Black Obsidian Gemstone Roller Face Massager Guasha for Facial Massage Manufacturer supplier Exporter Wholesaler from Jaipur, Rajasthan, India Obsidian has a glassy lustre and is slightly harder than window glass. Though obsidian is typically jet-black in color, the presence of hematite (iron oxide) produces red and brown varieties, and the inclusion of tiny gas bubbles may create a golden sheen. Other types with dark bands or mottling in gray, green, or yellow are also known. Obsidian generally contains less than 1 percent water by weight. Under high pressure at depth, rhyolitic lavas may contain up to 10 percent water, which helps to keep them fluid even at a low temperature. Eruption to the surface, where pressure is low, permits rapid escape of this volatile water and increases the viscosity of the melt. Increased viscosity impedes crystallization, and the lava solidifies as a glass.