Obsidian
SpiritRock Shop
Polishers Laps Saws

Obsidian is a rock which is a type of naturally occurring glass, produced by volcanoes (igneous origin) when a
felsic lava cools rapidly and freezes without sufficient time for crystal growth. It is commonly found within the
margins of felsic lava flows, where cooling is more rapid. Because of the lack of crystal structure, obsidian blade
edges can reach almost molecular thinness, leading to its ancient use as arrowheads and its modern use as
surgical scalpel blades.
While a rock like basalt is dark because of ferromagnesian enrichment, obsidian consists mainly of silicon dioxide,
usually 70% or more. Obsidian is mineral-like, but not a true mineral because it is not crystalline. Its composition is
very similar to that of granite and rhyolite. It is sometimes classified as a
Mineraloid because obsidian is
metastable at the earth's surface (over time the glass becomes fine-grained mineral crystals). The breakdown of
obsidian is accelerated by the presence of water. Tektites were once thought by many to be obsidian produced by
lunar volcanic eruptions, though few scientists now agree with this theory.

While pure obsidian is always dark in appearance, the color varies depending on the presence of impurities. Iron
and magnesium typically give the obsidian a dark green to brown to black color. In some stones, the inclusion of
small, white, radially clustered crystals of
Cristobalite in the black glass develop a blotchy or snowflake pattern
producing what is known as


Snowflake Obsidian




It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten
rock was flowing before being cooled.

These bubbles can produce interesting effects
such as a golden or silver sheen, known as
Sheen Obsidian





or a multi-color rainbow sheen known as

Rainbow Obsidian





Another type of Obsidian called
Tri Flow Obsidian
has a mix of red/brown, black and clear swirls
or layers in it making it popular for knapping.



Another popular type has relatively equal swirls of red,
brown or golden coloring mixed with a black.
This is referred to as                   
Mahogany Obsidian
as the swirls much resemble a woodgrain pattern.


Obsidian is relatively soft with a typical hardness rating of 5 to 5.5.  Obsidian, unlike crystals, has no regular
structure and therefore fractures in smooth conchoidal (curved) shapes. The intersections of these fractures can
form edges sharper than the finest steel blades. For this reason, obsidian was used by many native cultures to
make arrowheads and blades.
The Nevada, Utah and California area, referred to as the Great Basin, is an ideal location to find Obsidian. There
are a myriad of colors, patterns and mixes of Obsidians, making them a very desirable collector item.
Click on any photo to see a larger version
Official PayPal Seal
Item # 28OBS01130650
Mahogany Obsidian Rough
$16.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 1 lb 13oz or 1.8 lbs (830g)
and measures 6.8 x 2.9 x 2.7"  
(17.2 x 7.3 x 7cm)
Notice
These specimens are relatively inexpensive to purchase but expensive to ship due to the weight. We ship US Post Office Priority Mail,
Generally Flat rate boxes. We charge exact shipping cost + insurance cost + $3.00 for packing materials. Please consider buying
multiple pieces as shipping is the same for 2 to 6 lbs and again from 6lbs to 10lbs. If multiple pieces fit in a flat rate box and you paid
more shipping than is required we will refund excess shipping charges paid. Orders over 10 lbs may ship UPS Ground
This Mahogany Obsidian listed Below from Glass Butte, Oregon tends to have a mix of
layered clear possibly making it a combination of Mahogany & Tri-Flow  
Item # 29OBS01136170
Mahogany Obsidian Rough
$19.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 2 lb 6oz or 2.38 lbs (1080g)
and measures 6.4 x 3.9 x 3.1"  
(16.4 x 9.9 x 7.9cm)
Item # 30OBS01131510
Mahogany Obsidian Rough
$5.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 0 lb 8oz or 0.5 lbs (228g)
and measures 2.7 x 2.2 x 1.5"
(7 x 5.7 x 3.8cm)
Item # 31OBS01137720
Mahogany Obsidian Rough
$8.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 14.7oz or 0.92 lbs (418g)
and measures 2.9 x 2.7 x 2.4"
(7.6 x 6.9 x 6.1cm)
Item # 32OBS01132320
Mahogany Obsidian Rough
$7.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 12.3oz or 0.77 lbs (348g)
and measures 3.7 x 2.3 x 2.3"
(9.4 x 6 x 6cm)
Item # 33OBS01133310
Mahogany Obsidian Rough
$5.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 7oz or 0.44 lbs (198g) and
measures 3.1 x 2.1 x 1.4"
(8 x 5.5 x 3.6cm)
Item # 34OBS01131030
Mahogany Obsidian Rough
$10.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 16oz or 1 lbs (460g) and
measures 3.8 x 3.5 x 1.6"
(9.7 x 9.1 x 4.1cm)
Item # 35OBS01134630
Mahogany Obsidian Rough
$11.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 1 lb 3oz or 1.21 lbs (550g)
and measures 4.6 x 2.8 x 2.1"
(11.6 x 7.1 x 5.5cm)
Item # 36OBS01134420
Mahogany Obsidian Rough
$8.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 13oz or .81 lbs (370g) and
measures 3.5 x 2.7 x 2.5"
(9.1 x 6.8 x 6.5cm)
Item # 37OBS01137420
Mahogany Obsidian Rough
$8.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 13oz or .82 lbs (372g) and
measures 4.2 x 3 x 1.5"
(10.7 x 7.7 x 4cm)
Item # 38OBS01131810
Mahogany Obsidian Rough
$6.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 9.4oz or .59 lbs (268g) and
measures 2.6 x 2.1 x 2.1"
(6.8 x 5.5 x 5.5cm)
Item # 39OBS01138020
Mahogany Obsidian Rough
$7.00
Mahogany Obsidian from Glass
Butte in the high desert area of
Central Oregon
(photographed wet to show color)
weighs 11oz or .69 lbs (314g) and
measures 3.9 x 2.2 x 1.6"
(10 x 5.7 x 4.1cm)