Lightweight, steady and stiff mirrors are necessary to decrease cost of telescopes such as IXO and GenX used in special NASA missions. Low-density materials are ideal for use as mirrors in such applications. Beryllium has been traditionally considered ideal for lightweight mirrors requiring high rigidity. The toxicity of beryllium poses a major problem. Polished Silicon Carbide (SiC), prepared by Chemical Vapor Deposition (CVD), is the current material of choice for fabrication of mirrors in lightweight telescopes. However, CVD is a complex and expensive technique and the quality of SiC produced is very sensitive to the processing conditions. MMI proposes to utilize a novel displacement reaction to obtain fully dense B4C based composite mirrors with unique microstructural features. Phase I will involve preparing the lightweight optical mirror material and evaluating their mechanical, thermal and optical properties. Phase II will involve optimization of the processing, consolidation and polishing procedures for the composite. In collaboration with industrial partners, who manufacture special purpose optics, mirrors will be fabricated and tested in Phase II for use in various applications.