Apophyllite forms in clear, prismatic crystals that look like a stacks of glass. Green is the rarest color. It is found in volcanic regions and forms in caviti — Photo: Steve Jurvetson · CC BY 2.0
Fluorapophyllite-(K)
Also known as: Apophyllite.
Fluorapophyllite-(K), formerly known as apophyllite-(KF) and sometimes simply referred to as fluorapophyllite, is the most common mineral of the apophyllite group, with the chemical formula of KCa4Si8O20(F,OH)·8(H2O). It gets the first part of its name, "fluor", because it contains more fluorine than hydroxide compared to the other minerals in the apophyllite group. Fluorapophyllite crystallizes in the tetragonal crystal system. Tetragonal minerals have three axes of different lengths and angles of 90 degrees. Fluorapophyllite is an anisotropic mineral and has low relief.
Intro adapted from Wikipedia (CC BY-SA).
Fluorapophyllite-(K) is an IMA-recognized mineral species in the silicate class, with the chemical formula KCa₄Si₈O₂₀F·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 2.35; typically colorless or white or green or pink or yellow; white streak; pearly luster; refractive index 1.536; optically uniaxial.
IMA symbol Fapo-K, IMA status: approved, named in 1806.
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