LOOKALIKE CHECK
A glassy black rock is not an identification
Short answer: A black, shiny specimen may be natural volcanic glass, industrial slag, or another material. A photo can record texture, bubbles, edges, and discovery setting, but it cannot prove obsidian or a meteorite.
Begin with a category, not a verdict
“Glassy black” describes an appearance. It is a useful first observation, but it is not a rock name. The safest first note is to separate what you can see from what you think it may be: black, reflective, no visible crystals in this view, with or without rounded holes, and found in a particular setting.
Do not let a photo match turn that note into a certificate. Light, polish, wetness, and a weathered rind can all change how dark or glassy a surface looks in a picture.
Why obsidian and slag can look alike
Obsidian is natural volcanic glass. USGS describes it as glassy material formed when lava cools so quickly that crystals do not have time to grow. Existing edges may show a curved, shell-like break, but a photograph still cannot establish its origin.
Slag is a human-made by-product of metal processing. The National Park Service notes that cooled smelter slag can resemble obsidian. A shiny black, glass-like appearance therefore does not distinguish a natural specimen from industrial material by itself.
Record these visible clues without damaging the specimen
- Surface: Is it uniformly glassy, dull in places, coated, or weathered?
- Texture: Are there visible crystals, small rounded holes, layered material, or a smooth glassy mass?
- Edges: Examine an edge that already exists. Describe it as curved, irregular, jagged, or flat rather than making a new break.
- Setting: Was it found near volcanic terrain, a stream, landscaping aggregate, a railroad bed, an old industrial site, or unknown fill?
- Scale: Photograph the whole specimen and one close view with a scale nearby but not covering the surface.
Rounded holes are worth recording, not diagnosing. USGS notes that vesicles are common in some volcanic rocks and can also occur in metallic slag; they are not evidence that a specimen is a meteorite.
Do not use a photo to certify a meteorite
A meteorite claim needs in-person examination. USGS advises that a suspected meteorite cannot be confirmed from a photograph alone. If that possibility matters, keep the specimen and its location notes intact, avoid destructive tests, and ask a museum, geological survey, or qualified meteorite specialist how to submit it for review.
The useful photo result may simply be glassy black material; origin undetermined from the image. That is an honest starting point for a later comparison.
Use the tool as an observation prompt
Try the rock identification tool for a tentative visual description, then compare the result with the evidence checklist in our guide to checking an AI rock identification. If you know where the specimen came from, preserve that context with a short location note; it may help a person assess the specimen later, but it does not prove the name.
Sources for this guide
This guide supports careful observation. It does not identify a meteorite, establish provenance, or replace an in-person examination.