The name apophyllite refers to a specific group of

phyllosilicates Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

, a class of minerals. Originally, the group name referred to a specific mineral, but was redefined in 1978 to stand for a class of minerals of similar chemical makeup that comprise a

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

series, and includes the members fluorapophyllite-(K), fluorapophyllite-(Na), hydroxyapophyllite-(K). The name apophyllite is derived from the

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ἀποφυλλίζω ''apophylliso,'' meaning "it flakes off", a reference to this class's tendency to flake apart when heated, due to water loss. Exfoliation of apophyllite is also possible by treating it with acids or simply by rubbing it. These minerals are typically found as secondary minerals in

vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features o ...

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

or other volcanic rocks. A recent change (2008) in the nomenclature system used for this group was approved by the

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. Th ...

, removing the prefixes from the species names and using suffixes to designate the species.Burke, E.A.J. (2008): Tidying up mineral names: an IMA-CNMNC scheme for suffixes, hyphens and diacritical marks. Mineral. Rec., 39, 131–13

/ref> A subsequent nomenclature change approved by the International Mineralogical Association in 2013 renamed the minerals to include both suffixes and prefixes, as shown above. Though relatively unfamiliar to the general public, apophyllites are fairly prevalent around the world, with specimens coming from some of the world's most well-known mineral localities. These localities include:

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; the

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, and

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, with other locations in

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, and throughout the

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Structure

Apophyllite has an unusual structure for a phyllosilicate. Whereas most phyllosilicates have a T layer (silica backbone) consisting of interlocked 6-fold rings of silica tetrahedra, with pseudohexagonal symmetry, the T layer in apophyllite consists of interlocked 4-fold and 8-fold rings of silica tetrahedra with true tetragonal symmetry. File:Apophyllite T.png, T layer (silica backbone layer) of apophyllite File:Apophyllite 100.png, Structure of apophyllite viewed in the direction, parallel to layering File:Apophyllite unit cell.png, Unit cell of apophyllite

Species of apophyllite

* Fluorapophyllite-(K) (formerly fluorapophyllite, apophyllite-(KF)), KCa₄Si₈O₂₀(F,OH)·8H₂O - white, colorless, yellow, green, violet *Hydroxyapophyllite-(K) (formerly hydroxyapophyllite, apophyllite-(KOH)), KCa₄Si₈O₂₀(OH,F)·8H₂O - white, colorless *Fluorapophyllite-(Na) (formerly natroapophyllite, apophyllite-(NaF)), NaCa₄Si₈O₂₀F·8H₂O - brown, yellow, colorlessApophyllite-(NaF) on Mindat
/ref> *Fluorapophyllit-(Cs) (new) CsCa₄(Si₈O₂₀)F·8H₂O *Fluorapophyllit-(NH4) (new) NH₄Ca₄(Si₈O₂₀)F⋅8H₂O , Format: PDF, KBytes: 623 Apophyllite-(KF)-66684.jpg, Isolated Fluorapophyllite-(K) cluster on contrasting matrix Hydroxyapophyllite on white background.jpg, Hydroxyapophyllite Natroapophyllite-ind11b.jpg, Fluorapophyllite-(Na)

References

MinDat Listing

* * This describes the older definition as a specific mineral. {{refend Phyllosilicates Sodium minerals Potassium minerals Calcium minerals Tetragonal minerals Minerals in space group 128 Fluorine minerals

Structure

Species of apophyllite

See also

References