Carbonaceous chondritic matrix material (CCMM) appears to be an important planet-forming unit in the mid-solar system, from the orbit of Mars to that of Uranus. The type specimen for CCMM is the lowtemperature (400-500 K) assemblage of clay minerals, organic polymer, magnetite, and Ni-rich iron sulfides which constitutes the black, fine-grained matrix of primitive carbonaceous chondrites. Solar-system objects which appear to be partly or wholly made of CCMM are the satellites of Mars, most asteroids, interplanetary dust, and, perhaps, comets, satellites of the outer planets and the rings of Uranus. CCMM constituents probably formed by low-temperature reactions of higher-temperature condensates with the ambient solar composition gas, or in the case of the organic polymer, by reactions of gaseous species catalyzed by solids.
Carbon is the fourth most abundant element. Its mode of occurrence in the solar system is quite varied; it is found in molecules that occur naturally in atmospheres, oceans, ices, living organisms, rocks and metal alloys. This paper is concerned solely with solid "carbonaceous material" in which the element carbon itself may constitute only a few weight percent of the matter. Nevertheless, the carbonaceous material possesses certain other characteristics in addition to the presence of solid carbon compounds which distinguish it as an unique planet-forming rock unit. Carbonaceous material is recognized as important because of its apparent wide distribution in the solar system and because it is a relatively primitive material. Before proceeding further, it is essential to characterize this "carbonaceous material" so that the distinctions from other carbon-bearing matter are clear. The type-specimens for the carbonaceous material are the carbonaceous chondritic meteorites, in particular the fine-grained matrix in CM ~ carbonaceous chondrites.