Stress-induced Magnetic Anisotropy of Rocks

Abstract

ROCKS containing 1 or 2 per cent of magnetic minerals are so slightly ferromagnetic that reliable measurements of magnetostriction by the direct observation of changes in dimensions would, at best, be extremely difficult. However, an understanding of the magnetostriction of rocks is very desirable on account of the disagreement which has arisen concerning its possible role in palæomagnetism^1–4. The purpose of this communication is to report an experiment which shows that the saturation magnetostrictions of rocks are easily measured in terms of stress-induced anisotropy, and that, in the few rocks examined, they have values which would be expected from their known magnetic mineral contents.