Mineralogy of Aggregates and its affect on Durability:
The mineralogy of the aggregate is, of course, the function of the rock type. The main rock types in use as aggregates are:
Igneous minerals such as quartz, feldspar, and ferromagnesians - olivine, pyroxene, amphibole, and mica are found in granite, granite gneiss, gabbro, diorite, basalt, diabase (trap rock), andesite, rhyolite, etc. All of them are silicate, and some may present durability problems.
Metamorphic minerals are more varied, depending on the original rock that was metamorphosed. The igneous rocks produce silicate minerals in granite gneiss, and granulite, and are similar to those above, with the exception of olivine and pyroxene. Shale produce slates containing mostly sericite and mica; carbonates produce marbles with calcite and dolomite as the principal minerals.
Sedimentary minerals are either derived from existing rocks, or precipitated from seawater. Quartz and mica silicate particles are found in sandstones and siltstones, and clay particles in shale. Calcite and dolomite predominate in limestone and dolostone, although they may also contain some of the silicate particles.
