Mortars are common and essential elements of masonry historical buildings and are composed by a binder, aggregates and eventually, some additives. The binder provides consistency to this composite material, and until the emergence of Portland cement in the 19th century, lime was the main binder used. The aggregates are normally sand or rock fragments with variable sizes. The whole set is morphologically very similar to a sedimentary clastic rock with carbonate cementing. Following an old tradition of microscope use in this kind of rocks, it is not surprising the application of optical microscopy to mortars as also happened with concrete.