Amorphous and Crystalline Solids as Artifacts in SEM Images
Minerals can precipitate in samples after coring and after preparation for scanning electron microscope (SEM) imaging. Re-deposition of solids from ion milling also produces artifacts that can be observed in images. Both mineral precipitates and re-deposited solid mixtures can be obvious artifacts, but they can also be subtle and challenging to interpret as features that are not present in the subsurface. The most common mineral precipitates are hydrous calcium sulfate (gypsum or bassanite) and halite. Iron sulfate minerals are also commonly observed. These types of artifacts are illustrated, with examples from ion-milled, mechanically polished, and freshly broken surfaces of various sedimentary rocks. Recognition of these artifacts is important because they can reduce porosity and pore size in SEM images and can affect measurements of rock composition and interpretations of pore fluid chemistry.