Today we will talk about a real trickster among the kaolinite-group minerals – halloysite.
Why is halloysite so tricky?
Identifying kaolinite-group minerals is no easy task. Halloysite is particularly insidious: it easily "hides" within a mass of kaolinite. Even methods such as X‑ray diffraction or infrared spectroscopy sometimes cannot identify it unequivocally.
A striking demonstration of halloysite's "camouflage abilities" came from the Reynolds Cup 12 competition (2024). One sample contained a mixture of kaolinite with only 4% halloysite, which 65% of the competition participants did not detect. Although the proportion is small, it was possible to detect it – thanks to scanning electron microscopy (SEM). The SEM image clearly shows the characteristic halloysite tubes.
And in the "very tricky kaolinite" sample (from the Kyshtym deposit) provided by Irina Pavlova, a significant number of halloysite tubes were hiding beneath the mask of kaolinite (see images).
How can you find it?
To reliably identify halloysite, it is often necessary to combine methods:
SEM – helps to see the morphology (characteristic nanotubes);
Thermal analysis;
X‑ray diffraction (XRD);
IR spectroscopy.
The takeaway is this:
Not everything that looks like kaolinite is kaolinite.
The SEM images were taken by Mikhail Sergeevich Chernov, Candidate of Geological and Mineralogical Sciences (Lomonosov Moscow State University)