What Is the Stroma?

The mineral particle size of some rocks is very different. Large particles are scattered among small particles. Geologically, the large mineral particles are called phenocrysts, and the small ones are called matrices. The matrix is a fine-grained debris material and clay minerals smaller than 0.03 mm. They are generally mechanically deposited together with the debris material, and they also act as a cementation for the debris particles. Because their particles are very small, the outline of the particles cannot be clearly seen to the naked eye. Most of them are mud-like structures, with earth-like fractures, dim gloss, and various colors. They are different due to the mixing of different pigment substances.