well as 1-dimensionally disordered SiC grains. In comparison, SiC synthesized in terrestrial laboratories is known to form over a hundred polytypes. titanium carbide (TiC) and other carbides within C and SiC grains silicon nitride () corundum () spinel () hibonite () titanium oxide () silicate minerals (olivine and pyroxene) Information on stellar evolution The study of presolar grains provides information about nucleosynthesis and stellar evolution. Grains bearing the isotopic signature of "r-process" (rapid neutron capture) and alpha process (alpha capture) types of nucleosynthesis are useful in testing models of supernova explosions. For example, some presolar grains (supernova grains) have very large excesses of calcium-44, a stable isotope of calcium which normally composes only 2% of the calcium abundance. The calcium in some presolar grains is composed primarily of 44Ca, which is presumably the remains of the extinct radionuclide titanium-44, a titanium isotope which is formed in abundance in Type II supernovae such as SN 1987A after rapid capture of four alpha particles by 28Si, after the process of silicon burning normally begins, and prior to the supernova explosion. However, 44Ti has a half-life of only 59 years, and thus it is soon converted entirely to 44Ca. Excesses of the decay products of the longer-lived, but extinct, nuclides calcium-41 (half-life 99,400 years) and aluminium-26 (730,000 years) have also been detected in such grains. The rapid-process isotopic anomalies of these grains include relative excesses of nitrogen-15 and oxygen-18 relative to Solar System abundances, as well as excesses of the neutron-rich stable nuclides 42Ca and 49Ti. Other presolar grains (AGB star grains) provide isotopic and physical information on asymptotic giant branch stars, which have manufactured the largest portion of the refractory elements lighter than iron in the galaxy. Because the elements in these particles were made at different times (and places) in the early Milky Way, the set of collected particles further provides insight into galactic evolution prior to the formation of the Solar System. In addition to providing information on nucleosynthesis of the grain's elements, solid grains provide information on the physico-chemical conditions under which they condensed, and on events subsequent to their formation. For example, consider red giants — which produce much of the carbon in our galaxy. Their atmospheres are cool enough for condensation processes to take place, resulting in the precipitation of solid particles (i.e., multiple atom agglomerations of elements such as carbon) in their atmosphere. This is unlike