Overview

The necessity of preparing individual mineral phases out of a hard rock arises from very different questions: E.g. feldspars for Sr isotopes or age dating with the Ar-Ar method, olivines for helium isotopes, separation of altered from fresh ground mass, separation of glass from residual rock, zircons for age dating with the U-Pb method, etc. Depending on the starting material, a sole manual selection under a binocular in order to obtain the necessary quality and quantity of the separates would be very time-consuming. The possibility of enriching the desired mineral or removing undesirable sample components by exploiting its physical properties can save a lot of time. Two methods are used: Density separation and magnetic separator. Both are non-destructive and without sample loss, so that in case of an insufficient separation, the complete sample material is still available for a new attempt.

Density Separation

Density separation works with a heavy liquid made from sodium polytungstate and is adjustable up to a maximum density of 3 g/cm3. The solution is reusable and non-toxic. For a separation, the density of the desired mineral must first be determined using charts. The heavy liquid is then either set with a density greater or smaller. Depending on the desired separation, the sample is placed in the heavy liquid with a defined and pre-set density. After centrifugation two phases are created, a sink fraction and a float fraction. These are separately removed, rinsed and dried.

 

Magnetic Separator

The Frantz LB 1 Magnetic Separator is based on the principle that minerals are variably magnetized depending on their composition and thus behave differently in the magnetic field. Tables from the literature provide an indication on how the magnetic field must be adjusted. By fine-tuning the magnetic field, the steepness and tilting of the sample slide, the separation is optimized and thus an efficient enrichment of the desired mineral achieved.