Biotite/Muscovite Preparation for Step Heating Analysis
The department is equipped with mineral separation facilities. We can process your sample if it cannot be done at your facility. Just be aware that there is a fee for this work (see Fees). Some general guidelines are given here regarding sample processing and treatment, size fractions needed, and amount of material needed for 40Ar/39Ar analysis; please feel free to contact us for more detailed information prior to sending your samples.

NOTE: The ideal sample is as coarse in grain size as possible. After irradiation very fine grained separates become radioactive powder and present serious concerns for contamination in the lab.

The general rule is that the coarsest size fraction which can be separated from your rock without composite (multi-mineralic) grains is desirable. Coarse material is easier to handle and less dangerous after it has been irradiated. Pure mineral separates are critical. Coarse-grained samples may often be most easily separated by hand picking under a binocular microscope. Samples separated using heavy liquids such as bromoform must be rinsed thoroughly in acetone afterwards to avoid potential contamination of our vacuum system. Zapping the mineral separates in acetone followed by distilled water in an ultrasonic bath will aid in final cleanup also. We need approximately 50-100 mg of a typical mineral separate for analysis. Biotite (~3.0-3.1 G) may be settled out of your heavy liquid and removed by using a S.G. of ~3.10, this will leave muscovite and other lighter minerals floating. Muscovite (~2.8-3.0 G) can then be settled out by reducing the G of your heavy liquid to ~3.0, this will basically leave quartz and feldspars floating. Note that if you have a rock with only biotite or muscovite in it they can sometimes be separated easily by the "paper shaking" technique. Micas will be in the size range 200-500 Ám in many rocks.