Matrix
Matrix is the fine-grained material that fills the spaces between the larger grains in a meteorite, like the cement between pebbles.
Look closely at a chondrite and you will see bigger objects, such as chondrules and metal flecks, sitting in a background of much finer material. That background is the matrix. It is made of dust-sized grains, many only a few micrometres (thousandths of a millimetre) across, of minerals such as olivine and pyroxene, along with sulfides and, in some meteorites, clays and carbon-rich compounds.
The matrix matters because it is a sample of the dust that floated in the early Solar System. In the most primitive meteorites it can hold rare grains older than the Sun and organic molecules. How much matrix there is varies a lot. In ordinary chondrites it is a modest part of the rock, while in CM chondrites such as Murchison, which fell in Australia in 1969, matrix makes up most of the meteorite. In CI chondrites there are almost no chondrules, so the rock is nearly all matrix.
On a cut face, the matrix is the darker or finer-looking material between chondrules. In meteorites that were heated strongly inside their parent asteroid, the matrix recrystallises and becomes harder to tell apart from the chondrules.
Related terms
Level: Explorer Ages 10 and up