Orgon orgon rock dating method
Obsidian-bearing volcanoes are typically located in or near areas of crustal instability or mountain building.In North America, obsidian is found only in localized areas of the West, where the processes of plate tectonics have created geologic conditions favorable to volcanism and the If obsidian is similar in composition to granite and rhyolite, both of which were originally molten, then why is obsidian glassy?The answer relates to the original cooling rate and water content of the magma.Granite cools very slowly miles below the surface of the earth; this slow cooling over millions of years allows for the formation of sizable mineral crystals within the slowly cooling mass of molten rock.This had obvious advantages for our Stone Age ancestors, who used obsidian extensively for tool making. Because obsidian is not comprised of mineral crystals, technically obsidian is not a true "rock." It is really a congealed liquid with minor amounts of microscopic mineral crystals and rock impurities.
When rhyolite magma approaches the earth's surface and the pressure of burial decreases, most of the water in the magma is lost as steam.Clear varieties of obsidian contain very few opaque impurities or microscopic mineral crystals.Red or brown obsidian generally results from tiny crystals or inclusions of hematite or limonite (iron oxide).Abundant, microscopic crystals of minerals like magnetite, hornblende, pyroxene, plagioclase and biotite, combined with tiny fragments of rock, likely produce the jet-black varieties of obsidian.Microscopic crystals of various types of feldspars may yield the unique blue, green, purple or bronze colors associated with rainbow obsidian.
This smooth, curved type of fracture surface occurs because of the near-absence of mineral crystals in the glass.