Top Customer Reviews. Failure of an off-side windshield wiper blade resulted in an arc of light scratches on the glass of my concours-winning collector car. Ranging from almost-undetectable to 'can just feel them under my fingernail' the scratches caught the light and weren't going to pass muster at my next car show.
An obsidian rock is an extrusive igneous rock that forms when a volcano erupts and has no time to crystallize, so it has a glassy texture. Obsidian rocks are generally black i â¦ n color.o rock is completely impermeable, but some porous rocks like shale and pumice are mostly impermeable, because â¦ the pores are not interconnected, thus not allowing fluids or gases to pass through them. This is why shale makes a good cap-rock, and pumice floats instead of sinking. 2 people found this useful.
Obsidian may also be red-brown due to the presence of iron, and greenish or grey due to the presence of tiny gas bubbles. It has a massive structure, with, in some cases, the presence of latent concentric fractures (perlitic fractures). Obsidian is derived from the rapid cooling of a viscous, granitic magma.