AGPAITE

 

Far-northwestern Russia’s Kola Peninsula is famous for its abundance of unusual rocks & rare minerals.  What makes the Kola’s rocks strange?  This is the location of the Khibina Massif, a large alkaline igneous pluton intruded into Precambrian basement rocks of the Fennoscandian Shield/Baltic Shield.  The intrusion took place during the Caledonian Orogeny - its rocks date to the Late Devonian (~362-365 m.y.).

 


 

First, here’s a pegmatitic agpaite (= pegmatitic peralkaline nepheline syenite) containing purplish-red eudialyte (Na4(Ca,Ce)2(Fe,Mn,Y)ZrSi8O22(OH,Cl)2), black aegirine pyroxene (NaFeSi2O6), and mottled whitish-grayish nepheline (NaAlSiO4) & albite (NaAlSi3O8).

 

Agpaite (pegmatitic peralkaline nepheline syenite) (cut & polished surface; 8.1 cm across) from the Late Devonian Khibina Massif at Nyorkpakhk Mountain (north of the Vuonemmiok River, west-central Kola Peninsula, Murmansk Region, far-northwestern Russia).

Purplish red = eudialyte

Greenish-black = aegirine pyroxene

Mottled grays = nepheline & albite

 


 

The second rock shown below is also an agpaite, but it’s also got a large, radiating cluster of intensely lustrous, golden-brown astrophyllite blades.  Astrophyllite is a rare mineral having the formula (K,Na)3(Fe,Mn)7Ti2(SiO3)8(O,OH)7 - potassium sodium iron manganese titanium hydroxy-oxysilicate.

 

Astrophyllitic agpaite (peralkaline nepheline syenite with astrophyllite) (8.7 cm across at its widest) from the Late Devonian Khibina Massif of Russia’s Kola Peninsula. 

Whitish/grayish = nepheline

Greenish-black = aegirine pyroxene

Dirty red = eudialyte

Golden brown/dark brown = astrophyllite.

 


 

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