Roger Weller, geology instructor
Obsidian was once thought to be a stone that could banish demons. In
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
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
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
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
Alden, Andrew. Geology Obsidian.
About .com. 23 April 2005
Multidimensional Healing Network Site. 23 April 2005
Miller, Jim. Obsidian Is Hot Stuff. 23 April 2005