Matrix (geology)

From Freepedia

The matrix or groundmass of an igneous rock consists of fine grained often microscopic crystals in which larger crystals (phenocrysts) are embedded. This porphyritic texture is indicative of multi-stage cooling of the magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix. Also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock (kimberlite) called "yellow ground."

In sedimentary rocks, matrix refers to a fine grained clay or silt in which larger fragments are embedded.