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apophyllite

  (ə-pŏf'ə-līt', ăp'ə-fĭl'īt') pronunciation
n.

A white, pale pink, or pale green crystalline mineral, essentially KCa4Si8O20(F,OH)·8H2O.


 
 

A hydrous calcium-potassium silicate containing fluorine. The composition is variable but approximates to KFCa4(Si2O5)4 · 8H2O. It resembles the zeolites, with which it is sometimes classified, but differs from most zeolites in having no aluminum. It exfoliates (swells) when heated, losing water, and is named from this characteristic; the water can be reabsorbed. It is essentially white, with a vitreous luster, but may show shades of green, yellow, or red. The symmetry is tetragonal, and the crystal structure contains sheets of linked SiO4 groups; this accounts for the perfect basal cleavage of the mineral. It occurs as a secondary mineral in cavities in basic igneous rocks, commonly in association with zeolites. The specific gravity is about 2.3–2.4, the hardness 4.5–5 on Mohs scale, the mean refractive index about 1.535, and the birefringence 0.002. See also Silicate minerals; Zeolite.


 
Rock & Mineral Guide: apophyllite

(K,Na)Ca
Tetragonal -- Ditetragonal bipyramidal

Environment

Though technically not a zeolite, associated with them in traprocks and in some ore veins.

Crystal description

Practically always in crystals, frequently distinct individuals, varying from the common, short-prismatic habit with a more or less well-formed pyramidal truncation to simple, blunt, square prisms, pseudocubes. Tabular habit rare. Often over an inch or two (3-5 cm or more) across, or in 2-in.-long (5 cm) prisms. Prism faces have parallel vertical lines; base has a very pearly look.

Physical properties

Colorless, white, pale pink, pale to emerald green. Luster glassy and pearly; hardness 4Ɖ-5; specific gravity 2.3-2.4; fracture uneven; cleavage perfect basal. Brittle and a bit fragile from the ready cleavage; transparent to translucent.

Composition

Alkaline calcium, potassium fluosilicate (5.2% K 2 O, 25.0% CaO, 53.7% SiO 2 , 16.1% H 2 O, with the fluorine replacing some of the oxygen). Sometimes variants are given the subspecies names hydroxyapophyllite, fluorapophyllite, and natroapophyllite.

Tests

Fuses easily, bubbling and swelling to a white vesicular enamel. The depths of the mass fluoresce weak greenish white after heating.

Distinguishing characteristics

The different (pearly) luster on the basal (cleavage) face distinguishes apophyllite from some cubic minerals such as fluorite that it might otherwise suggest. The typical square pyramid and prism combination with the two lusters is easy to recognize. In case of doubt, the basal cleavage makes the identity certain. Distinguished from stilbite and heulandite by less exuberant swelling, quicker melting with boiling, and the fluorescence usual after heating.

Occurrence

Found in typical, well-formed white crystals in the traprocks of Paterson, New Jersey, and Bay of Fundy, Nova Scotia, beaches. Beautiful 2-3-in. (5-8 cm) crystals on prehnite were found near Washington, D.C., at Fairfax, Virginia. It is also sometimes found in cavities in pegmatitic dikes, where it is one of the last minerals to form, and in ore veins. Two notable occurrences of the latter are the delicate pink prismatic crystals at Guanajuato, Mexico, and once in the Harz Mountains of Germany. Excellent tabular crystal clusters and "roses" were found at French Creek and Cornwall, Pennsylvania. Unusually clear, tabular crystals occur in the Michigan Upper Peninsula copper mines, with anal cime and datolite. Particularly large, fine, pale green crystals were found in a railway cut (and now in numerous quarries) in Santa Catarina, Brazil. Very clear ones have come from Iceland.



 
Wikipedia: apophyllite
Apophyllite
Hydroxyapophyllite.jpg
General
Category Mineral
Chemical formula (K,Na)Ca4Si8O20(F,OH) • 8H2O
Identification
Color Usually white, colorless; also blue, green, brown, yellow, pink, violet
Crystal habit prismatic, tabular, massive
Crystal system Tetragonal; Orthorhombic (natroapophyllite)
Cleavage [001] Perfect
Fracture Uneven
Mohs Scale hardness 4.5 - 5
Luster Vitreous; Pearly
Refractive index 1.536
Pleochroism Dichroic (colorless)
Streak White
Specific gravity 2.3 - 2.4
Diaphaneity Transparent to translucent

The name apophyllite refers to a specific group of phyllosilicate minerals, a class of minerals that also includes the micas. 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 fluorapophyllite, hydroxyapophyllite, and natroapophyllite. The name apophyllite is derived from the Greek apophylliso, meaning "it flakes off," a reference to this class's tendency flake apart when heated, due to water loss. These minerals are typically found as secondary minerals in basalt.

Though relatively unfamiliar to the general public, apophyllites are fairly prevalent around the world, with specimens coming from some of the worlds 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

Collectors

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.

Crystal Huggers

Apophyllites are considered important minerals in many new age practices[1], an easy association because they naturally form pyramids. They are considered beneficial in reiki healing, are thought to bring one in closer contact with the "spiritual realm", and to be good for channelling love and, conversely, for clarity of thought. They are supposed to vibrate the number 4[2].

Species of Apophyllite

  • Fluorapophyllite, (K, Na)Ca4Si8O20(F, OH) · 8H2O - white, colorless, yellow, green, violet
  • Hydroxyapophyllite, KCa4Si8O20(OH, F) · 8H2O - white, colorless
  • Natroapophyllite, (K, Na)Ca4Si8O20F · 8H2O - brown, yellow, colorless

References


 
 

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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Rock & Mineral Guide. Peterson Field Guide to Rocks and Minerals, by Frederick H. Pough. Copyright © 1998 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Apophyllite" Read more

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