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Roger Weller, geology instructor

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Obsidian
Stormy Wall
Physical Geology
Spring 2005
 

Obsidian Obsession
 

Obsidian was once thought to be a stone that could banish demons.  In Hawaii it is thought to be the blood of the ‘Mother’ as she gives birth through her volcanic activity (Armitage). Obsidian may not drive out demons but it seems to have certain powers.  The power to dazzle being just one.  It is an igneous rock, a rock produced under conditions of intense heat.  Igneous rocks are formed from a molten mixture of minerals, usually rich in gases, called magma.  However, because obsidian is not made up of mineral crystals it is not considered a true rock.  It is actually a congealed liquid with minor amounts of microscopic mineral crystals and rock impurities (Miller). Obsidian was named for the Roman Obsius who is said to have first discovered obsidian in Ethiopia.










 

 


Copyright 2005 by Andrew Alden, geology.about.com, reproduced under educational fair use

 

Igneous rocks usually contain iron and magnesium minerals in addition to feldspar or feldspar-like minerals and many igneous rocks contain quartz. Igneous rocks rich in light minerals such as quartz and feldspar, are called acidic.  They are light in not only color but in weight, with an average specific gravity or density of 2.6 to 2.7.  Igneous rocks richer in iron and magnesium minerals are called basic.  They are darker and heavier with a specific gravity of 3.0 or more. Obsidian’s specific gravity ranges from 2.3 - 3.0.  Igneous rocks encompass those with large crystals to glassy rocks such as obsidian with little or no crystals. 

If magma cools beneath the surface of the earth, intrusive rocks are formed. Obsidian is an extrusive rock rather than intrusive.  Extrusive rocks are formed by magma that rises to the surface of the earth.  There are many extrusive rocks with the most common being lava.  These rocks range from light (acidic) to dark (basic).  As with all igneous rocks, intrusive or extrusive, extrusive rocks range from those rich in quartz to those with no quartz at all.  Most extrusive rocks such as obsidian are fine-grained due to rapid cooling. 

Obsidian is chemically the same as rhyolite a very fine textured acidic rock. However obsidian is formed when rhyolite lava enters the water and is quickly cooled.  The result is a glassy textured rock, obsidian, also known as natural glass or volcanic glass.  Obsidian is rich in silica and low in water.  Its hardness is 5 - 5.5, softer that quartz but about the same hardness as window glass. 

There are many varieties of obsidian and it can be found in a wide range of colors from dark browns and blacks to greens depending upon the amount of iron and magnesium it contains. In addition, obsidian can be found containing bubbles that cause interesting effects.  These effects, known as sheens, can range from yellows, golds, blues, purples, and even rainbow. Sheen Obsidian has a golden sheen and Rainbow Obsidian has a rainbow sheen. Obsidian can also be found containing white crystal cluster inclusions. This obsidian is known as Snowflake Obsidian.  Because of its attractiveness, obsidian is often used as a semiprecious stone.  It is fragile however, and care must be taken to avoid striking it as it might crack.

Obsidian can be found in many areas around the world from Obsidian Cliff in Yellowstone National Park in Wyoming, USA to Scotland, Italy, Iceland and Hawaii.  In the United States, dark pieces of obsidian can be found in Arizona and New Mexico and are called Apache Tears.  In Iceland it is called Iceland Agate.

While some minerals have cleavage, or will split along a plane related to their structure, obsidian has no cleavage plane and breaks irregularly with what is called a conchoidal or ‘shell form’ fracture.  The fractured surfaces of obsidian can be razor sharp.  It is believed that in North America, the Native Americans utilized most of the obsidian sites and probably quickly discovered the versatility and value of Obsidian. Obsidian became a valuable trading commodity and was conveyed over great distances.  It is interesting to note that obsidian sites have their own unique properties and by using trace element analysis, it has been possible to pinpoint the original location of many artifacts made from obsidian.  

Mankind, as far back as prehistoric times, has used obsidian in a variety of ways.  It was vital in the making of knives, arrowheads and spearheads, fishhooks, jewelry, masks, and even mirrors.  In addition, obsidian has been and continues to be used for medicinal purposes.  It is possible to purchase Obsidian Gem Elixir as a homeopathic medicine.  Obsidian used for medicinal purposes is said to improve the focus of the mind, help to overcome obsession, and align your energy bodies.  Obsidian is also used to promote digestive health and reduce pain and inflammation.

During spring break of 2005, I had the opportunity to visit Sunset Crater Volcano National Monument in Flagstaff, Arizona, USA. Sunset crater is in the eastern part of the San Francisco volcanic field and the obsidian sources found in this field are considered by some as the best studied in the Southwest (Shackley). The visitor center had a nice display featuring volcanic activity, all computer generated, as well as various pieces of obsidian and other volcanic rocks. I found it remarkable that something as beautiful as obsidian could result from the destructive power of a volcano.

In conclusion, obsidian is an igneous extrusive natural glass of volcanic origin formed by the rapid cooling of lava. With its wide range of colors and varieties it is not only an attractive stone it is also a stone with a vast and varied history.  It is found throughout the world and one particularly good site where an individual can still find fist-sized or bigger pieces of obsidian is Glass Buttes in central Oregon, USA (Miller). I find obsidian to be mystical and alluring.  It imparts an illusion of being a solid color when in actuality it is translucent. Obsidian may indeed hold magical powers.  If so, I believe the power may be in its beauty.  I was drawn to it and was not able to leave Sunset Crater without buying a small polished piece.

 

 

Works Cited

 

 

            Alden, Andrew. Geology Obsidian. About .com. 23 April 2005

           
http://geology.about.com/library/bl/images/blobsidian.htm

 

            Armitage, John. Crystals and Their Properties. Mahatma Shamballa

 

Multidimensional Healing Network Site. 23 April 2005

 

http://www.mahatma.co.uk/crystal_manual/crystals/obsidian.htm

            Miller, Jim. Obsidian Is Hot Stuff.  23 April 2005

 

 http://volcano.und.edu/vwdocs/vw_hyperexchange/obsidian.html

             Shackley, M. Steven. Petrology of Silicic Glasses in the Southwest. University of

 

California at Berkeley. 23 April 2005

            http://www.swxrflab.net/obspertrl.htm