see link

http://www.webmineral.com/data/Halloysite.shtml#.WLrvJRh2lGw

Thanks Ian for the link

Dear Anish,

A good and relatively easy way to get the chemical composition of your halloysite minerals would be edx via sem or similar methods. You will get the quantification of most chemical elements from single cristals. If you use xrf you normally measure the bulk composition of your sample which means if you have a heterogeneous material this will lead to an average composition. 

Cheers

Max

See attached files

Thank you so much Max

X-ray photoelectron spectroscopy (XPS) also gives the elemental composition. In my opinion, XPS is better than EDS. 

If you are not sure of the elements present, first go for the EDS (Since you have to mention the elements present for XPS). And then, go for XPS. 

Dear Mr. Philip:

Halloysite has a similar chemical composition as kaolinite but contains additional water molecules between the layers, leading to the formula Al2Si2O5(OH)4 . 2H2O in its fully hydrated form. In the kaolinite polymorphs the water content of water stands at 13.96 wt. % H2O, in halloysite it is higher and  lies in the range 14.3 wt. % to 15.35 wt. % H2O (Weaver, 1989). The halloysite-(10 Å) typically accommodates  interlayer water which distinguishes it from the other kaolinite-group polymorphs in  kaolin group and irreversibly dehydrates to a 7 Å structure (Joussein et al., 2005; Churchman et al., 2010).

According to Weaver (1989) the less hydrous form of halloysite Al2SiO2O5(OH)4 is akin to kaolinite with a basal spacing near 7.2 Å, the more hydrous form of Al2SiO2O5(OH)4 . 2H2O has a basal spacing of 10.1 Å. Halloysite (10 Å) transforms to halloysite (7 Å) at about 70°C. Since halloysite loses its interlayer water very easily it is often found in nature  in a partly dehydrated state.  This dehydration process is not observed with the three kaolinite 7-Å polymorphs. Fully hydrated halloysite-(10 Å) will not pose any problems  on the identification of this phyllosilicate besides kaolinite-group minerals which it accompanies in kaolin. A gradual loss of the interlayer water, leading to its 7-Å metaform is very common in nature, as in many other mineral groups such as the "uranyl mica-group". Therefore a precise determination of halloysite needs some solvation of the clay sized fractions with ethylene glycol to diagnose halloysite, a procedure not very uncommon in the proper identification of expandable phyllosilicates of the smectite group (Hillier and Ryan, 2002). As an alternative Joussein et al. (2007) proposed some formamide treatment. Other solvent or reactive substances are dimethyl sulfoxide, potassium acetate, urea and hydrazine (Wada, 1961; Churchman and Carr, 1973; Mellouk et al., 2009; Nicolini et al. 2009; Horvath et al. 2011).  A thermodynamical modeling of the equilibria as function of water and dissolved silica activities has been performed by Trolard et al. (1990). In nature specimens of halloysite do not significantly differ from those of kaolin made up predominantly of kaolinite polymorphs.  Under the SEM and TEM the morphological differences are striking and facilitate its identification. It shows a characteristic hollow tubular hydrated morphology. It can change into spheroidal halloysites or plates described by Askenasy  et  al. (1973) and by  Dixon  and  McKee (1974).

Halloysite has a cation exchange capacity which stands at 5 meq/ 100 gr, whereas  that of smectite (Wyoming Bentonite ranges from 75 to 100 meq/100 gr.). The low CEC is caused by OH-groups (= edge-effects). For comparison only, its closest relative kaolinite from Georgia Kaolin has a CEC of 1 to 2 meq/100 gr.

Further information on the origin and distribution of halloysite see:

DILL, H.G. (2016) Kaolin: soil, rock and ore From the mineral to the magmatic, sedimentary, and metamorphic environments.- Earth Sciences Reviews 161: 16-129.

Best regards

H.G.Dill