The mineral composition, i.e. the representation of crystals of different atomic constituents and strength, is of certain importance to the engineer. Geologists often claim that it is necessary for the engineer to be able to recognize all the individual minerals of a rock, but true need for this is usually only for five particular purposes, namely:

1. For estimating the wearing of driilbits (richness in quartz)
2. For structural characterization of rock material with respect to presence of zones of weak minerals (mica, chlorite bands)
3. For judging the sensitivity of a rock to chemical degradation by heat or dissolution (sulphates, chlorides, feldspars), or to mechanical degradation at compaction of rockfill (richness in mica)
4. For identification of weathering that causes slaking or expansion on exposure to water (clay minerals)
5. For estimating the mechanical properties of discontinuities that are commonly coated or filled with minerals with special properties (chlorite, graphite and clay minerals)

Reference:

R. Pusch, Rock Mechanics on a Geological Base: Elsevier Science, 1995.