You pick up a heavy grey stone on a beach, or a glittering piece of something in a quarry, and you want to know what it is. A photo is the obvious first step. It gets you part of the way, and it helps to know which part. If you want a suggestion straight from a photo, LithoCanvas is an Android app by Senorit that gives one.
Five checks before you open any app
- Colour and pattern. Note the colour inside as well as outside if the stone is broken. Colour alone is a weak guide, because one mineral can show several colours and different minerals can look alike.
- Grain. Can you see separate crystals, rounded sand grains or nothing at all?
- Weight. Compare it with another stone of the same size.
- Hardness. Try to scratch it, and try to scratch it with something. Geologists rate hardness by finding the hardest material a sample can scratch or the softest material that scratches it, and only a permanent scratch visible to the naked eye counts. Glass is about 5.5 on the Mohs scale and ordinary steel about 4 to 4.5.
- Streak. Drag the stone firmly across unglazed porcelain, for example the unglazed bottom of a bowl, and look at the colour of the powder. The streak is often more consistent than the surface colour. It only works for minerals softer than the plate, and hard minerals mostly leave a white streak.
Igneous, sedimentary or metamorphic
Crystals that grew as a melt cooled suggest an igneous rock such as granite or basalt. Flat layers, visible sand grains or fossils suggest a sedimentary rock such as sandstone or limestone. Bands or a sheet-like grain from heat and pressure suggest a metamorphic rock such as gneiss or marble. The boundaries are not sharp, so treat this as a first guess.
Three photos to take
- A sharp, dry photo in daylight.
- A close-up of the surface or of a fresh break, if you can look at one safely.
- One with a coin next to the stone for scale.
What a photo cannot tell you
A photo cannot show hardness, and it says nothing about where the stone came from. Write down the find spot. For beach finds there is a guide to flint and common beach stones, and for a stone with a natural hole see hag stones. If you think a round rock might be hollow, read how to tell if a rock is a geode.
What type of crystal or gem is this?
The same limits apply. A glassy shine with visible crystal faces is a clue. Check hardness and streak, and test any name you get from an app or a forum.
How LithoCanvas fits in
LithoCanvas is an Android app by Senorit for this kind of sorting. You photograph a rock, crystal, gemstone or painting and it suggests what it is, with a confidence shown as a percentage and a high, medium or low band. For each mineral it shows hardness, crystal system, colour and lustre, and a glossary explains the terms.
The suggestion comes from a statistical model. It is an estimate, and confidence values are not guarantees. The app does not judge authenticity and gives no price. If a find matters to you, ask a mineralogist or a geologist. The app's own page on the topic is lithocanvas.de, and its Mohs hardness page explains the scale.
Your photo goes to an outside service
When you identify an object, LithoCanvas sends the photo to Google Gemini, run by Google LLC in the USA, and only after you agree. Without that consent identification is not available. The AI notice and the privacy policy describe it in full.
Questions and answers
Is a rock identifier app accurate?
Results are suggestions from a statistical model, and a confidence value is not a guarantee. Use them as a starting point and check hardness and streak yourself.
How do you identify a rock by picture?
Take a sharp photo with a coin for scale, note colour and grain, and compare the result with simple tests. A picture alone cannot show hardness.
What is the difference between a rock and a mineral?
A mineral is a naturally formed crystalline substance. A rock is usually made of one or more minerals. Volcanic glass is a rock without crystals.
What you need
LithoCanvas needs Android 11 or newer and is aimed at people aged 18 and over. The download is free, and every account gets 5 free identifications once. Plans and prices are on the LithoCanvas page. Help is on the help page.