TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Parameters: Aspect ratio of silica-containing particles or elongate structural elements is greater than or equal to 5:1. Smallest dimension of silica-containing particles or elongate structural elements is less than or equal to 10 mu m, preferably less than or equal to 3 mu m. The geometric surface area of silicon-containing material is the same as or greater than the geometric surface area of starting material. The shape of the particles of silicon-containing material is the same as the shape of starting material particles. The starting material has an enclosed void volume, and the smallest dimension is a thickness of a wall of starting material enclosing the void volume. The smallest dimension of starting material is an external thickness of the starting material. Silicon-containing material has Brunauer-Emmett-Teller (BET) value which is the same as or less than the BET value of starting material. Silicon-containing material has BET value of less than or equal to 100 m2/g, preferably less than or equal to 50 m2/g. Preferred Processes: All silica of starting material is reduced. Silica on the surface of starting material particles is reduced, and silica at the core of starting material particles is not reduced. Silica at the core is selectively removed by exposure to hydrofluoric acid (HF). Starting material is reduced at less than or equal to 750 degrees C, preferably less than or equal to 650 degrees C. Starting material is reduced by exposure to liquid metal or metal vapor. Reduction is performed in the presence of thermal moderator, preferably a salt, which is mixed with starting material and reducing agent. A layer of thermal moderator is in contact with starting material. Silica is reduced by exposure to a reducing composition that causes both reduction of silica and doping of silicon. A part of the surface of silicon-containing material is coated with silicon oxide or carbon. Starting material is formed by electrospinning silica on a patterned collector defining a shape for starting material. Only silica is electrospun. Silicon-containing particulate material is treated to remove reaction by-products by hydrochloric acid (HCl) treatment. Silicon-containing particulate material is etched to form silicon pillars extending from silicon core of particulate material. Silicon-containing material is etched by metal-assisted chemical etching. Preferred Compositions: Silicon-containing particulate material formed after selective removal of silica is a flake having a hollow core or a tube. Starting material is n- or p-doped or undoped. Starting material particles have an open framework structure. Metal is magnesium or calcium. Starting material is a biogenic silica. Starting material contains less than or equal to 95 wt.%, preferably less than or equal to 90 wt.% silica. Metal ion battery is lithium ion battery. Particulate starting material contains amorphous or nanocrystalline silica, and silicon-containing particulate material contains microcrystalline or nanocrystalline silicon. Particulate starting material contains silica with softening temperature lower than reaction temperature at which starting material is reduced.