Acoustic microscopy of rocks

Abstract

SUMMARY Acoustic images of two common rocks, granodiorite and limestone, are studied to explore the kind of geological information that they can provide. The contrast is primarily due to Rayleigh waves; in rock specimens they are mainly affected in their propagation by crystal anisotropy and surface discontinuities. Therefore, acoustic microscopy makes possible detailed identification of intragranular structures in the rock‐forming minerals (very fine cracks, grain and subgrain boundaries, etc.); these features may appear more sharply than in transmitted polarized light microscopy or in scanning electron microscopy. In particular the acoustic images are effective in microfractographic studies, they can show not only the finest cracks, even those much less than a wavelength wide, but also their position in relation to the grain and subgrain structure.