenite, alkali granite and alkaline 

ultramafics, have the highest Nb content of all 

magmatic rocks (Neiva 1999).  Data on the Nb 

content of sedimentary rocks are scarce, although 

there are sufficient analyses for Wedepohl (1978) 

to quote a value of 17 mg kg

-1

 Nb for argillaceous 

rocks.  Willis and Ahrens (1962) and Willis 

(1970) present data for Mn nodules from different 

oceans, giving average values in the range 32–41 

mg kg

-1

 Nb.  The average value for loess is given 

as 20 mg kg

-1

 (McLennan and Murray 1999).  

Data on metamorphic rocks is similarly scarce; an 

average of 26 mg kg

-1

 is given by Wedepohl 

(1978) for quartzofeldspathic rocks from the 

Canadian shield. 

Niobium displays very low mobility under all, 

but the most extreme environmental conditions, 

due to the high stability and very low solubility of 

the oxide Nb

2

O

5

 and niobates derived from this 

(Brookins 1988).  However, the presence of citric, 

tartaric and oxalic acids increase the solubility of 

Nb through chelation.  The maximum 

concentration of Nb in stream water, based on 

solubility  calculations,  is  likely to be about 10 

µg l

-1

 (Office of Civilian Radioactive Waste 

Management website).  In sea water and most 

other surface water, Nb concentrations are likely 

to be much lower (Sohrin et al. 1998).    

Anthropogenic sources of niobium include 

nuclear fuel production, welding and steel 

production (Reimann and de Caritat 1998).  It is 

also used in the manufacture of missiles, cutting 

tools, pipelines and super magnets.   

Niobium is considered non-essential, but it is 

present in living organisms and can affect 

biological mechanisms.  Little is known about its 

toxicity. 

Table 48 compares the median concentrations 

of Nb in the FOREGS samples and in some 

reference datasets. 

 

 

Nb in soil 

 

The median Nb content is 9.76 mg kg

-1

 in 

subsoil and 9.68 mg kg

-1

 in topsoil;  the range is 

from 0.24 to 133 mg kg

-1

 in subsoil and from 0.45 

to 134 mg kg

-1

 in topsoil.  The average ratio 

topsoil/subsoil is 1.008. 

Low  Nb  values in subsoil (<6.0 mg kg

-1

) 

occur in  central  Finland,  in  western  Ireland,  in  

the glacial   drift   area   from  the  Netherlands  to  

 

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Table 48. Median concentrations of Nb in the FOREGS samples and in some reference data sets.

 

Niobium 

(Nb) 

Origin – Source 

Number of  

samples 

Size fraction 

mm 

Extraction 

Median 

mg kg

-1

Crust

1)

Upper continental 

n.a. 

n.a. 

Total 

12 

Subsoil 

FOREGS 

790 

<2.0 

Total (ICP-MS) 

9.76 

Topsoil 

FOREGS 

843 

<2.0 

Total (ICP-MS) 

9.68 

Soil

2)

World n.a. 

n.a.  Total  12 

Water 

FOREGS 

807 

Filtered <0.45 

µm 

 

0.004 (µg l

-1

) 

Water

3)

World 

n.a. 

n.a. 

 

0.001 (µg l

-1

) 

Stream sediment 

FOREGS 

852 

<0.15 

Total (XRF) 

13.0 

Floodplain sediment 

FOREGS 

749 

<2.0 

Total (XRF) 

10.0 

1)

Rudnick & Gao 2004, 

2)

Koljonen 1992, 

3)

Ivanov 1996.

 

Lithuania, in calcareous areas of southern and 

eastern Spain, and in small alluvial areas in 

coastal Portugal, the Paris basin and central 

Hungary.   

In  subsoil,  Nb  shows  high   values   (>13  

mg kg

-1

) in the Massif Central in France, in 

northern Portugal and Galicia in north-west Spain, 

and reflects the major leucogranitic bodies and 

related greisen cupola mineralisation (enriched in 

Be, Li, Nb, W, Sn, Ta, etc.). In Galicia it has been 

shown that Nb anomalies are related to 

episyenites developed in shear bands within 

granitic rocks. High values also occur in  central 

Germany, in the alkaline magmatic province of 

Italy, and in a large area including north-eastern 

Italy, Slovenia, Croatia and adjacent areas of 

Austria and Hungary.  It is also high in northern 

Sweden, and a few isolated points in southern 

Norway, near Rovaniemi (Finland), Mourne 

granite (northern Ireland), and Glasgow 

(Scotland).  High Nb values in Greece are found 

in terra rossa soil (Epirus, Kefallinia), felsic rocks 

(central Macedonia) and near to bauxite and 

phosphorite mineralisation (central and western 

Greece). 

There is little difference between the topsoil 

and subsoil Nb distribution maps.  However, the 

Pyrenees show a continuous Nb anomaly in 

topsoil, and in southern Italy, Nb anomalies are 

stronger, related to peralkaline volcanics. 

Niobium and Ta are closely associated in 

phyllosilicate and oxide minerals, such as 

columbo-tantalite and pyrochlore, but they are 

also present as traces in other oxides.  As 

expected, their correlation is very strong:  0.85 in 

subsoil, and 0.83 in topsoil.  Anomalies of Ta-Nb 

can be subdivided into those related to primary 

crystalline massifs (see Be), and those related to 

alluvial deposits (see Zr). 

In subsoil, Nb also shows a strong correlation 

(>0.6) with Th, Y, the REEs, Al, Ga, In, Ti and 

Rb, and a good correlation (>0.4) with Be, U, Fe, 

V, Sc, Mn, Co, Zr, Hf, K, Ba, Cs, Tl, Pb, Ag and 

Zn.  Correlations are very similar in topsoil. 

 

 

Nb in stream water 

 

Niobium values in stream water range over 

only two orders of magnitude,

 

from <0.002 

µg l

-1

 

to 0.096 

µg l

-1

 (excluding an outlier of 0.34 

µg l

-1

), 

with a median value of 0.004 

µg l

-1

.  Analysis is 

not adequate, since about 25% values are below 

the analytical quantification limit.   

Lowest  Nb  values  in stream water (<0.002 

µg l

-1

) in stream water are predominantly found in 

most of Spain and northern Portugal, in western, 

southern and north-eastern France and southern 

Sardinia (Variscan and Alpine Orogen terrains), in 

all Switzerland and most of Austria and Slovenia, 

western Croatia, in all northern Italy, most of 

Greece, eastern Hungary and southern Poland, all 

characterised by Alpine Orogen terrains.  The low 

values in south-western and northern Norway, 

throughout northern Sweden and Finland, are 

 

262

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characterised by Caledonides and Precambrian 

terrains, and in western Scotland and central 

England in the Caledonides, may show a dilution 

effect by heavy rainfall.  There appears to be no 

reliable correlation with the geology at these low 

(near-detection) levels. 

Highest Nb concentrations in stream water 

(>0.03 

µg l

-1

) are found in the glacial drift of 

Denmark, southern Sweden and Finland, 

characterised by Precambrian terrains, and in 

central and southern Italy, controlled by recent 

alkaline volcanism and related hydrothermalism 

of the Roman Neapolitan and Vulture 

geochemical provinces.  Enhanced Nb values 

(>0.015 

µg l

-1

) also occur in southern Sweden and 

Finland and northern Poland (Precambrian 

terrains), and over the Massif Central of France 

(Variscan terrains).  In northern Poland, as well as 

in the Baltic Countries and southern 

Fennoscandia, high concentrations are correlated 

with DOC, which shows a regional relationship 

with peat land, and is responsible for increasing 

the mobility of certain ions in a humid climate and 

alkaline conditions; the geochemical mobility of 

Nb is thus similar to that of Ba, Mo, Ni, Sr, Zn 

and even Zr (Kabata-Pendias2001, Perel’man 

1977, 1989, Ivanov 1996).    Complexation by 

chelation with organic acids in peaty waters may 

be responsible for the mobilisation of small 

amounts of Nb in these areas. The Nb anomalies 

in northwestern Germany, like those of Zr, Ti, Al, 

V and the REE, correlate with high DOC values. 

They are mainly related to environmental 

conditions. Highly anomalous values in eastern 

France  are in streams affected by salt 

exploitation. 

The Nb distribution pattern in stream water 

follows generally the REEs  patterns model that is 

chiefly climate dominated, but also the “Alkaline 

rocks elements”, and the inverse “Major- ions” 

pattern.  Stream water high in Nb is acidic, of low 

mineralisation and high soluble organic matter, 

and the major soluble species are organic 

complexes.  The rare high Nb areas in soil and/or 

sediment with a high Nb signature in 

corresponding stream water occurs only in the 

south of Sweden and Finland, in the Central 

Massif in France, and in alkaline volcanic areas of 

Italy; in the latter two cases, they are related to 

alkaline magmatism.  

 

 

Nb in stream sediment 

 

The median Nb content in stream sediment is 

13 mg kg

-1

,  and  the  range  is  from  <1 to 281 

mg kg

-1

. 

The Nb distribution map shows low stream 

sediment values (<10 mg kg

-1

) mainly in eastern 

Finland, central Sweden, the glacial drift covered 

northern European plain from Poland to the 

Netherlands, the Baltic states, central Ireland, the 

Jura and south-eastern France, most of Greece, 

northern and central Italy, north-easternmost Italy 

and adjacent part of Austria, Dalmatian Croatia, 

southern and eastern Spain. 

High  Nb  values  in  stream  sediment (>16 

mg kg

-1

) are found mainly in the French Massif 

Central (often associated with Be-Sn enriched 

granite), the north-west Iberian Peninsula (granitic 

and metamorphic rocks of the Iberian Massif), the 

Canary Islands, the Roman Alkaline Province, 

Corsica, an area from south-east Austria to 

Pannonian Croatia and western Hungary, western 

Bohemia and adjacent areas of Germany, 

Scotland, Cornwall, southern and central Norway, 

the granitic Kiruna area of northern Sweden and 

south-western coastal Sweden.  Point anomalies 

are found in Estonia (phosphorite mineralisation), 

northern Ireland (Mourne granite), northern 

Germany, northern Hungary, in Campania 

(volcanics), near Verona in Italy, and in western 

Crete over Neogene sediments with Fe 

mineralisation.   

Niobium in stream sediment shows a strong 

correlation with Ti (0.77), Ta (0.72), and with 

some heavy REEs (Dy, Ho, Er, Tm, Yb). It has a 

good correlation (>0.4) with Th, U, Zr, Rb, Al, 

Ga, Fe, V, Y and all the remaining REEs.  

Niobium has a good negative correlation with 

CaO (-0.41).  Concentration of heavy minerals in 

detrital sediments is probably responsible for 

some point anomalies in which Nb-Ta 

(columbite), Zr (zircon), REEs (monazite) and Ti 

(rutile) are associated. 

   

 

 

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Nb in floodplain sediment 

 

Niobium values in floodplain sediment vary 

from  <1  to  125  mg kg

-1

, with a median of 10 

mg kg

-1

.   

A notable feature of the Nb distribution in 

floodplain  sediment  are  the  low  values   (<7 

mg kg

-1

) over the glacial drift covered plain 

extending from north Germany and Poland to the 

Baltic countries.  Other areas with low Nb values 

are the metamorphic basement rocks of northern 

Norway and eastern Finland; most of calcareous 

Ireland and carbonate rocks of north-east England, 

the karst Dalmatian coast of Croatia, parts of 

Albania and Greece with ophiolite, limestone and 

flysch; the carbonate and clastic rocks of the 

Meseta Central and eastern Spain, the alluvial 

plains of the lower Garonne and the Rhône river 

basins in France; the molasse basin of southern 

Germany and central Austria. 

High Nb values in floodplain sediment (>13 

mg kg

-1

) occur in south-west Finland (crystalline 

rocks), southern, eastern, central-eastern and 

northern Sweden (felsic crystalline rocks), 

northern-central-southern Norway, western 

Scotland, Wales (felsic volcanics), in south-east 

England, Cornwall (granitic area with an 

anomalous value of 42 mg kg

-1

), the southern 

Armorican Massif with felsic rocks in France, a 

small area in north-east France and adjacent 

Belgium with sediments rich in heavy minerals, 

and the Massif Central (associated with Be-Sn 

enriched granite).  Further, high Nb values occur 

over central and northern Portugal and adjacent 

western Spain (granitic and metamorphic rocks of 

the Iberian Massif), the Harz Mountains, 

Erzgebirge (with two anomalous values of 43 and 

29 mg kg

-1

) and Bohemian Massif, which are all 

apparently associated with granitic intrusions and 

mineralisation.  Similarly, the large area with high 

Nb values extending from the Austrian-Italian 

Alps, into Slovenia, Croatia, Hungary to south-

west Slovakia and the Moravian Heights in the 

Czech Republic; in this area there is a striking 

similarity with the Ti pattern, suggesting that the 

origin is not related to granite.   

In the karstic soil of Slovenia and Croatia, the 

high Nb values in floodplain sediment may be 

explained by their association with TiO

2

, which 

tends to be concentrated in the residual soil, and 

its subsequent erosion and deposition on the 

floodplains.  High Nb values are also found in the 

central Swiss-Italian Alps (felsic intrusives and 

mineralisation), the Roman Alkaline Province, 

and  Corsica  (felsic intrusives and 

mineralisation). 

The Nb point floodplain sediment anomaly in 

northern Italy is associated with the Colli Euganei 

alkaline volcanic rocks.  The high value in 

western Crete is over Mesozoic and Neogene 

sediments (phyllite, limestone) with nearby Fe 

mineralisation (limonite, haematite, pyrolusite, 

alunite).  An outlier of 125 mg kg

-1

 Nb occurs on 

Gran Canaria in the Canary Islands (draining 

basaltic and trachytic alkaline volcanic rocks, rich 

in Nb). 

Niobium in floodplain sediment has a very 

strong correlation with Ti

2

O (0.86), a strong 

correlation (>0.6) with Ta, Al

2

O

3

, Ga, Fe, V, Rb, 

Th, Y and most REE, and a good correlation 

(>0.4) with K

2

O, Co, Li, Be, U, Tl, Zr and the 

remaining REEs - Ho, Tm, Yb and Lu. 

It is concluded that the Nb spatial distribution 

in floodplain sediment is related to bedrock 

geology, but also to clay-rich soil with high Al

2

O

3

 

contents.   

 

 

Nb - comparison between sample media 

 

Patterns in Nb distribution between all solid 

sample media are generally similar.  The main 

differences are the higher Nb observed in soil in 

the alkaline volcanic provinces of Italy compared 

to all other solid sample media.  Niobium is also 

lower in stream sediments along coastal Croatia 

and Slovenia (possibly removal of fine-grained 

material from the residual soil).  In floodplain 

sediments throughout south-west Finland, Nb data 

are higher than in all other solid sample media. 

A boxplot comparing Nb variation in subsoil, 

topsoil, stream sediment and floodplain sediment 

is presented in Figure 31. 

Patterns in stream water Nb data are generally 

opposite to distributions observed in solid sample 

media, except in the volcanic provinces of Italy 

(in which Nb is high in all sample media) and in 

Greece (where all data are generally low).  In 

northern Europe, distributions are controlled 

strongly by DOC, since Nb is generally highly 

 

264

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insoluble unless complexed with organic 

substances.  Highest concentrations are, therefore, 

associated with the organic rich environments of 

most of southern and central Fennoscandia, as 

well as throughout Lithuania, Latvia and northern 

Poland.  In southern Europe, low Nb in stream 

water is influenced more by pH, since Nb is 

insoluble under alkaline conditions. 

Figure 31. Boxplot comparison of Nb variation in subsoil, topsoil, stream 

sediment and floodplain sediment.

 

 

 

265