Obsidian Tumbling Secrets

Obisidian is a very common extrusive igneous rock. It is composed of the smae minerals as granite, but cooled so rapidly that different minerals don't have time to crystialize.

It is natural black glass that often has visible inclusions of water, feldspar crystals or iron. Water inside microscopic air bubbles can act as a prisms to light and cause a rainbow effect inside the obsidian.

Feldspar can crystalize within the obisidian as white "snowflakes," hence the name snowflake obsidian.

Iron can oxidize in bands caused by the flow of obsidian while it is still liquid, causing brown swirl patterns to form. This is known as mahogany obsidian.

Obsidian is the same hardness as man-made glass, and cannot be tumbled with other stones.

"Apache Tears" are small blebs of obsidian that formed within a glassy rhyolite. They are semi transparent and have a long legend that goes with them.

To tumble any type of obsidian in a rock tumbler, follow these simple procedures:

1. Complete steps 1 and 2 as you would any agate (with obsidian as the only stone in your tumbler). You might find that cutting down the length you run them from 7 to 5 days is good enough.

2. When you load step 3, replace 1/2 the water with corn syrup. This will thicken the solution, which makes the process slow down. This step will also keep the obsidian from chipping and scratching itself. If this trick doesn't solve all of your chipping problems, add plastic pellets and more corn syrup. Let your rock tumbler run for 7 days in this stage.

3. For the final polish use TIN OXIDE ONLY. Cerium may work OK, but not as good as tin oxide. Aluminum and titanium don't work at all on obsidian. Once again replace at least half the water with corn syrup. Do use fresh plastic pellets. Don't try washing and re-using the pellets from the previous step.

Here is the final trick: Let your rock tumbler run for up to 3 weeks in the final polish stage. Check you rocks once a week to make sure they are progressing.

I have used this process in 3 to 40 lb tumblers with great success.

If you have questions, just e-mail or call. rockshop@rocks4u.com 801-355-7952

Good luck--Rick