Where do you find obsidian?
Obsidian is volcanic glass and can be found near active or extinct volcanoes. It is formed when molten silicates (sand) is expelled onto or near the earths surfaces then cools very quickly.
Its dark color is caused by the incorporation of trace elements, such as iron oxide or magnesium oxide into its fabric.
Most of the obsidian used by prehistoric Native American in North America people was quarried from sites in the mountains of western North America (Idaho, Montana, Oregon, Washington, Colorado, New Mexico). However, artifacts made from obsidian sourced to Central and South American lava flows have been found on Mississippian sites (A.D. 1000 - A.D. 1350). Perhaps the most famous of the North American obsidian acquisition areas is Obsidian Bluff in yellow stone park
Is it transparent, translucent, or opaque?
Translucency and opacity depend on a couple of factors: first how thick is the object and second how intense is the light being transmitted. Under normal conditions obsidian is typically translucent or opaque. Rarely is it transparent.
A truly transparent material is clear and contains no intrusions that would significantly disperse, reflect, absorb, and diffuse the transmitted light as it passes through - window glass is a good example.
Translucent materials on the other hand reflect most of the light back to its source while allowing only a portion of the light to pass through.
Opaque materials reflect all light and do not allow any light to pass through. The best way to test translucency/opacity is to take a thin flake of the material and hold it up to the ceiling light. If you can see the light bulb through the material then its transparent, if you can't see the light bulb but the material glows around the edges and at thin spots, then its translucent.
Finally if you can't see any light around the edges or in thin spots then it's opaque.
Is obsidian just black?
No obsidian is not just black. Glass - volcanic glass included - is colored by introducing different elements or compounds. Greens are created by inclusion of phosphate, or copper; reds are created by including gold, oranges and browns by introducing oxidized iron. The black color in obsidian is due to the presence of unoxidized iron and magnesium.
A similar material is produced as a bye-product in the making of iron -- a process called smelting. In this process, iron ore is heated to a temperature that is just below the melting point of iron (1250 degrees Fahrenheit). The iron fuses together while the silicate (sandy) impurities are melt away and drain out of the bottom of the furnace and form a substance called slag.
A smelting furnace replicates a volcano in many ways. I have seen examples of obsidian from Idaho that are black with orange bands and swirls. The color depends on what elements are present - and their amounts, when the obsidian is formed.
How does obsidian come out of the volcano?
The material that forms obsidian can be expelled from a volcanic source is different ways or not at all. Remember, obsidian forms when the material it is made from cools quickly so it needs to be at or near the earth's surface. Obsidian is often found along lava flows, inside vents or dikes, or even in the main shaft.
What was obsidian used for?
When broken, obsidian displays a very sharp edge. Because of its unique cryptocrystalline structure, obsidian, like glass can be broken in a predictable way, but like glass, it is quite brittle and cannot withstand a lot of force. If you shot a B-B from a gun into a pane of glass a small cone would pop out on the opposite side. This would happen every time with the same results if all of the variables are held constant.
Glass, obsidian, chert do not have what is known as cleavage or lines along the crystalline structures where the material is week and break most easily. The force of a blow radiates evenly across the crystalline structure. A diamond has cleavage and it requires great skill to identify and cut it along its cleavage plane. If the cutter strikes it wrong then the diamond turns to dust.
Once prehistoric people became familiar with the properties of these materials, they learned the best ways in which to modify them for their use. Obsidian was transformed into utilitarian tools particularly knives and other cutting tools, but in the hands of a master flintnapper, it could be transformed into beautiful ceremonial objects and objects of art.
How are those items made?
The objects are made by applying the necessary force to the edges of the object. It is very much like whittling a figurine out of a tree branch, but instead of wood you are using stone. It takes a considerable amount of practice to develop the skills necessary to create stone tools and objects.
When did you start making projectile points?
I started my training in flintknapping in 1995. I worked at it daily for about 2 years. I also read a lot of books and articles about the science of flintknapping. By the end of that time I was pretty good at making arrowheads and other stone tools. I no longer do flintnapping
because it changes the musculature in your hands and there are risks of injury. I am a piano player, too, and I enjoy that much more than flintnapping.
What rocks do you use for making projectile points?
You can use just about anything that breaks, holds and edge, and can withstand a certain degree of force when making an arrowhead. However the quality of the end product is going to depend largely on the quality of the material that you are using and the skill of the craftsmen making it. You are also somewhat constrained by what is available to you.
The prehistoric hunters had to use whatever they could find. Sometimes, they would trade to get higher quality material, or they might carry it with them when they went into areas that didn't have material readily available. They might also store, or cache materials at a location if they knew that they would return some day.
The nature of the job to be performed would also dictate what type of material you used. If the job was pounding acorns then you would want a stone that was have, rounded, and not easily broken. If you wanted a chopping tool, you would need a material that was heavy, could be worked into a wedge, and could withstand the force of repeated heavy blows. If you needed an arrowhead, you would prefer working with a material that was light, easily worked, held a sharp edge, and could be hafted to a shaft.
I hope that this answers all of your questions. Thank you for asking. If you have any other questions, you might try finding a book at your school or public library. If not you can always send them along to me.
Dan Higginbottom, Archaeologist
Iowa State Historic Preservation Office |
Mount St. Helens by Tara T.
Mount St. Helens is a very active volcano. From Thornton Creek to Mount St. Helen's it is approximately 200 miles and 3 hours of driving. It had 6 million tiny earthquakes in one day. On May 18, 1980, at 8:00 am, Mount St.Helens erupted. It was the largest volcanic eruption recorded in North American history. Lots of things died (700 wild animals, trees, and humans, 250 homes, 47 bridges). In 2004, Mount St. Helens erupted again and lost 13 more feet of herself.
Johnston Ridge Visitor Center was named after a geologist who studied Mount St. Helens. He was the only one to correctly predict how Mount St. helens was going to erupt and the first one to report the eruption. Johnston made a camp and was taking notes when Mount St. Helens erupted. His last words were "Vancouver1, Vancouver 1. This is it!" A friend was watching Mount St. Helens erupt and survived. He was 150 miles from Mount St. Helens. He said it was so huge that it looked like Mt. Rainier.
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Photos credits: Ed Cooper
Photos credits: Gary Braasch
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