I am working on a XRD of a carbonate sediment and there is a d=4.85A peak that matches very good to gibbsite. However I believe it is quite unusual to have gibbsite in a muddy limestone. What do you recommend me?
Dear Mrs. Silveira,
It is not uncommon, because limestone with different amounts of non-calcareous impurities is the most widespread host rock of karst bauxite. It is a clear indication that there is a strong supergene alteration under a tropical climatic regime affecting the calcareous rocks. Try and isolate the impurities from the carbonate matrix and investigate them in detail so you will get an idea what the supergene alteration affecting the limestone looked like. There may be further minerals such as kaolinite, anatase.. Monochloroacetic acid is milder than hydrochloric acid and spares some of the impurities and I am sure your will get a good separate of minerals amenable to XRD and SEM-EDX/WDX
With kind regards H.G.Dill
Thanks Prof Hill! That´s a good ideia to isolate impurities before XRD analysis.
Hi Armel, thanks for the answer! It is really nice to find people so far way and with research interests so close. I was just wondering how in a carbonate environment it is possible to cristalize gibbsite... I am used with gibbsite in weathered soils due to high lixiviation. And I believe a muddy limestone cristalizes in a very enriched environment. So how both geochemical conditions match?
It depends on the impurities which in so-called impure limestones may make up as much as 50 % (see Leighton and Pendexter, 1962 ) It is mainly, the clay minerals (e.g,. illite, smectite, sepiolite, glauconite...) and alkaline feldspar that source these Al oxide-hydrates.
Thanks prof Hill! Very interesting. Leighton and Pendexter, 1962 proposed a carbonate rock classification. I believe it is published in American Association of Petroleum Geologists and unfortunately I don´t have acess.
I was wondering if gibbsite commes as sediment or it is in situ cristalized in a limestone. So according to Leighton and Pendexter, 1962 it is a in situ growth
- Badges
- Science topic
- Similar topics
- Geoscience
- Cartography
- Mapping
- Maps