Naujaite
Category: Plutonic
Type Alkaline rock.
Commons Naujaite is a local name for the nepheline-sodalite syenite. Naujaite is agpaitic [(Na+K) /Al≥1,2], Si-undersaturated plutonic rock occurring in alkaline layered intrusions.
Name origin The rock is named after the Naujakasik (now Naajakasik) locality in Greenland.
Locality Kangerdluarssuk, the Ilímaussaq magmatic complex, Greenland – the type locality for eudialyte, arfvedsonite, sodalite, aenigmatite, rinkite and other minerals (sample courtesy of M. Marks).
GPS:
Major minerals Sodalite, nepheline, aegirine, arfvedsonite, audialyte, microcline.
Accessory minerals Apatite, rinkite, aenigmatite, hiortdahlite, steenstrupine-(Ce), aphalerite, fluorite.
Classification According to modal composition in the QAPF diagram for plutonic rocks (Streckeisen, 1976), the field of foidic syenite is defined by the modal composition of foids (F 10-60 %) and the plagioclase ratio P/(P+A) from 0 to 10. The rock projects in the lower part of the QAPF diagram. Naujaite contains foids corresponding to nepheline and dominant sodalite. Hence, the rock can be named as nepheline-sodalite syenite.
Colour Light, with pink eudialyte and dark arfvedsonite crystals.
Structure Phaneritic, pegmatitic.
Granularity Medium– to coarse-grained.
Texture Poikilitic.
Alterations Zeolitization of sodalite, nepheline and K-feldspar to secondary analcime and natrolite. Breakdown of primary arfvedsonite to a symplectite composed of biotite and aegirine.
Petrographic characteristics Medium- to coarse-grained naujaite is a member of the upper cumulate layer vertically differentiated to the pulaskite – foyalite – sodalitic foyalite – naujaite succession. Alternatively, it occurs in form of autoliths in kakortokite. The rock is typical of its poikilitic structure with euhedral chadacrysts of sodalite (up to 1 cm in size) enclosed in interstitial oikocrysts of alkali feldspars, aegirine, arfvedsonite and eudialyte (up to 10 cm in size). Sodalite can occupy as much as 50 vol. % of rock.
Usage Potential source of Nb, Ta, Zr, Hf, REE, Y. Limited exploratory exploitation of Zr,REE-rich kakortokite, naujaite and marginal pegmatite occurred in the 1980s of the 20th century in southern Greenland.
Literature Bailey, J.C., Gwozdz, R., Rose-Hansen, J. & Sørensen, H., 2001: Geochemical overview of the Ilímaussaq alkaline complex, South Greenland. Geology of Greenland Survey Bulletin, 190, 35-53. Sørensen, H., 2001: The Ilímaussaq alkaline complex, South Greenland: status of mineralogical research with new results. Geology of Greenland Survey Bulletin, 190, 167 pp.
Photomicrographs
Sodalite chadacryst – Sdl enclosed in alkalic feldspar – Kfs. Alkalic amphibole – arfvedsonite Arf – exhibits a pronounced pleochroism in plan-parallel polarized light and high interference colours in crossed polars (upper images). Euhedral sodalite chadacryst – Sdl enclosed in the eudialyte oikocryst embedded in sodalite and alkali feldspar – Kfs (bottom images). Width of all photomicrographs corresponds to 2.2 mm.
Normative composition
High Na2O content in naujaite is expressed in a very rare normative mineral – sodic metasilicate – ns. The rock is undersaturated in quartz, what is obvious from the presence of normative olivine – ol and nepheline – ne. An increased content of the normative zircon – z is also interesting.
Normative minerals
SiO2
TiO2
ZrO2
Al2O3
Fe2O3
FeO
MnO
MgO
CaO
Na2O
K2O
P2O5
F
S
CO2
Total
Molar proportion of normative mineral
Molecular mass of normative mineral
Weight % of normative mineral
Oxide
(wt. %)
48.25
0.32
0.49
19.30
4.07
3.08
0.21
0.10
1.68
14.37
3.41
0.06
0.08
0.11
95.53
Molecular
weight
60.08
79.88
123.22
159.69
159.69
71.85
70.94
40.31
56.08
61.98
94.20
141.95
32.06
44.01
Molecular
proportion
0.8031
0.0040
0.0040
0.1893
0.0255
0.0458
0.0030
0.0025
0.0300
0.2318
0.0362
0.0004
0.0025
0.0025
ap
0.0014
0.0004
0.0004
328.68
0.14
pr
0.0012
0.0025
0.0012
119.98
0.15
il
0.0040
0.0040
0.0040
151.75
0.61
cc
0.0025
0.0025
0.0025
100.09
0.25
z
0.0040
0.0040
0.0040
183.31
0.73
or
0.2172
0.0362
0.0362
0.0362
556.67
20.15
ab´
0.9185
0.1531
0.1531
0.1531
524.46
80.29
ac
0.1019
0.0255
0.0255
0.0255
462.02
11.78
ns
0.0533
0.0533
0.0533
122.07
6.50
zvyšky
0.0406
0.0025
0.0260
di
0.0521
0.0245
0.0015
0.0260
0.0260
246.28
6.42
hy´
0.0170
0.0160
0.0010
0.0170
130.1126818
2.21
ol
0.0085
0.0160
0.0010
0.0085
200.14
1.70
ne
0.2762
0.1381
0.1381
0.1381
284.11
39.24
ab
0.0899
0.0150
0.0150
0.0150
524.46
7.86
D: 0.5609
D1: 0.5524
D2: 0.5524
Mg/(Mg+Fe2+): 0.058
Total of normative wt. % 95.53
Comment Normative anorthite – an was not created owing to missing aluminium, which had been exhausted for the creation of normative orthoclase – or and albite – ab. All provisional hypersthene – hy´ was affiliated to olivine - ol. A portion of the provisional albite – ab´ was used up in the normative nepheline ne and real albite – ab. An increased S concentration is expressed in the normative pyrite pr . Similarly, the Zr content is projected in the normative zircon – z.
Chemical composition
Naujaite is peralkaline rock with high Na2O and K2O, and low CaO and MgO contents. The molar ratio (Na2O + K2O)/Al2O3 is very high – 1.42 (see table with chemical composition). The term agpaitic is used mainly for nepheline syenites with the molar ratio (Na2O + K2O)/Al2O3 greater than unity accompanied by increased Na, F, Cl, Zr, and low Ca and Mg contents. This term is recently reserved for peralkaline nepheline syenites containing complex Zr- and Ti-bearing minerals, such as eudialyte. The term agpaitic must not be interchanged with the term peralkalic, which expresses only the molar ratio of alkalis and aliminium. Compared to Si-saturated syenites (q in the norm), naujaite is characteristic of increased Na2O, Al2O3 and SiO2 contents. Increased ZrO2, LREE, Hf, Y and Zn contents are also diagnostic. In addition, naujaite also has an increased Cl content (up to 2.5 wt. %).
-
SiO2
48.25TiO2
0.32Al2O3
19.30Fe2O3
4.07FeO
3.08MnO
0.21MgO
0.10CaO
1.68Na2O
14.37K2O
3.41P2O5
0.06H2O+
1.25H2O-
0.17CO2
0.11SO3
0.20F
0.16Cl
2.34Total
99.57Mg(Mg/Fe2+)
0.05A/CNK
0.64A/NK
0.71