AGPAITE
Far-northwestern RussiaŐs Kola Peninsula is famous for
its abundance of unusual rocks & rare minerals. 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
itŐs 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.