Fundamental Minerals

Sialic Minerals

Feldspars

Feldspathoids

Quartz

Femic Minerals

Spodumene

Accessory Minerals

Rare Accessory

Alteration Products

Microstructures

Rocks

Jacupiranga complex

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 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". The zeolites structure contains open channels (Fig.1) 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.

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.

Fig.1: Schematic structure of zeolites. Note the "hole" in the structure.

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.

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

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.

Photo
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)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)	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)
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)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
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)	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)	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)
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)	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)	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)
Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)	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)
Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
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)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 2x (Field of view = 7mm)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 1x (Field of view = 9mm)
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)	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)	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)
Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 2x (Field of view = 7mm)	Fibrous natrolite crystals (I order gray-yellow). Alkaline pegmatite from Sagåsen quarry, Tvedalen (Norway). XPL image, 2x (Field of view = 7mm)	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)
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)	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)	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)