Thursday, December 1, 2016

Obsidian


The Many Shades of Obsidian
Obsidian is a naturally occurring, volcanic glass, the result of rapid cooling during it formation.
Bright & shiny when simply lying on the ground in it natural state, obsidian is hard to ignore. Anyone who spends time hunting for an Indian artifact is apt to come upon obsidian arrowheads.
With its lovely luster, reasonable hardness and abundance in the permanently chic color of black, obsidian is also a fine addition to the jewelry maker’s stone palette.
Not all obsidians are just some shade of black.A few are surprisingly patterned or colorful as well.Did you know that there’s a group of Italian islands that produce black obsidian flecked with white“blooms” that look like Oregon’s and Utah’s famous “flowering” or “snowflake”?Or that the “snowflakes” are a result of the obsidian’s gradual transformation into a crystalline rock?You might of know that but I bet your friends or customers won’t.

Alamasite also called peanut obsidian is sprinkled with 3-8mm diameter red “jaspery” little spheres set in a background of dark gray to black, somewhat perlitic.
Well known to gardeners as a soil conditioner and to builders as an insulator, perlite is gray obsidian characterized by concentric banding and innumerable concentric cracks. It is found locally in Alamos, Sonora Mexico.

Apache tears: One of the best known varieties of obsidian.Apache tears are small, residual nodules of transparent to translucent black obsidian weathered out of massive perlite.The most famous and popular locality is at Superior, Arizona.Apache tears can also be found in Rome, Oregon. In Rome Oregon you can see the tears pretty easily lying on top of the white perlite ground cover.

Double flow obsidian:So called by Oregon and California rockhounds because of the exceptionally
twisted and convoluted “flow lines” in the material. The earliest use of this term was found in early lapidary
business in Oregon around 1941. These slabs were offered in 2x3 inch pieces for about fifty cents each.

Fire obsidian:Fire obsidian shows vibrant interference colors on very thin, twisting bands, which may be the result of flow patterns before the material cooled.The best pieces are superb gemstones suitable for fine jewelry.
This type of obsidian presumably comes from the Glass Butte area in Oregon.We (certain club members) still have not been so lucky to find it.

Flame obsidian:Flame obsidian, like fire obsidian, has dramatic iridescent colors.This is a hard to find type obsidian, but some specimens have been found at Richardson’s Rock Ranch, formerly The Priday Ranch. I’ve been up to the ranch mines, but have not seen much obsidian.Has anyone else?

Mahogany obsidian:
An attractive reddish-brown variety. It apparently owes its attractive mahogany color to the oxidation of finely dispersed iron minerals, such as magnetite.This type is found at Glass Butt Oregon and Davis Creek California.
The club has been to both places and it is quite easy to find just lying on the ground.

Rainbow obsidian:Rainbow shows its spectral colors dramatically in the black obsidian.The colors apparently arise from interference effects stemming form the alignment of very tiny rods of the mineral hedenbergite. This type of obsidian is found at Glass Butt Oregon, but we (the club) like to go to the Davis Creek area in California for large specimens.

Snowflake obsidian:Also called flower or flowering obsidian, this high-contrast patterned material has been exploited as a gem since the mid 20th century.It is characterized by very small white spheres from a few millimeters or less to perhaps two centimeters across. The white snowflakes, often identified as cristobalite, a high-temp form of silica, are the results of the obsidian devitrifying or rearranging itself into a more orderly material than a glass: alkali feldspar is also an important component.

We all know there are lots of different names for obsidian.Not all are listed here but the ones that are listed are the most popular. Silver-lace or pink types of obsidian that we (the club) all know from the Glass Butt area, but there are still more. If you have a good spot that you have found gem worthy obsidian please let us all know.
(Lapidary Journal July 2010)

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