The image above shows a dark green stone with a shiny, glass-like surface. The text describes a parent who received it from their son over twenty-five years ago and wants to know what it could be. This is a common question, and there are several possibilities. The most likely candidates are obsidian, a volcanic glass, or slag glass, a man-made byproduct.
How to Tell Obsidian from Slag Glass
The key to identifying your stone is to look at its physical properties and where it came from.
Obsidian, or volcanic glass, is a natural material. It forms when lava cools very quickly. It is very hard and has a smooth, glassy texture. It often appears black, but it can also be dark green or brown. When it breaks, it creates sharp, curved edges known as conchoidal fractures.
Slag glass is a man-made byproduct. It is created during industrial processes, such as smelting. It can look very similar to obsidian, but it often contains bubbles or impurities. It is also typically found near industrial sites or old factories.
What to Look For
There are a few simple tests you can do to help identify your stone.
First, check the hardness. Obsidian is quite hard. If you can scratch it with a piece of quartz, it is likely not obsidian.
Second, check the transparency. Hold the stone up to a light. Obsidian is usually opaque or slightly transparent. Slag glass may have a more uniform transparency or contain visible bubbles.
Third, consider the location. Where was it found? If it was found in an area with volcanic history, obsidian is a strong possibility. If it was found near a factory or industrial area, slag glass is more likely.
The Value of Your Stone
While obsidian is not a precious gemstone, it is a beautiful and interesting mineral. It has been used for tools, jewelry, and decorative objects for thousands of years. Even if it is slag glass, it can still be a lovely keepsake, especially since it was a gift from your son.
Final Thoughts
The stone in the image is most likely a piece of dark green obsidian or slag glass. To be certain, you could take it to a local rock shop or a geological society. They can examine it in person and give you a definitive answer. Regardless of its origin, it is a unique and interesting piece.
Have you ever found a stone you could not identify? Share your story in the comments below.
