Apophyllite

Extended geology

Apophyllite is a group name covering a few closely related species, chiefly fluorapophyllite and hydroxyapophyllite, distinguished by whether fluorine or hydroxyl dominates one site in the structure. All are sheet silicates of potassium and calcium with water molecules held in the lattice, which is what gives the group its defining behavior of flaking apart when heated.

Crystals form in the tetragonal system, commonly as pseudo-cubic prisms capped by steep pyramids, and show perfect cleavage parallel to the base. Specific gravity is around 2.3 to 2.4 and hardness 4.5 to 5, both on the low side. The luster is vitreous on prism faces and distinctly pearly on the cleavage surface, a useful identifying feature.

Extended sourcing

The Deccan Traps of western India are the premier source, where vast flood-basalt flows around Pune and Jalgaon are riddled with gas cavities that host apophyllite alongside stilbite, heulandite, and other zeolites. Quarrying for construction stone regularly opens fresh pockets, which keeps fine Indian specimens on the market.

Other notable localities include Brazil, the Harz Mountains of Germany, Iceland, the Faroe Islands, Canada, and parts of the United States. Most occurrences share the same basic recipe of apophyllite growing in volcanic cavities, so specimen quality and associated minerals, more than country alone, drive desirability.

Authentication and warning signs

Look for glassy tetragonal crystals with a pearly base cleavage, often on a matrix of zeolites, and a hardness low enough that a steel blade will mark it. Green apophyllite should show a soft, natural, slightly uneven green from trace elements, not the flat saturated tone of a dye. Clear apophyllite differs from quartz in its softer feel, easy cleavage, and blockier, pyramid-capped habit.

Outright fakery is uncommon because apophyllite is affordable, but mislabeling within the zeolite world is not. A seller who names the species and the Indian locality, and who distinguishes apophyllite from the stilbite or heulandite it grows on, is a good sign.

History and folklore

Apophyllite was named in the early nineteenth century by the French mineralogist Rene Just Hauy, from the Greek words meaning to flake off, after its habit of exfoliating under heat. For most of its history it was a mineralogist's and collector's stone rather than a folk talisman.

Its metaphysical reputation is recent, growing with the flood of fine Indian specimens into the global crystal market. Because that reputation formed in modern times, apophyllite carries contemporary associations of clarity and spiritual connection rather than old traditional lore.

Varieties and trade names

Clear or white apophyllite: the most common, glassy transparent to milky pyramids and prisms, often on stilbite.

Green apophyllite: colored by trace elements, ranging from pale mint to deeper green, especially prized from India.

Fisheye stone: an older name referring to the pearly reflection seen down the cleavage face of some crystals.

Pink and other tinted apophyllite: uncommon, collected for rarity.

What it costs in the market

Apophyllite is one of the more affordable fine specimen minerals. Small clear points and clusters are inexpensive, while larger plates, well-formed green crystals, and dramatic combinations with stilbite or other zeolites climb into higher prices. Value is driven by crystal size and clarity, color, condition of the fragile tips, and the quality of the overall specimen.