01
Texture and grain size
Look for glassy, fine-grained, coarse-grained, crystalline, fragmental, or clastic texture and whether grains are visible, rounded, interlocking, sorted, or cemented.
Practical guide
What rock is this?
Several clear photos can help you form a possible rock, mineral, crystal, gem, or fossil match by comparing visible texture, grain size, structure, and context. A photo cannot confirm chemical composition, treatment, origin, authenticity, safety, or value, so use the result as a hypothesis to test.
Start a photo identification
iPhone · Up to four photos and optional find context
What to look for
Read the specimen as a group of clues
Color is memorable but often variable. A stronger candidate explains the specimen’s texture, grains or crystals, structure, and geologic setting together.
02
Visible minerals and luster
Record distinct crystals, color zones, metallic or nonmetallic luster, transparency, streak already visible on the specimen, and whether color changes across fresh and weathered surfaces.
03
Structure and form
Compare layering, banding, foliation, vesicles, fossils, crystal faces, cleavage-like planes, fracture, inclusions, and the overall shape without breaking the specimen.
04
Geologic context
Note a broad locality, outcrop or loose find, surrounding rock, landscape, and any reliable map unit. Do not remove material where collecting is prohibited or expose a sensitive site.
Step by step
How to identify a rock from photos
- 01
Photograph several useful views
Use bright indirect light, a plain background, and a neutral scale reference. Include the whole specimen, a fresh-looking surface if one already exists, close-ups of grains or crystals, and up to four angles without filters or digital zoom.
- 02
Describe only what you can observe
Record texture, approximate grain size, layering, vesicles, luster, visible crystals, fossils, fracture, weathering, and where it was found. Color alone is rarely enough, and a photo cannot measure hardness, streak, density, magnetism, or chemistry.
- 03
Test the candidate against alternatives
Ask whether the proposed match explains every visible clue and the geologic context. Compare likely alternatives, distinguish a rock from a mineral or manufactured material, and use authoritative maps and collection references.
- 04
Avoid destructive home tests
Do not cut, grind, drill, polish, burn, taste, or use chemicals on an unknown specimen just to validate an app result. Dust-producing work on rock can create respirable crystalline silica and requires appropriate professional controls.
- 05
Escalate consequential questions
Use a qualified geologist, mineralogist, gemologist, museum specialist, or laboratory when the answer affects authenticity, treatment, origin, meteorite status, hazardous material, sale, insurance, or value.
Inside the app
Collect evidence before you collect certainty.
These are actual Rock Identifier screens. The app organizes a possible match, physical and geological context, follow-up questions, and illustrative estimates; it does not authenticate a specimen, measure its properties, certify safety, or provide a professional appraisal.
Try the app
Turn a specimen photo into a testable shortlist
Rock Identifier accepts up to four selected photos and optional find context, then suggests a possible specimen, organizes reference details and follow-up questions, and saves results in a private collection. Keep expert examination and laboratory testing separate when the answer matters.
Primary references
Compare appearance with geology—and know what a photo cannot test.
These references support the classification, mapping, collection, and silica-dust boundaries in this guide. They do not endorse Rock Identifier; U.S. maps do not cover every country.
- National Park Service — How Rocks Are ClassifiedAn official overview of igneous, sedimentary, and metamorphic rocks, their formation, texture, grain size, and classification.
- USGS — Cooperative National Geologic MapA map-based way to compare U.S. locality and geologic-unit context and find more detailed state and national geological references.
- Smithsonian National Museum of Natural History — Mineral Sciences CollectionsCollection context for rocks, ores, minerals, gems, and meteorites and the scientific evidence used to study them.
- CDC/NIOSH — Silica and Worker HealthOfficial guidance on respirable crystalline silica exposure from dust-generating work such as cutting, grinding, drilling, and polishing stone.
- USGS — The Properties of MineralsA classic USGS reference describing observable and measured properties such as color, streak, hardness, cleavage, crystal form, and specific gravity.
Direct answers
Rock and mineral identification questions
How can I identify a rock from a picture?
Use several clear photos and compare texture, grain size, visible minerals, luster, layering, vesicles, fossils, fracture, weathering, and geologic context. Treat the suggested name as a candidate and compare it with authoritative maps, collection records, and plausible alternatives.
Which photos are best for rock identification?
Include the whole specimen, multiple angles, a neutral scale reference, and close-ups of grains, crystals, layers, fossils, vesicles, fracture, and any naturally exposed fresh-looking surface. Use bright indirect light and avoid filters, heavy shadows, digital zoom, and an artificial wet shine.
Can a photo identify an exact rock or mineral?
Not reliably in every case. Photos do not measure hardness, streak, density, magnetism, optical properties, or chemistry, and many specimens share a similar appearance. Direct examination or laboratory analysis may be needed.
Can Rock Identifier confirm a gemstone or meteorite?
No. A photo cannot confirm gemstone authenticity, treatment, origin, professional grade, or meteorite status. Use an independent gemologist, geologist, meteorite specialist, or qualified laboratory for confirmation.
Can the app tell me exactly how much a specimen is worth?
No. Any range is an illustrative estimate, not an appraisal or guaranteed sale price. Identity, authenticity, treatment, size, weight, quality, condition, provenance, laboratory reports, venue, fees, and current demand can all change value.
Is it safe to cut, grind, or polish an unknown rock?
Do not start dust-producing or destructive work based on an app result. Cutting, grinding, drilling, and polishing rock can create respirable crystalline silica, and an unknown specimen may present other hazards. Use appropriate professional identification, controls, and local guidance.