Iron thermite uses aluminum powder and iron oxide, but silicon thermite needs an additional ingredient besides silicon dioxide to be successful. Adding sulfur creates more heat in a side reaction with aluminum, thus helping the reaction keep going. I used a 12:10:9 mass ratio of S:SiO2:Al. All the materials were finely powdered, and the silicon dioxide came as 400 mesh chromatography media from some company online. They had a free samples program, so I readily agreed to get free chemicals!
After mixing the ingredients, I placed them in a flowerpot and lit them with a magnesium ribbon fuse. The reaction was extremely bright and wonderful, but I'll let the video speak for itself:
When the reaction had cooled, I put the slag pieces in water and hydrolyzed off all the aluminum sulfide. I then sifted the silicon beads out from the resulting aluminum oxide powder. I may have lost some, but I still got a decent number of small beads of silicon. They weren't very shiny, so I soaked them in dilute hydrochloric acid for an hour or so until I could see the pretty crystals inside. They turned out quite nicely, and I was happy to isolate another element in my backyard!