Anorthoclase Crystal — Mt Erebus, Ross Island, Antarctica

Anorthoclase crystal from Mount Erebus, Antarctica

This rare Antarctic mineral specimen features natural anorthoclase collected from Mount Erebus, one of the most scientifically famous volcanoes on Earth. Its combination of mineral identity, extreme locality, and volcanic context makes it a highly distinctive collector piece.

Mount Erebus Anorthoclase Crystal – Classic “Erebus Feldspar”

This ultra-rare anorthoclase feldspar crystal came from the slopes of Mount Erebus, Ross Island, Antarctica — the southernmost active volcano on Earth. Its elongated prismatic form, grey-white etched surface, and patches of attached vesicular lava match the classic morphology described by Frank Debenham during Scott’s famous 1910–13 Terra Nova Expedition.

Type Locality: Mount Erebus, Ross Island

Collected from the Erebus Volcanic Province, where loose anorthoclase phenocrysts mantle the crater slopes. These crystals are historically linked to the same field region documented by Debenham during early Antarctic exploration.

Scientific Lineage

The optical and chemical characteristics of Erebus anorthoclase were established by E. D. Mountain (1925, Mineralogical Magazine). His work confirmed that these feldspars are Na–K alkali feldspar with an approximate specific gravity of 2.62 and 2V ≈ 62°. Literature reference: Mountain, E. D. (1925). “Potash-oligoclase from Mt. Erebus, Antarctica, and anorthoclase from Mt. Kenya, East Africa.” Mineralogical Magazine, 20, 331–345.

Crystal Habit, Surface Texture

Elongate, thick-prismatic crystal with tapered ends—entirely consistent with classic Erebus feldspar phenocrysts.

A strongly weathered grey-white, naturally etched surface produced by long-term exposure and abrasion within phonolitic ejecta on the crater slopes.

Dark, vesicular lava patches (phonolite/kenyte fragments) fused to the crystal surface—a hallmark indicator of the volcano Mount Erebus ejecta.

Irregular but directional breaks that align with the two feldspar cleavages near 90°, typical of anorthoclase.

Specimen Details

Collector's Value

Mount Erebus is the type locality for unusually large and distinctive anorthoclase crystals. This specimen bridges the heroic-era Antarctic expeditions and the modern scientific understanding of alkaline volcanism. Its fusion of historic provenance, mineralogical importance, and a lineage in polar exploration makes it an outstanding centerpiece for any advanced mineral or "mini-museum" collection.

Add to Your Collection

A rare, historically anchored Antarctic anorthoclase crystal from one of the southernmost iconic volcanic sites on Earth—ready to become the highlight in any elite geological collection. Only 1 available.