![]() ![]() In some stones, the inclusion of small, white, radially clustered crystals of cristobalite in the black glass produce a blotchy or snowflake pattern ( snowflake obsidian). Iron and magnesium typically give the obsidian a dark green to brown to black color. Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis. Obsidian has a low water content when fresh, typically less than 1% water by weight, but becomes progressively hydrated when exposed to groundwater, forming perlite. This breakdown of obsidian is accelerated by the presence of water. Because obsidian is metastable at the earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. Crystalline rocks with obsidian's composition include granite and rhyolite. Obsidian consists mainly of SiO 2 ( silicon dioxide), usually 70% or more. Though obsidian is dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. It is sometimes classified as a mineraloid. Hailing this remarkable achievement, the researchers say the old axe makers “creatively solved through convergent thinking technological problems such as effectively detaching and shaping large flakes of the unusually brittle and cutting volcanic glass.Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline in addition, its composition is too complex to comprise a single mineral. According to the authors, the adaptation of existing flint knapping techniques to create more challenging obsidian tools can be seen as an example of “convergent thinking”, which is associated with creative problem-solving. ![]() The emergence of such abilities marks a surprisingly massive cognitive leap for such an ancient group of humans. And yet, when describing tools from over a million years ago, the study authors say that “the standardized obsidian handaxes provide ample evidence of the repetitive use of fully mastered skills.” Techniques for shaping obsidian are believed to have first emerged during the Upper Paleolithic, and even modern knappers wear protective gloves to avoid shredding their hands when working with the razor-sharp material. “Accordingly, manufacturers had to accurately evaluate the strength of the blow to avoid producing flakes of little use, or just to avoid smashing the core,” explain the researchers. “We show through statistical analysis that this was a focused activity, that very standardized handaxes were produced and that this was a stone-tool workshop,” they write.ĭescribing the axes, the researchers repeatedly marvel that “the morphological standardization is remarkable,” and while they don’t know which species of human crafted the tools, they say that whoever created them diligently applied “secondary retouches” and was highly “focused on the final regularization of the artifacts.”Īchieving such homogeneity would have required highly sharpened skills and a fair amount of dexterity, as obsidian is a fragile rock that must be knapped with considerably more finesse than flint or basalt. However, during the course of their excavations, the team came across an ancient layer of sediment containing a cache of 578 stone tools, all but three of which were sculpted from obsidian. “Generally speaking, obsidian is extensively used only from the Middle Stone Age onwards,” write the study authors. Located predominantly in France and the UK, the most notable Stone Age axe workshops were all associated with the creation of flint blades. “ sites described as ‘knapping workshops’ are only recorded in the second half of the Middle Pleistocene and only in Europe so far,” write the researchers. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |