Rocks are naturally occurring solids which are composed of minerals & have been used by humans since ages. From Stone Age, rocks are used for various purposes. Also, the metals and minerals found in rock play an important role in our life. Get to know all the Pseudotachylite Uses. We have provided you with all information about Pseudotachylite rock here. Very fine grained fault rock which is composed of glassy matrix that often contains inclusions of wall-rock fragments.. Pseudotachylite is available in black, brown, colourless, green, grey, pink, white colors. The streak of a rock is the color of powder produced when it is dragged across an unweathered surface. The streak of Pseudotachylite is light to dark brown. Get to know more about Pseudotachylite rock and characteristics of Pseudotachylite rock in the next sections.