![]() Shackley at the University of California at Berkley and research done as part of the Preservation Fellowship Program at the private non-profit organization Archaeology Southwest has shown that the Mule Creek Obsidian Deposits were extensively mined and utilized by early cultures, and that the raw obsidian nodules and probably partially finished products (called blanks) were widely utilized and traded within in New Mexico and Southern Arizona. Because of its limited occurrence, good sources were highly sought after by prehistoric cultures, most likely fought over, and became the basis of early production centers, commerce, and trade routes.Īrchaeological research of the late pre-historic cultures of the American Southwest and Northern Mexico conducted by Dr. Obsidian has been a treasured natural resource of prehistoric and historic cultures worldwide since the beginning of the Stone Age because of its glassy composition and conchoidal fracture, allowing the rock to be easily worked into extremely sharp projectile points, cutting blades and other tools. Perlite layer within Mule Creek rhyolitic ash flow When found in place, the obsidian occurs as small nodules, generally two inches (5cm) or less in diameter, but occasionally up to twice that size, within outcrops of perlitic ash-flow deposits that absolute dating shows were ejected 17.7 million years ago. Within this vast area that includes portions of Grant and Catron Counties in New Mexico and Greenlee County in Arizona, are numerous, extensive obsidian-bearing volcanic rhyolitic ash flow deposits. The deposits are located about 20 miles northwest of the Casitas and occur within a greater than 100 square mile area that centers around the small community of Mule Creek, New Mexico, about five miles from the Arizona border. Steven Shackley, Department of Anthropology at the University of California at Berkley, regarding archaeological sources and use of obsidian in the American Southwest indicates that the Mule Creek Obsidian Deposits are probably the most extensive occurrence geographically of obsidian anywhere in the Southwest. If a rapidly cooled, rhyolitic magma contains 2% or more water to start with, then the resultant volcanic glass will solidify as perlite, not obsidian.īroken Marekanites displaying conchoidal fractureĮxtensive research by M. Not all perlite deposits form from hydration of obsidian, however. Thus, many volcanic deposits that originally formed as obsidian are now entirely converted to perlite. The reason for this is that over time, ever so slowly, obsidian absorbs water into its structure, and once that happens the obsidian converts to another natural glass or mineraloid called perlite. ![]() Obsidian is not stable at the earth’s surface and consequently is rarely found in rocks more than a few tens of millions of years old. ![]() Similar deposits of obsidian occur just south of the border in the Mexican States of Sonora and Chihuahua. In the United States, obsidian occurs in most western states and is abundant within western New Mexico and Arizona. Obsidian is found around the world wherever rhyolitic magma (containing 70% or more SiO 2 and less than 2% water) occur. Perlite showing bedding layers and swirling texture Sometimes it may contain inclusions of small, white crystals of the mineral cristobalite, a high-temperature form of SiO 2, or it may contain linear or swirling patterns of extremely small gas bubbles retained within the flowing magma or lava before it was rapidly cooled. Obsidian is easily identified by its glassy, conchoidal fracture and its brown or smoky-gray to black color. Typically, obsidian contains between 70 and 75% SiO 2, substantial amounts of magnesium oxide (MgO) and iron oxide (Fe 3O 4), plus numerous trace elements, such as rubidium (Rb), cesium (Cs), strontium (Sr), barium (Ba), lanthanum (La), cerium (Ce), yttrium (Y), titanium (Ti), zirconium (Zr), phosporous (P), tantalum (Ta) or niobium (Nb). Instead it is a naturally-occurring amorphous volcanic rhyolitic glass, formed when a magma or lava flow, highly rich in SiO 2 cools so rapidly that crystalline minerals do not have time to form. In geologic terms, obsidian is classified as an extrusive igneous rock or sometimes a mineraloid, but never as a mineral because it does not have a crystalline structure. Typical shapes of Mule Creek Marekanites size range averages 1 to 5 cm, although some may go as large as 10 cm.Īmong the wide range of volcanic rocks and minerals that can be found near Casitas de Gila Guesthouses, one of the most interesting is obsidian.
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