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Sounion Mine No. 06 ("Exi Mine"), Agia Varvara Mines (St Barbara Mines), Sounion Area, Lavrion District Mines, Lavrion District (Laurion; Laurium), Attikí Prefecture (Attica; Attika), Greece
© Steve Rust
|System:||Monoclinic||Colour:||White to tan, sometimes ...|
|Hardness:||1 - 2|
Typically found as earthy to somewhat waxy looking extremely fine-grained clayey masses, white to tan and also occassionally bluish or greenish.
The name halloysite stands for the two grandfathered and distinct species Halloysite-7Å and Halloysite-10Å.
Halloysite-10Å is also known as "endellite" in European literature and considered to be a hydrated mineral - the "hydrated halloysite" of North American literature.
"Metahalloysite" (= Halloysite-7Å) is dehydrated halloysite, and characterised by a reduced interlayer spacing.
Originally reported from Angleur, Liège, Liège Province, Belgium.
Classification of Halloysite
|IMA status:||Not Approved|
|Explanation of status:||Confusion exists between "halloysite" and "endellite." Most European literature has "halloysite" as Al2Si2O5(OH)4 · 2H2O (= Halloysite-10Å) and calls it "endellite." Most North American literature (not Dana 8th...) has it as Al2Si2O5(OH)4 (= Halloysite-7Å) - with the hydrated variety.|
|Strunz 8th edition ID:||8/H.25-40|
|Nickel-Strunz 10th (pending) edition ID:||9.ED.10|
9 : SILICATES (Germanates)
E : Phyllosilicates
D : Phyllosilicates with kaolinite layers composed of tetrahedral and octahedral nets
|Dana 7th edition ID:||18.104.22.168|
|Dana 8th edition ID:||22.214.171.124|
71 : PHYLLOSILICATES Sheets of Six-Membered Rings
1 : Sheets of 6-membered rings with 1:1 layers
|Hey's CIM Ref.:||15.10|
15 : Silicates of Aluminum
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Occurrences of Halloysite
|Geological Setting:||Halloysite is found in widely varied environments, including as an alteration of basaltic rocks, in hydrothermally altered fissure deposits in monzonites; it is also derived from feldspars, chlorites, micas, rhyolites, granites, volcanic ash, tuffs and pumices. More rarely found in granitic pegmatites, bauxites or laterites, and in some marine and glacial clays.|
Physical Properties of Halloysite
|Diaphaneity (Transparency):||Translucent, Opaque|
|Colour:||White to tan, sometimes greenish or bluish, also chocolate brown to reddish.|
|Streak:||Paler than the color, or white.|
|Hardness (Mohs):||1 - 2|
|Density (measured):||2 - 2.65 g/cm3|
|Density (calculated):||2.14 g/cm3|
Crystallography of Halloysite
|Class (H-M):||m - Domatic|
|Cell Parameters:||a = 5.14Å, b = 8.9Å, c = 7.214Å|
β = 99.7°
|Ratio:||a:b:c = 0.578 : 1 : 0.811|
|Unit Cell Volume:||V 325.29 Å³ (Calculated from Unit Cell)|
|Morphology:||Typically found as extremely fine-grained clayey masses. The two "forms" Halloysite-7Å and Halloysite-10Å are the most common. It has a tubular morphology at the nanometer scale.|
|X-Ray Powder Diffraction:|
Optical Data of Halloysite
|RI values:||nα = 1.553 - 1.565 nβ = 1.559 - 1.569 nγ = 1.560 - 1.570|
|Maximum Birefringence:||δ = 0.007|
Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
|Dispersion:||r < v moderate|
Chemical Properties of Halloysite
|Simplified for copy/paste:||Al2(Si2O5)(OH)4|
|Essential elements:||Al, H, O, Si|
|All elements listed in formula:||Al, H, O, Si|
Relationship of Halloysite to other Species
|Member of:||Kaolinite-Serpentine Group|
|Other Members of Group:|
|Related Minerals - Nickel-Strunz Grouping):|
|Related Minerals - Hey's Index Grouping:|
|Related Minerals - Dana Grouping):|
Other Names for Halloysite
|Health Warning:||No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.|
|Industrial Uses:||Used in applications similar to those of kaolinite, such as high-strength cements and high-quality ceramics.|
References for Halloysite
Clays and Clay Minerals (1978): 26: 25.
Gaines, Richard V., H. Catherine, W. Skinner, Eugene E. Foord, Brian Mason, Abraham Rosenzweig (1997), Dana's New Mineralogy : The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana: 1411.
Internet Links for Halloysite
Localities for Halloysite
The map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.