SIMS applications to microscopic grains. In January 2020, analysis of the Murchison meteorite found in Australia in 1969 revealed that its stardust formed 5 to 7 billion years ago, older than Earth's 4.6 billion year-old sun, making the meteor and its stardust the oldest solid material ever discovered on Earth. In meteorites Presolar grains are the solid matter that was contained in the interstellar gas before the Sun formed. The stardust component can be identified in the laboratory by their abnormal isotopic abundances and consists of refractory minerals which survived the collapse of the solar nebula and the subsequent formation of planetesimals. To meteorite researchers, the term presolar grains has come to mean presolar grains found in meteorites, which consist overwhelmingly of stardust. Many other types of cosmic dust have not been detected in meteorites. Presolar stardust grains comprise only about 0.1 percent of the total mass of particulate matter found in meteorites. Such grains are isotopically-distinct material found in the fine-grained matrix of meteorites, such as primitive chondrites. Their isotopic differences from the encasing meteorite require that they predate the Solar System. The crystallinity of those clusters ranges from micrometer-sized silicon carbide crystals (up to 1013 atoms), down to that of nanometer-sized diamond (about 1000 atoms), and unlayered graphene crystals of fewer than 100 atoms. The refractory grains achieved their mineral structures by condensing thermally within the slowly cooling expanding gases of supernovae and of red giant stars. Characterization Presolar grains are investigated using scanning or transmission electron microscopes (SEM/TEM), and mass spectrometric methods (noble gas mass spectrometry, resonance ionization mass spectrometry (RIMS), secondary ion mass spectrometry (SIMS, NanoSIMS)). Presolar grains that consist of diamonds are only a few nanometers in size and are, therefore, called nanodiamonds. Because of their small size, nanodiamonds are hard to investigate and, although they are among the first presolar grains discovered, relatively little is known about them. The typical sizes of other presolar grains are in the range of micrometers. Presolar grains consisting of the following minerals have so far been identified: diamond (C) nanometer-sized grains (~ diameter) possibly formed by vapor deposition graphite (C) particles and anions, some with unlayered graphene cores silicon carbide (SiC) submicrometer to micrometer sized grains. Presolar SiC occurs as single-polytype grains or polytype intergrowths. The atomic structures observed contain the two lowest order polytypes: hexagonal 2H and cubic 3C (with varying degrees of stacking fault disorder) as