The ability to quantify lithium by EPMA became a reality in 2008. The concentrations of elements from lithium to plutonium may be measured at levels as low as 100 parts per million (ppm), material dependent, although with care, levels below 10 ppm are possible. This enables the abundances of elements present within small sample volumes (typically 10-30 cubic micrometers or less) to be determined, when a conventional accelerating voltage of 15-20 kV is used. It works similarly to a scanning electron microscope: the sample is bombarded with an electron beam, emitting x-rays at wavelengths characteristic to the elements being analyzed. This model is housed at the Cambridge Museum of TechnologyĪn electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. A Cambridge Scientific Instrument Company "Microscan" electron probe microanalyzer based on a design by Peter Duncumb. ↑ "A comparison of obsidian and surgical steel scalpe.The Western Journal of Medicine, 136, 265-269 Ancient technology in contemporary surgery. ↑ Obsidian was also used on Rapa Nui ( Easter island) for edged tools such as Mataia and the pupils of the eyes of their Moai (statues).↑ "Perlite - Mineral Deposit Profiles, B.C.Primitive Technology: A Book of Earth Skills. ↑ Obsidian is found in rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid.Obsidian can also be found in Armenia, Turkey, Italy, Mexico, Iceland, Greece and Scotland. Deposits can be found in many other western US states including Arizona, Colorado, Texas, Utah, Oregon and Idaho. Yellowstone National Park has a mountainside containing obsidian between Mammoth Hot Springs and the Norris Geyser Basin. There are solid obsidian flows in the calderas of Newberry Volcano and Medicine Lake Volcano in the Cascade Range of western North America, and at Inyo Craters east of the Sierra Nevada, California. Obsidian can be found where high silicate eruptions have happened. Modern archaeologists have developed a dating system to calculate the age of obsidian artifacts depending from the content of water in the object. Obsidian cores (unworked lumps) and blades were traded great distances inland from the coast. Obsidian can be identified in Greece as coming from different islands in the Aegean Sea. So archaeologists can trace the origins of a particular artifact. Each volcano and in some cases each volcanic eruption produces a distinguishable type of obsidian. Native American people traded obsidian throughout North America. Called a macuahuitl, the weapon could cause terrible injuries, because it combined the sharp cutting edge of an obsidian blade with the ragged cut of a serrated edge. Mesoamericans also made a type of sword with obsidian blades mounted in a wooden body. It was also polished to create early mirrors. It was worked for tools and decorative objects. Pre-Columbian Mesoamericans' used obsidian often. Obsidian was valued in Stone Age cultures because, like flint, it could be chipped to produce hand axes, sharp blades or arrowheads. It may contain patterns of gas which produce effects such as a golden sheen ( sheen obsidian) or a rainbow sheen ( rainbow obsidian). In some stones, small crystals produce a snowflake pattern ( snowflake obsidian). Iron and magnesium typically give the obsidian a dark green to brown to black color. Usually dark, the color varies on the presence of different materials. Obsidian has little water, but takes it in if it sits in groundwater. It breaks down faster when water is present. So, no obsidian is older than Cretaceous age. Over time, the glass becomes fine-grained crystals. It is metastable: it changes very slowly. It consists mainly of SiO 2 ( silicon dioxide), usually 70% or more. Obsidian is mineral-like, but not crystalline.
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