Vugs in an iron meteorite

Primary and Secondary Structures - Meteorites
New England Meteoritical Services

Drusy vugs in an iron meteorite

Albion - IVA Iron, fine octahedrite.

Figure 1. Scale bar 2.6 mm.

Albion, IVA, iron, fine octahedrite. Vug lined with druzy mineralogy.

Drusy Vugs in Iron Meteorites:
The Exceptional Case of Albion (IVA, Fine Octahedrite)

Figure 1. Drusy vug in the Albion iron meteorite (IVA, fine octahedrite), lined with spheroidal mineral aggregates.
Scale bar=2.6 mm.

Figure 2. Interior of a vug in Albion showing blocky, euhedral daubréelite grains and rounded euhedral to subhedral grains of a new phosphide mineral within the spheroids. Scale bar=1.5 mm.

Figure 3. Additional view of drusy vug in Albion. Scale bar=2.6 mm.

Vugs and Drusy Mineralization
Drusy vugs—small cavities lined with euhedral to subhedral crystals—are common in terrestrial igneous, sedimentary, and metamorphic rocks, where they typically form through dissolution along fractures or by gas entrapment during crystallization. In iron meteorites, however, such open cavities are exceptionally rare, as the high-density metallic matrix and slow cooling in parent-body cores generally favor compact, inclusion-filled textures rather than void spaces.

The Albion meteorite (IVA group, fine octahedrite) is unique among known iron meteorites in hosting well-developed vugs lined with drusy spheroidal mineral aggregates. These features raise important questions regarding their origin—specifically, whether they are primary (formed during initial solidification and cooling) or secondary (produced by later processes such as shock or alteration).

Origin and Formation
Evidence strongly favors a primary origin for the vugs in Albion. The meteorite exhibits cracks, voids, and imperfectly sealed grain boundaries that likely served as conduits for hot fluids or gaseous vapors during or shortly after core crystallization. These fluids mobilized troilite (FeS), fractionated nickel, and facilitated the precipitation of drusy spheroids on vug walls. This scenario is consistent with localized volatile activity or incomplete metal consolidation in the IVA parent body, which is known for its distinctive cooling history and structural variability among fine octahedrites.

A secondary, shock-induced origin—where hypervelocity impacts created cavities through melting or fracturing—appears less likely. Shock processes in iron meteorites typically produce diagnostic deformation features, including distorted Widmanstätten lamellae, Neumann bands, recrystallization, or subgrain development in kamacite and taenite. No such shock effects have been observed in the surrounding metal matrix of Albion, supporting the interpretation of the vugs as primary structures.

Mineralogy of the Drusy Linings
The spheroidal drusy aggregates lining the vugs contain:
• Blocky, euhedral grains of daubréelite (FeCr₂S₄)
• Rounded euhedral to subhedral grains of a previously unidentified phosphide mineral

These phases indicate complex fluid chemistry involving sulfur, chromium, and phosphorus mobility during vug formation. Such mineralization provides rare direct evidence of late-stage volatile or fluid processes in metallic parent-body environments.

Significance
Albion’s drusy vugs represent a singular petrographic anomaly among iron meteorites. They expand our understanding of the diversity of conditions within asteroidal cores, particularly the role of volatiles and fluid phases in otherwise reduced, metal-dominated systems. Further studies using modern techniques (e.g., high-resolution SEM, electron probe microanalysis, and Raman spectroscopy) could better constrain formation temperatures, fluid compositions, and the timing relative to Widmanstätten pattern development.

The specimen highlights the scientific value of ungrouped or anomalous members within established chemical groups like IVA, which themselves record unusual cooling rates potentially linked to parent-body disruption and reassembly.

Figure 2. Scale bar 1.5 mm.

Albion, IVA, iron, fine octahedrite.

Vug interior. Daubreelite occures in blocky, euhedral grains in the spheroids. A new phosphide mineral occuring in rounded euhedral to subhedral grains was also found in the spheroids. (1).

Figure 3. Scale bar 2.6 mm.

Albion, IVA, iron, fine octahedrite with druzy vugs..

References
1. Marvin, U. B., Petaev, M. I., & Kempton, R. W. (1996). Abstract, Lunar and Planetary Science XXVII, 821.
2. Kempton, R. W. (1995). Meteorite!, November issue.
3. Buchwald, V. F. (1975). Handbook of Iron Meteorites. University of California Press. (Context on IVA irons and general structures.)
• Additional context from meteoritical literature on fluid processes and vugs in metallic meteorites.

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