Lujavrite Identification Guide
How to identify Lujavrite, a rare agpaitic nepheline syenite, by its dark layered fabric, aegirine, and eudialyte.
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What Lujavrite Looks Like
Lujavrite is a rare, dark, igneous rock — an agpaitic (alkali-rich) variety of nepheline syenite with a strongly aligned, almost layered or trachytoid texture. It is dominated by sodium-rich minerals and is geologically famous from alkaline intrusions.
- Color: dark gray to greenish-black, often with pink, red, or brown speckles
- Luster: dull groundmass with glinting cleavage faces on feldspar and aegirine
- Texture: medium-grained, distinctly foliated/laminated with aligned needle-like crystals
- Key minerals: aegirine (black-green needles), alkali feldspar, nepheline, eudialyte (pink-red), arfvedsonite
Step-by-Step Field ID Checklist
- Note the dark, streaky alignment — parallel orientation of slender dark minerals gives a flow-like fabric.
- Spot pink-to-red grains of eudialyte scattered through the dark groundmass — a hallmark of agpaitic rocks.
- Look for glassy gray nepheline (greasy luster) between the feldspars.
- Check overall darkness — lujavrite is a melanocratic (dark) nepheline syenite.
- Test hardness — feldspar and aegirine are ~5.5-6, scratching glass.
Key Diagnostic Tests
- Mohs hardness: mixed, ~5.5-6 overall (feldspar/pyroxene).
- Texture: trachytoid/laminated alignment is diagnostic versus massive syenite.
- Acid: no significant reaction (silicate rock).
- Density: moderate, similar to other syenites (~2.7-2.9).
- Mineral test: confirm nepheline (gelatinizes with acid in lab) and eudialyte color.
Common Look-Alikes and How to Tell Them Apart
- Ordinary nepheline syenite: lighter and more massive; lujavrite is darker and strongly laminated.
- Kakortokite: a layered agpaitic rock too, but kakortokite shows distinct repeating black-red-white layers; lujavrite is more uniformly dark and streaky.
- Foliated dark gneiss/amphibolite: metamorphic and lacks eudialyte/nepheline; check for the pink eudialyte and feldspathoids.
- Basalt: fine-grained and lacks visible feldspathoids and the laminated coarse fabric.
Where It Is Typically Found
Lujavrite occurs in alkaline igneous complexes. Its type area is the Lovozero massif (Kola Peninsula, Russia), and it is also classic from the Ilímaussaq complex in southern Greenland.
Frequently asked questions
What is Lujavrite?
Lujavrite is a rare, dark, agpaitic (highly alkaline) nepheline syenite with a strongly laminated texture, rich in aegirine, alkali feldspar, nepheline, and eudialyte.
How do you identify Lujavrite?
Look for a dark, streaky, laminated igneous rock with aligned dark needles (aegirine), greasy gray nepheline, and scattered pink-red eudialyte grains — the eudialyte and trachytoid fabric are the best clues.
Lujavrite vs kakortokite?
Both are agpaitic rocks from the same complexes, but kakortokite shows striking repeating black-red-white layers, while lujavrite is more uniformly dark with a streaky, flow-aligned texture.
Where is Lujavrite found?
It is classic from the Lovozero massif in Russia's Kola Peninsula and the Ilímaussaq alkaline complex in southern Greenland.