Cleavelandite

Cleavelandite is a habit variety of albite, the sodium end-member of the plagioclase feldspar series. Rather than forming blocky crystals, it grows as thin, curved, leaf-like blades that fan out into rosettes and crested aggregates, giving it an unmistakable lamellar appearance.

It is almost always snow-white and translucent, and it is a hallmark mineral of evolved granite pegmatites. Collectors prize it both for its sculptural form and because it frequently hosts spectacular crystals of tourmaline, lepidolite, beryl, and rare phosphate minerals.

Named after the American mineralogist Parker Cleaveland, it is chemically identical to ordinary albite but distinguished entirely by its platy growth style.

Cleavelandite forms in the late, volatile-rich stages of granite pegmatite crystallization. As a pegmatite cools and its residual melt becomes enriched in sodium, fluorine, and other fluxes, albite recrystallizes into characteristic platy blades that replace earlier potassium feldspar and line miarolitic cavities.

Its thin, bladed habit is thought to reflect rapid growth from a fluxed, water-rich fluid. It commonly appears alongside elbaite tourmaline, spodumene, amblygonite, and lithium micas. Classic localities include the pegmatites of Maine and California (USA), Minas Gerais (Brazil), Pala in San Diego County, and pegmatite districts in Afghanistan and Pakistan.

Look for thin, curved, blade-like white crystals stacked or fanned into crested, book-like aggregates - this platy habit is the single most diagnostic feature. Hardness is 6-6.5 (it will scratch glass), luster is vitreous to pearly on cleavage faces, and the streak is white.

It can resemble platy barite or muscovite, but cleavelandite is harder than mica and far less dense than barite. Unlike blocky orthoclase, it shows no simple Carlsbad twins; instead albite twinning produces fine striations. Its association with tourmaline and lithium minerals in pegmatites is a strong contextual clue.

Cleavelandite has little industrial use on its own, though as albite it is part of the feldspar raw material used in ceramics and glassmaking. Its real value is to mineral collectors, who seek well-formed bladed aggregates and the gem crystals it cradles.

Specimens hosting pink tourmaline, aquamarine, or morganite on a bed of white cleavelandite blades are among the most desirable pegmatite display pieces and can command high prices. It has no significant metaphysical tradition distinct from albite or moonstone.