26 July, 2015

Fithian Illite, lllinois, US

Fithian Illite at Salt Fork of Vermilion River near Fithian, IL

Illite is one of the most frequent clay minerals and is an important constituent of many sedimentary rocks. It was named after the state of Illinois, United States, by Grim, Bray and Bradley in 1937. The type locality of the Late Pennsylvania Fithian cyclothem is also the type locality of the clay mineral illite. In October 2013 I had the chance to actually visit the locality when participating in the 50th Anniversary Annual Meeting of the Clay Minerals Society at the University of Illinois at Urbana-Champaign. The trip was lead by Stephan Altaner and Shane Butler.

The image I made shows the succession of Pennsylvanian mudstone or underclay with carbonate concretions, and of course illite, towards a fossil soil horizon. Besides illite the mudstone also contains chlorite, kaolinite, illite-smectite, quartz and jarosite from pyrite weathering. The bituminous Flannigan coal is about 40 to 50 cm thick. Above it is a thinly bedded black shale and then marls & limestones. The sandstone units above and below the described sequence are not visible in the picture or obscured by the trees.

Fithian cyclothem with illite-bearing mudstone
Altaner & Butler, 2013: Geologic Field Trip to the Fithian Illite, Fithian, Illinois Guidebook for field trip held on October 10, 2013 in conjunction with the 50th Anniversary Annual Meeting of The Clay Minerals Society held at the University of Illinois at Urbana-Champaign

25 July, 2015

Let's XRD something unusual: What's in my ghassoul?

X-ray diffraction is an incredibly versatile method not restricted to rocks and minerals. While the material scientist and engineers among you might use it to examine concrete or thin-films in photovoltaics, I tried it on cosmetics from the organic supermarket. Actually, I picked a ready-to-use mixture of ghassoul that can be used as a shampoo. I will not disclose the brand or producer. But as far as I can tell from my very quick-and-dirty analysis: what is written on it - it is actually inside! But I make no guarantee!

Ghassoul is a natural clay rock found in the Atlas mountains of Morocco. Depending on the sources and literature it is either a bentonite, a stevensite-rich or a hectorite-rich clay rock. The clay has been mixed with oils, alcohol, and perfumes. So I was sceptical about identifying anything. I put the clay into a cup of water, stirred, and pipetted a few drops onto a glass slide to make an orientated texture mount. That is usually done for the clay fraction less than 2 microns and therefore probably only qualifies as playing around in the lab. 

The XRD trace was recorded from 2° to 70° 2θ and CuKα radiation. Measuring time is rather short with about 50 minutes. The characteristic peaks for several minerals are visible in the XRD trace. There is a large smectite 001 peak at about 14 Å and a small peak at about 1.52 Å characteristic for trioctahedral smectites. So this very likely contains a trioctahedral smectite such as hectorite, stevensite or saponite. I do not know if and how oils and perfumes intercalate into the smectite interlayer but assuming that they have not, the 001 position indicates an interlayer dominated by divalent cations, most likely Ca and Mg. If there would be Na or even K it would rather be around 10 to 12 Å.

XRD trace of ghassoul smear slide.
A lot of other peaks are visible at higher angles. I only marked the most important main peaks of easily recognisable phases, such as quartz, feldspar, calcite, mica, dolomite, and some kaolinite or chlorite. The later two are hard to distinguish without further work. There also are some peaks that would require more work, perhaps they are pyrite/hematite, more feldspar, etc. 

So, the ghassoul really does look like it contains natural clays and minerals! I cannot, however, determine if this is the natural composition or if minerals have been added.

Finally, as the stuff is very expensive I am putting it to practical trials on head and beard. :-)

13 July, 2015

Euroclay 2015

Yesterday I returned from the EuroClay 2015  in Edinbugh, UK. It was one of the largest clay science meetings in years - with over 500 participants. Topics ranged from rad waste, pharmaceutical applications to out of this world topics on Mars and its clay mineralogy. I, however, had the honor of starting the bentonite session on July 9th with a talk about boron and boron isotopes in smectites from bentonite deposits. Despite a slight fear of public presentations it went absolutely fantastic and I received plenty of good feedback from scientists coming from Italy, Germany, Greece, the UK, the US, and many others. It was great to hear positive but honest feedback. I really enjoyed the comments that specifically addressed what the audience really liked. The meeting was also well organised and the conference dinner location was excellent.

Some impressions:
Our latest results...

...me summing-up what we now know.

Edinburgh castle.

Salisbury Crags.

Centre of Edinburgh.