Baddelyite and its counterpart zircon are both insoluble in HF. Mixing it with aqua regia (HNO3+HCL = 1:3) is the "hardest stuff" in terms of solution and you crack a wide range of silicates and oxides and hence you cannot predict how much has been added to your solution from minerals associated or intergrown with baddeylite. When I was with geochronology branch we always tried to avoid solution processes as a preparatory method and rather used the handpicking if possible.

HGD

For geochronology, I agree with H.G. Dill to avoid solution processes whenever possible. You already have a fine to coarse powder that you can use with heavy liquid separation, clean up with acetone and hand pick the crystals after that. The main problem with acids is that you are dealing with undiuted version that have many drawbacks such as vapors, spill-over droplets, very strong reactions with powdered rocks and the non-least one, a higher health risk to the operator. These acids will eat through clothes and skin rapidly and one can end up in hospital for treatment if a pure HF droplet or vapor gets under the skin; it attacks the nerves and is extremely painful.

As for the effects of this rock powder dissolution method on the geochronology results, the problems can be many folds. Cracks in baddaleyite crystals can fill up with dirty acid filled with U and Pb from the dissolved minerals and a very thin (1-2 microns) layer of the surface can have partial leaching and/or contamination. This leaching can be offset by abrading the grains as with zircons in case of chemical geochronological analysis. The problem with using commercial grade is that you have no control on the amount of 204Pb you 'add' to the system through cracks and surface porosity. One mistake is to start with the assumption that baddeleyites are 'impermeable', which is not really the case. They have the same problems as zircons have.

The important thing is with which machine type you are measuring the isotopes, a 'classical' mass spectrometer from chemical dissolution and separation analysis or an ICPMS directly on polished grains?

Overall, the problem of baddaleyite separation and analysis are the same as with zircon, in both case the U and Pb are not that strongly attached to the crystal lattice, only the mineral lattice itself is strong enough to trap quite efficiently U and Pb. The best advice is to take the same precautions that one would use for zircon extraction and it should go well.

Thanks Francine and Harald for the responses. The aim is to date the baddeleyite grains by spot analysis (Ion probe or LA-ICPMS). The safety issue aside, can the spot analysis approach avoid the grain rocms and cracks filled with dirty Pb?

It all depends upon the size of your beam vs the size of the mineral to be able to avoid hitting a crack. The best bet is to use the cleanest grains with ideally no cracks, inclusions or core (happens often with zircon). A gem-quality type of grain gives you way more chances to have genuine results. The old motto "garbage in, garbage out" applies well here, one must control what is analyzed to obtain reliable results. If you work on embedded grains in resin disk that is polished flat, try an electronic microscope imagery (under cathodo-luminescence if possible) to look at the grain surface to help you make the best choice of target within a given grain. With a few MEB photos of your minerals, you can have a better appreciation as to where to put your beam on a given grain.

Thanks Francine.