Blastomylonites are coarse grained, often sugary in appearance without distinct tectonic banding. Ultramylonites usually have undergone extreme grainsize reduction. In structural geology, ultramylonite is a kind of mylonite defined by modal percentage of matrix grains more than 90%.[1] Ultramylonite is often hard, dark, cherty to flinty in appearance and sometimes resemble pseudotachylite and obsidian.