What is an aggregate in mineralogy ?
Crystalline aggregate
This term designates an assembly formed of numerous crystals (automorphic to xenomorphic) of the same or different nature, thus constituting a rock. Lapis lazuli (photo below) is an aggregate of lazurite, calcite and pyrite. If the crystals are all of the same mineral species, then we speak of monomineral rock (such as quartzite, which consists only of quartz).