Here is an insightful video shared by Marvel Stone in Australia showing the Breton method for manufacturing quartz surfacing (also known as engineered stone). The finished slabs are becoming more and more popular (and trendy) for countertop fabrication. Quartz surfacing is one of the most quickly growing countertop materials in the United States.
From what I know each new Breton quartz line is a little different from previous versions because of refinements, but they are all very similar and this is the most well-known process for manufacturing quartz surfacings. Most, if not all, of the major brands – Silestone, Cambria, Zodiaq, Caesarstone, Radianz, Viatera, Hanstone, etc. – use the patented Breton System.
Nowadays there are other methods (and knock-off methods) being used, but this is basically the standard.