Apophyllite

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Apophyllite
Apophyllite Photolitherland.jpg
General
CategoryPhyllosilicate
Formula
(repeating unit)
(K,Na)Ca4Si8O20(F,OH)·8H2O
Identification
ColorUsually white, colorless; also blue, green, brown, yellow, pink, violet
Crystal habitPrismatic, tabular, massive
Crystal systemTetragonal; (Apophyllite-(NaF) is orthorhombic)
CleavagePerfect on [001]
FractureUneven
Mohs scale hardness4.5 - 5
LusterVitreous; pearly
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.3 – 2.4
Refractive index1.536
PleochroismDichroic (colorless)
References[1]
 
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Apophyllite
Apophyllite Photolitherland.jpg
General
CategoryPhyllosilicate
Formula
(repeating unit)
(K,Na)Ca4Si8O20(F,OH)·8H2O
Identification
ColorUsually white, colorless; also blue, green, brown, yellow, pink, violet
Crystal habitPrismatic, tabular, massive
Crystal systemTetragonal; (Apophyllite-(NaF) is orthorhombic)
CleavagePerfect on [001]
FractureUneven
Mohs scale hardness4.5 - 5
LusterVitreous; pearly
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.3 – 2.4
Refractive index1.536
PleochroismDichroic (colorless)
References[1]

The name apophyllite refers to a specific group of phyllosilicates, 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 series, and includes the members apophyllite-(KF), apophyllite-(KOH), and apophyllite-(NaF). The name apophyllite is derived from the Greek ἀπόΦυλλίςο apophylliso, meaning "it flakes off", a reference to this class's tendency to flake apart when heated, due to water loss. These minerals are typically found as secondary minerals in vesicles in basalt or other volcanic rocks. A recent change in the nomenclature system used for this group was approved by the International Mineralogical Association, removing the prefixes from the species names and using suffixes to designate the species.[2]

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: Poona, India; the Harz Mountains of Germany, Mont Saint-Hilaire in Canada, and Kongsberg, Norway, with other locations in Scotland, Ireland, Brazil, Japan, and throughout the United States.

Uses[edit]

Apophyllites are popular as collector's minerals. This popularity is due to a combination of factors, including their abundance, color variety, and well-defined crystals. Naturally forming pyramidal structures, they refract light in obvious rainbows, and can form "natural pyramids" when subjected to rock tumbling.

Species of Apophyllite[edit]

References[edit]


  • MinDat Listing
  • Mineral Galleries
  • Colville AA, Anderson CP, Black PM (1971). "Refinement of the crystal structure of apophyllite: I. X-ray diffraction and physical properties". American Mineralogist 56: 1222–1233.