Corian is a man-made material, while granite is a naturally occurring stone. Geology.com describes the formation of granite as a slow crystallization of magma within the Earth. The site also goes on to explain that granite is made mostly of quartz and feldspar with small quantities of amphiboles, mica and various other minerals. Reference.com notes that Corian is made of alumina trihydrate and acrylic polymer and is manufactured by DuPont.
About.com compares granite and Corian for use on countertops and finds that both have advantages and disadvantages. In the area of cost, they find installing a high-grade Corian countertop is approximately the same as installing low-end granite. They also find Corian offers greater durability and less maintenance, as granite requires sealing and is subject to cracking. In addition, homeowners can buff minor scratches and dents from the man-made material. In the area of ease of installation, their review finds DuPont's product to offer greater flexibility than granite does.
When it is time to resell the home, granite slab countertops offer the highest return on the dollar, followed by granite tiles. However, the About.com review found that of all the man-made materials available, Corian offers the best consumer name recognition and a good return of one's investment.