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Silicate

Fluorapophyllite-(NH_4_)

(NH₄)Ca₄(Si₈O₂₀)F·8H₂O
Hardness4.5–5
Crystal systemTetragonal
ClassSilicate
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Fluorapophyllite-(NH_4_)

Fluorapophyllite-(NH_4_) is an IMA-recognized mineral species in the silicate class, with the chemical formula (NH₄)Ca₄(Si₈O₂₀)F·8H₂O.

It crystallizes in the tetragonal crystal system (space group P4/mnc). It is a member of the Apophyllite structural group.

Key properties: Mohs hardness 4.5–5; specific gravity 2.325; White streak; Vitreous to pearly luster; optically uniaxial.

IMA symbol Fapo-NH4, IMA status: approved, named in 2020.

Found in cavities of quartz-illite-saponite-tobelite xenoliths embedded in pyroxene andesite. A hydrothermal mineral, formed at a late stage of auto-hydrothermal alteration.

It is found associated with Calcite, tridymite, pyrite, chabazite-Ca, heulandite-Ca.

The prefix indicates the NH4-dominant analogue of fluorapophyllite-(K), fluorapophyllite-(Na) and fluorapophyllite-(Cs).

Index entry. This entry combines official IMA/RRUFF species data with published physical-property data — a full written entry hasn’t been published yet. Browse more F minerals or help write this entry.