Deuterium (D)-rich interplanetary dust particles (IDPs) are the most primitive extraterrestrial materials available for laboratory studies in terms of their mineralogy, chemistry, and isotopic compositions. Transmission electron microscopy analysis of one such D-rich IDP shows it to be a highly porous object that consists of crystalline grains (Mg-rich pyroxene and olivine, and FeNi sulfides) and glass with embedded metal and sulfides (GEMS) enclosed within a matrix of amorphous carbonaceous material. The nonsolar H isotopic anomaly measured in this IDP provides direct evidence for the incorporation of partially preserved cold molecular cloud material that predates the solar system. These results indicate that organic molecules associated with the carbonaceous matrix of the IDP are the most likely D carrier phase in the particle. GEMS are a major constituent of this D-rich IDP. The physical and chemical characteristics of GEMS show many similarities to the properties of interstellar amorphous silicates inferred from astronomical observations including: size (diameters of 0.1--0.5 um), solar abundances for heavy elements, presence of superparamagnetic FeNi metal, and an amorphous silicate matrix. Infrared transmission spectra from GEMS-rich IDPs show marked similarities to astronomical data for interstellar silicates. The close association of GEMS and mineral grains to D-rich matter of probable interstellar origin suggests that these inorganic materials are themselves interstellar grains. ¿ 2000 American Geophysical Union