Know all about Greywacke and Obsidian properties here. All properties of rocks are important as they define the type of rock and its application. Greywacke belongs to Sedimentary Rocks while Obsidian belongs to Igneous Rocks.Texture of Greywacke is Clastic whereas that of Obsidian is Glassy. Greywacke appears Dull and Obsidian appears Shiny. The luster of Greywacke is dull while that of Obsidian is vitreous. Greywacke is available in beige, black, brown, colourless, cream, dark brown, green, grey, light green, light to dark grey, pink, red, white, yellow colors whereas Obsidian is available in black, blue, brown, green, orange, red, tan, yellow colors. The commercial uses of Greywacke are as armour rock for sea walls, petroleum reservoirs, sea defence, tombstones and that of Obsidian are creating artwork, mirror, used in aquariums.