Preparation of oriented cube samples for AMS

Preparing oriented cubes for anisotropy of magnetic susceptibility (AMS) testing is relatively easy after preparing oriented slabs for thin sections. In most cases the "scrap" from slab cuts provided enough material to make the 20mm cubes with very little effort. Preparing cubes is much easier than slabs because they are smaller and may come from any part of the rock.

The technique is as follows. The cubes must be cut so that one set of faces is parallel to bedding, another parallel to strike, and the last in the dip plane. This is easiest to accomplish by taking a scrap slab that is already orientated as PTB, PTS, or IDP and measuring out cuts to produce cubes. Before any cuts are made a sketch was made in the log book and the space where each cube would be cut out was labeled to prevent the loss of orientation.

AMS Cubes

Each cube was labeled on three sides as shown above. The sample name and strike/dip symbol were labeled on the PTB face, the stratigraphic up and down dip directions on the IDP face, and the stratigraphic up and sample number on the PTS face. Redundancy was necessary in case the cubes needed to be trimmed down at test time to fit in the sample holder or to remove metal filings left by the saw.

The preferred number of cubes for test validity was 6, with a bare minimum of 4. Approximately 4-10 cubes were produced for each sample.