Snowflake Obsidian - Rock Tumbler Rough
This image shows a 3-pound bag of snowflake obsidian tumbling rough, dumped into a colander and sprayed with water to reveal its full color. Click on the image for a larger view.
Snowflake Obsidian Tumbling Rough
Size: mostly 1 to 2 inch pieces
What Is Snowflake Obsidian?
Snowflake obsidian is a product of a volcanic eruption. It formed when molten rock cooled so quickly that the atoms in the melt did not have enough time to arrange themselves into mineral crystals. Instead, the molten material immedately solidified into an amorphous solid called a "glass". So, snowflake obsidian can be called an "igneous rock" and a "volcanic glass".
What causes the snowflakes? Immediately after the rock formed it was completely black. Over time some of the glass started to alter into crystals of cristobalite, a white to gray mineral. So the white "snowflakes" are patches of cristobalite crystals within the volcanic glass.
Here are a few pieces of snowflake obsidian that we tumbled. It shapes quickly in a tumbler and produces bright black tumbled stones with gray to white snowflakes.
Does It Tumble Well?
Snowflake obsidian has a Mohs hardness of about 5 1/2 to 6. It is quite a bit softer than agate and jasper. That enables it to shape quickly in a rock tumbler. One week in a rotary tumbler in medium grit is enough time to round off all of the sharp edges and produce nicely-rounded stones. Then about four or five days in fine grit will have it ready to polish.
We always use TXP aluminum oxide polish when tumbling snowflake obsidian. It produces an excellent polish in six to seven days in rotary.
ADVANCED Rock Tumbling Recipe:
Snowflake Obsidian (1 to 2 inches)
These pieces of snowflake obsidian are about 1 to 2 inches in size and have a Mohs hardness of about 5 1/2. That is softer than most types of rocks that are processed in a rock tumbler. Obsidian also bruises easily if it is not cushioned. To accommodate these properties we do three things: 1) skip the coarse grit step; 2) tumble for a shorter amount of time in add plenty of media for cushioning.
1) Skip Coarse Grit: Coarse grit will quickly reduce the size of snowflake obsidian. So we skip the coarse grit step and begin our tumbling with medium grit (150/220 mesh).
2) Less Time: We also shorten the tumbling time in the first step. Instead of two weeks in 150/220 grit, we reduce that to 10 to 12 days. We also reduce the time in fine grit (500 mesh) to 5 days. Polishing time is not changed.
3) Media Needed: Snowflake obsidian bruises easily. To prevent bruising it should be swimming in a sea of small ceramic cylinder media We use about 50% ceramic cylinder media and 50% obsidian. The cylindrical shape of the ceramic media will enable them to act like roller bearings and provide a smooth tumbling action in the barrel. The many small pieces of media will also reduce the impact forces that occur in the barrel and deliver grit to all surfaces of the rough.
Recipe for Rotary Tumbling
Coarse Grit Step:
Snowflake obsidian is extremely "soft" so you do NOT need to use coarse grit.
Medium Grit Step:
Two tablespoons medium grit (150/220) per pound of rock and ceramic media. Add enough water to barely cover the rocks. You want 40% media and 60% obsidian. Let this tumble for 10-12 days. Rinse, clean and inspect the material. Tumble longer if more smoothing and shaping is desired.
Fine Grit Step:
If more media is needed to maintain barrel capacity, that media should be broken in and not new media with rough edges. Again, two tablespoons of fine grit (500F) per pound of rock and ceramic media. Add water to below the top of the rocks. Tumble for five days.
Barrel slurry dumped down the drain will harden like concrete.
IMPORTANT: Make sure that your barrel and rough have been cleaned thoroughly. Any grit carried over from a previous step will likely ruin your polish. Do not add more media at this point.
Measure two tablespoons of TXP Polish per pound of rock and ceramic media. Fill with water to just below the top of the rocks. Tumble for seven days.
Burnish If Needed:
Jasper, agate and petrified wood usually take a great polish. However, burnishing this material after the polish step can often improve the shininess of the finished stones. If you would like to try burnishing to see if it improves the look of your polished stones full burnishing instructions can be found here.
Finished Snowflake Obsidian Tumbled Stones:
If you don't want to tumble this snowflake obsidian yourself, we usually have medium size (5/8" to 1") tumbled stones of this material for sale by the pound. You can find them here.
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