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Jewelry, Gems, & Minerals/Slag Glass or Natural?


I have a "rock" here that I was told was natural from the Oregon area. My research leads me to believe it might actually be slag glass. I'm still holding out hope that it is not man made though. I don't see any slag glass with the solid white "bubbles" for lack of a better word. So maybe it isn't slag glass? Would some kind of lava/obsidian look like this or is that wishful thinking? Thank you!

Hi Star,

There is indeed some green obsidian found in Oregon. However, the green Oregon obsidian is usually greenish grey and opaque, never really clear and transparent. Your sample is very clear and that is the trademark of slag glass. From the looks in your picture I would go with slag glass.
To be absolutely sure you could have some chemical tests done (XRF - X-Ray Fluorescence). I am afraid that this would only confirm your suspicion that this is slag glass.  

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Uwe Richard Kackstaetter, Ph.D. (Dr.K)


I can answer questions concerning minerals, mineralogy, gems, metals, and anything that has to do with geology. However, I am NOT a jeweler. Questions about values, settings, gem stone cuts and appraisals are best directed to other experts on this site. I can however aide in the identification of unknown mineral materials. As a public service and part as training for new geoscientists, our university department provides FREE mineral identification for individuals. Please contact me for details or go to for details..


I am a professor of applied geology and mineralogy with many hours of field experience. Furthermore, I enjoy recreational gold prospecting and mineral collecting. As a professor I am engaged in research concerning minerals and their occurrence.

Member of the GPAA (Gold Prospectors Association of America) as well as the Association of Environmental Geochemists. Member of the GSA (Geologic Society of America) Member of the AIPG (American Institute of Professional Geologists)

Here is a small sampling: Mineral-rock handbook: Rapid-easy mineral-rock determination : written for anyone interested in minerals and rocks - Proctor, Peterson, and Kackstaetter;Macmillan Pub. Co. (New York and Toronto and New York) Physical Geology Laboratory e-Manual [CD-ROM], Kackstaetter, Earth Science Education LLC Colorado Front Range Self-guided Geology Field Trips, Kackstaetter,

Ph.D. in Applied Geology and Mineralogy. I am actively teaching courses in mineralogy and a variety of field courses with mineral collecting opportunities. Background in precious metal exploration.

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