Sand gravitation of desert might give Sahara tropical reason. Photovapor of silica is an analogy of Photoelectron. If incindence angle of photon on the surface of water is very oblique, photovapor of dangling bond silica molecules might have antiparallel spin normal to the incidence plane.
Measured by mass, silicon makes up 25.7% of the Earth's crust and is the second most abundant element in the crust, after oxygen. Pure silicon crystals are very rarely found in nature; they can be found as inclusions with gold and in volcanic exhalations. Silicon is usually found in the form of silicon dioxide (also known as quartz), and other more complex silicate minerals.
Silica occurs in minerals consisting of (practically) pure silicon dioxide in different crystalline forms. Amethyst, agate, quartz, rock crystal, chalcedony, flint, jasper, and opal are some of the forms in which silicon dioxide appears. Biogenic silica occurs in the form of diatoms, radiolaria and siliceous sponges.
Silicon also occurs as silicate minerals (various minerals containing silicon, oxygen and one or another metal), for example the feldspar group. These minerals occur in clay, sand and various types of rock such as granite and sandstone. Feldspar, pyroxene, amphibole, and mica are a few of the many common silicate mineral groups.