NOVELTY - A silicon-containing particulate material is formed by reducing particulate starting material which has silica-containing particles having aspect ratio of greater than or equal to 3:1 and smallest dimension of less than or equal to 15 mu m or reducing particulate starting material which has silica-containing particles consisting of elongate structural elements each having aspect ratio of greater than or equal to 3:1 and smallest dimension of less than or equal to 15 mu m.    USE - Formation of silicon-containing particulate material for electrode and slurry used for rechargeable metal ion battery (all claimed), such as lithium ion batteries, electrochemical cells, lithium air batteries, flow cell batteries, fuel cells, and thermal batteries, photovoltaic devices e.g. solar cells, filters, sensors, electrical and thermal capacitors, microfluidic devices, gas/vapor sensors, thermal or dielectric insulating devices, devices for controlling or modifying transmission, absorption, or reflectance of light or other forms of electromagnetic radiation, chromatography, and wound dressings.    ADVANTAGE - The desired structured silicon shape can be obtained with reduced or no waste of starting material, process is low cost, and performance of rechargeable metal ion battery is improved.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) electrode containing active material of silicon-containing particulate material;    (2) slurry containing silicon-containing particulate material and greater than or equal to 1 solvent;    (3) formation of electrode which involves depositing slurry on conductive current collector and evaporating solvent; and    (4) rechargeable metal ion battery containing anode which has electrode capable of inserting and releasing metal ions, cathode formed from metal-containing compound capable of releasing and reabsorbing metal ions, and electrolyte between anode and cathode.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of the process for forming silicon-containing particulate material.    Process of obtaining silica from silica source (101)    Modification of silica (103)    Reduction of silica to form silicon (105)    Silicon treatment (107)