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Allophane

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Formula:
(Al2O3)(SiO2)1.3-2 · 2.5-3H2O
System:
Amorphous
Colour:
White, pale blue to ...
Lustre:
Waxy
Hardness:
3
Name:
From the Greek άλλος ("allos") for "other" or "different" and φαίνεσθαι ("phaenesthai"), "to appear", in allusion to the change it undergoes in a blowpipe flame.
Amorphous hydrous silicate of aluminium, composition not fixed. Principal member of the nominal "Allophane Group."
Copper-bearing varieties can be confused with chrysocolla.
Colourless varieties may be confused with hyalite.

The nano-sized particles have a ball-shaped morphology.

Related to imogolite.


Classification of Allophane

Approved, 'Grandfathered' (first described prior to 1959)
9.ED.20

9 : SILICATES (Germanates)
E : Phyllosilicates
D : Phyllosilicates with kaolinite layers composed of tetrahedral and octahedral nets
Dana 7th ed.:
71.1.5.1
71.1.5.1

71 : PHYLLOSILICATES Sheets of Six-Membered Rings
1 : Sheets of 6-membered rings with 1:1 layers
15.11

15 : Silicates of Aluminum

Physical Properties of Allophane

Diaphaneity (Transparency):
Transparent, Translucent
Colour:
White, pale blue to sky-blue, green, brown
Streak:
White
Hardness (Mohs):
3
Tenacity:
Brittle
Cleavage:
None Observed
None
Fracture:
Conchoidal

Chemical Properties of Allophane

Formula:
(Al2O3)(SiO2)1.3-2 · 2.5-3H2O
IMA Formula:
Al2O3(SiO2)1.3-2.0 · 2.5-3.0H2O
Elements listed in formula:
Common Impurities:
Ti,Fe,Mg,Ca,Na,K

Crystallography of Allophane

Crystal System:
Amorphous
Morphology:
Rarely observed as ring-shaped particles, with diameters of 50 ºA, which in three dimensions may represent sections through hollow spherules or polyhedra. As hyaline crusts and masses; stalactites and flowstones.

Occurrences of Allophane

Type Occurrence of Allophane

Place of Conservation of Type Material:
Mining Academy, Freiberg, Germany, 26104.

Relationship of Allophane to other Species

9.ED.Clinochrysotile
9.ED.05DickiteAl2(Si2O5)(OH)4
9.ED.05KaoliniteAl2(Si2O5)(OH)4
9.ED.05NacriteAl2(Si2O5)(OH)4
9.ED.05Odinite(Fe,Mg,Al,Fe,Ti,Mn)2.4((Si,Al)2O5)(OH)4
9.ED.10HalloysiteAl2(Si2O5)(OH)4
9.ED.10HisingeriteFe23+(Si2O5)(OH)4 · 2H2O
9.ED.10Halloysite-7ÅAl2(Si2O5)(OH)4
9.ED.15AmesiteMg2Al(AlSiO5)(OH)4
9.ED.15AntigoriteMg3(Si2O5)(OH)4
9.ED.15Berthierine(Fe2+,Fe3+,Al)3(Si,Al)2O5(OH)4
9.ED.15Brindleyite(Ni,Al)3(Si,Al)2O5(OH)4
9.ED.15CaryopiliteMn32+Si2O5(OH)4
9.ED.15ChrysotileMg3(Si2O5)(OH)4
9.ED.15CronstedtiteFe22+Fe3+((Si,Fe3+)2O5)(OH)4
9.ED.15Fraipontite(Zn,Al)3((Si,Al)2O5)(OH)4
9.ED.15Greenalite(Fe2+,Fe3+)2-3Si2O5(OH)4
9.ED.15KellyiteMn22+Al(AlSiO5)(OH)4
9.ED.15LizarditeMg3(Si2O5)(OH)4
9.ED.15ManandoniteLi2Al4(Si2AlB)O10(OH)8
9.ED.15Népouite(Ni,Mg)3(Si2O5)(OH)4
9.ED.15PecoraiteNi3(Si2O5)(OH)4
9.ED.15GuidottiiteMn2Fe3+(Fe3+SiO5)(OH)4
9.ED.20ChrysocollaCu2-xAlx(H2-xSi2O5)(OH)4 · nH2O
9.ED.20ImogoliteAl2SiO3(OH)4
9.ED.20Neotocite(Mn,Fe,Mg)SiO3 · H2O
9.ED.25BismutoferriteFe23+Bi(SiO4)2(OH)
9.ED.25ChapmaniteFe23+Sb3+(Si2O5)O3(OH)
15.1AndalusiteAl2(SiO4)O
15.2KyaniteAl2(SiO4)O
15.3SillimaniteAl2(SiO4)O
15.4MulliteAl4+2xSi2-2xO10-x
15.5PyrophylliteAl2Si4O10(OH)2
15.6DickiteAl2(Si2O5)(OH)4
15.7NacriteAl2(Si2O5)(OH)4
15.8KaoliniteAl2(Si2O5)(OH)4
15.9MetahalloysiteAl2(Si2O5)(OH)4
15.10HalloysiteAl2(Si2O5)(OH)4

Other Names for Allophane

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Allophane

Reference List:
Hausmann, J.F.L., Stromeyer, F. (1816) Über Silberkupferglanz und Allophan. Göttingische Gelehrte Anzeigen: 2: 1251-1253.

Snetsinger, K.G. (1967) High-alumina allophane as a weathering product of plagioclase. American Mineralogist: 52: 254-262.

Kitagawa, Y. (1974) Dehydration of allophane and its structural formula. American Mineralogist: 59: 1094-1098.

Henmi, T., Wada, K. (1976) Morphology and composition of allophane. American Mineralogist: 61: 379-390.

Wada, S.I., Wada, K. (1977) Density and structure of allophane. Clay Minerals Bulletin: 12: 289-298.

Bailey, S.W. (1980) Summary of recommendations of AIPEA nomenclature committee on clay minerals. American Mineralogist: 65: 1-7.

Parfitt, R.L., Furkert, R.J., Henmi, T. (1980) Identification and structure of two types of allophane from volcanic ash soils and tephra. Clays and Clay Minerals: 28: 328-334.

van der Gaast, S.J., Wada, K., Wada, S.I., Kakuto, Y. (1985) Small-angle X-ray powder diffraction, morphology, and structure of allophane and imogolite. Clays and Clay Minerals: 33: 237-243.

Gaines, R.V., H. Skinner, C.W., Foord, E.E., Mason, B., Rosenzweig, A. (1997) Dana's New Mineralogy : The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana: eighth edition. John Wiley and Sons, Inc., 1819 pp.: 1432.

Internet Links for Allophane

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https://www.mindat.org/min-139.html
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Specimens:
The following Allophane specimens are currently listed for sale on minfind.com.

Localities for Allophane

Mineral and/or Locality  
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