Natrolite - Na2Al2Si3O10 * 2H2O

Natrolite was named in 1803 by Martin H. Klaproth from the Greek natron, "soda" in allusion to its sodium content and lithos, "stone."
Natrolite is the principal member of a group of zeolite minerals. Zeolites are hydrated aluminosilicate minerals made from interlinked tetrahedra of alumina (AlO4) and silica (SiO4). The zeolites structure contains open channels that allow water and large ions (such as sodium, potassium, and magnesium) to travel into and out of the crystal structure. Natrolite's structure contains chains of silicate tetrahedrons aligned in one direction; this produces the needle-like crystals. Its cleavage results from the weaker bonds between the chains.

The size of the channels controls the size of the molecules or ions, and therefore zeolites like natrolite can act as a chemical sieve. The term molecular sieve refers to a particular property of these materials: the ability to selectively sort molecules based primarily on a size exclusion process. This is due to a very regular pore structure of molecular dimensions.

The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been adsorbed by the material. Based on this, he called the material zeolite, from the Greek (zeo), meaning "to boil" and (líthos), meaning "stone".

Natrolite can be found in cavities and fractures in intermediate and basic magmatic rocks, particularly in volcanic rocks (e.g. in fractures in nepheline-phonolites). As an autometasomatic alteration product of feldspars and foids and is a common mineral in nepheline syenites.

Optical Properties:
Habit: Acicular to stalk-like parallel to the c-axis, fibrous to radiating and kidney-shaped.
Cleavage: Good on 110.
Color: Colourless, older crystals can be clouded.
Relief: Moderate.
Birefringence: Very low birefringence (white to straw-yellow interference colours of the I order).
Extinction: In longitudinal sections straight.

zeolite.jpg

schematic structure of zeolites. Note the "hole" in the structur.



diaspore(andy)(1).jpg

Panoramic view of a Diaspore-Natrolite Pegmatite. Image by Andy Tindle (Virtual Microscope). PPL image, field of view = 2.5cm. See also Diaspore-Natrolite - Virtual Microscope for more information on naujaite.




diaspore(andy)(2).jpg

Panoramic view of a Diaspore-Natrolite Pegmatite. Image by Andy Tindle (Virtual Microscope). XPL image, field of view = 2.5cm. See also Diaspore-Natrolite - Virtual Microscope for more information on naujaite.




Bibliography



• Deer, W.A., Howie, R.A., Zussman, J. (1998) Rock-forming Minerals.
• Optical Mineralogy : The Nonopaque Minerals by Phillips / Griffen
• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc
• Pichler, H., & Schmitt-Riegraf, C. (2012). Rock-forming minerals in thin section. Springer Science & Business Media.

Photo
natrolite(16).jpg

Fibrous natrolite crystals (colorless and with dusty appearance due to numerous inclusions). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). PPL image, 1x (Field of view = 9mm)
natrolite(17).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(19).jpg

Fibrous natrolite crystals (colorless and with dusty appearance due to numerous inclusions). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). PPL image, 1x (Field of view = 9mm)
natrolite(20).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(30).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(31).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(32).jpg

Fibrous natrolite crystals (colorless and with dusty appearance due to numerous inclusions). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). PPL image, 1x (Field of view = 9mm)
natrolite(33).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(40).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(42).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(43).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(55).jpg

Fibrous natrolite crystals (colorless and with dusty appearance due to numerous inclusions). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). PPL image, 1x (Field of view = 9mm)
natrolite(56).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(57).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(73).jpg

Fibrous natrolite crystals (colorless and with dusty appearance due to numerous inclusions). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). PPL image, 2x (Field of view = 7mm)
natrolite(74).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(75).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(76).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(91).jpg

Fibrous natrolite crystals (colorless and with dusty appearance due to numerous inclusions). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). PPL image, 2x (Field of view = 7mm)
natrolite(92).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 2x (Field of view = 7mm)
natrolite(97).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(99).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(100).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(103).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(105).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 2x (Field of view = 7mm)
natrolite(106).jpg

Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 2x (Field of view = 7mm)
natrolite(107).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 2x (Field of view = 7mm)
natrolite(116).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(117).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
natrolite(118).jpg

Fibrous natrolite crystals (I order gray-yellow) and Diaspore crystals (high birefringence). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)