**4.2 Ground mass description**

General term from the fine-grained, not discernible part of a rock. In igneous rocks, this is the part of the rock that is not phenocrysts, and can help in determining the composition of extrusive rocks. In sedimentary rocks, it typically refers to the fine-grained components, namely mud. In metamorphic rocks, it is usually referring to material between porphyroblasts or a low-grade rock with only microscopic mineralization [17].

A matrix or ground mass of rock is the mass of fine-grained substantial into which grains, crystals, or large holes are incorporated.

The matrix of igneous rocks contains of fine-grained, usually microscopic, crystals in which bigger crystals are fused. This porphyry tissue is revealing that magma was cooled in multi stages.

A sedimentary rock matrix is a fine-grained sedimentary material, such as clay or silt, in which larger grains or lumps are incorporated. It is also used to describe the rock material in which the fossil is included [7, 17].
