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Other types with dark bands or mottling in gray, green, or yellow are also known.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.Obsidian has a glassy lustre and is slightly harder than window glass.
Many samples of obsidian contain spherical clusters of radially arranged, needlelike crystals called spherulites.This article is within the scope of Wiki Project Time, a collaborative effort to improve the coverage of Time on Wikipedia.This article is within the scope of Wiki Project Archaeology, a collaborative effort to improve the coverage of Archaeology on Wikipedia.Microlites (tiny polarizing crystals) of feldspar and phenocrysts (large, well-formed crystals) of quartz may also be present.
Most obsidian is associated with volcanic rocks and forms the upper portion of rhyolitic lava flows.Many religious folk are opposed to the use of this kind of dating. How acurate is this kind of dating and how do we know this happens over the time frames suggested?