Free tool
Rock identifier
Answer any of six quick questions and watch the likely candidates line up, each with the reasons it fits, what does not fit, and the one test that would settle it. No photo upload, no account.
Data last reviewed by Viral Tandel. Sources are listed with every entry.
How to use the rock identifier
- Clean a small spot. Scrub off dirt and look at a fresh, broken face if you can. Weathered skins change color and luster.
- Start with the reliable tests. Hardness and streak count the most in the scoring, color the least. You can answer the questions in any order and skip any of them.
- Do the scratch test. Press a fingernail, then a copper coin, then a steel knife into a smooth spot, and finally try to scratch a piece of glass with the rock. Rub each mark: a real scratch stays, a smear of metal wipes off.
- Do the streak test. Rub the rock hard across the unglazed back of a white bathroom tile and note the color of the powder.
- Try the two household tricks. Hold a cheap fridge magnet to it, and put one drop of white vinegar on a clean spot and watch for bubbles.
- Read the candidates. Each one shows why it fits, what does not fit, its tell-tale clue and what to test next. The panel at the top suggests the single test that best separates your top matches.
Tip
Wet the rock before you judge its color. Water shows the true color and pattern the way a polish would, then dries off without a trace.
What each question tells you
| Clue | How to test it | Why it matters |
|---|---|---|
| Hardness | Fingernail (about 2.5), copper coin (about 3), steel knife (about 5 to 5.5), glass (about 5.5) | The most reliable property you can test at home |
| Streak | Rub on an unglazed white tile | Hematite, magnetite and pyrite all look dark but streak differently |
| Luster | Tilt it under a lamp | Separates metallic ores from glassy and earthy minerals |
| Texture | Look with a 10x hand lens | Tells glass from fine-grained and coarse-grained rocks |
| Magnet, vinegar, weight | Fridge magnet, a drop of vinegar, heft it | Quick yes or no clues for magnetite, calcite, barite and pumice |
| Color | Wet the rock and look | Least reliable: quartz comes in almost every color |
Where the data comes from
The key covers common rocks, minerals and the usual look-alikes (slag, magnetite and iron meteorites among them). Every entry lists its sources, which you can open under each result: the Handbook of Mineralogy published by the Mineralogical Society of America, the University of Auckland rocks and minerals pages, the USGS Gemstones publication and Volcano Hazards glossary, the Washington University in St. Louis meteorite pages, and state geological survey pages. Hardness ranges for rocks, which are mixtures, are estimated from their main minerals and marked that way.
Heads up
The results are likely candidates, not a certain identification. Two rocks can pass every home test and still be different things. For anything that might be valuable, rare or a meteorite, get a second opinion from a rock club, a museum or your state geological survey.
Safety and the rules
Wear safety glasses when you break or scratch rocks, and never taste or lick an unknown mineral. Some minerals in the key, such as galena, contain lead, so wash your hands after handling them. Before you take a rock home, check who manages the land: collecting is not allowed in national parks, and other public lands have limits.
The data behind the identifier
All 66 rocks, minerals and look-alikes the identifier can suggest, with the hardness, streak and the one test that separates each from its look-alikes. Every entry in the tool cites the Handbook of Mineralogy, a university geology page, the USGS or a state survey.
Show all 66 entries
| Name | Type | Mohs hardness | Streak | Quick test |
|---|---|---|---|---|
| Agate (banded chalcedony) | mineral | 6.5 to 7 | white | Hold a flashlight behind a thin edge. Agate glows; jasper stays dark. |
| Amethyst (purple quartz) | mineral | 7 | white | Scratch test on glass: amethyst scratches it, fluorite does not. |
| Apatite | mineral | 5 | white | Knife test, then a glass test. |
| Augite (pyroxene) | mineral | 5 to 6 | white, green | Compare the cleavage angles with a hand lens. |
| Azurite | mineral | 3.5 to 4 | blue | Streak test. |
| Barite | mineral | 3 to 3.5 | white | Heft it next to a similar-sized rock, then try vinegar. |
| Basalt | rock | varies | n/a | Look with a lens for tiny grains, bubbles or green olivine specks. |
| Beryl (emerald, aquamarine) | mineral | 7.5 to 8 | white | Check the crystal ends, then a scratch test against quartz. |
| Biotite (black mica) | mineral | 2.5 to 3 | white, brown | Lift a flake with a pin or fingernail. |
| Black tourmaline (schorl) | mineral | 7 to 7.5 | white | Look at the end of a crystal and try a glass scratch test. |
| Calcite | mineral | 3 | white | Put a drop of vinegar on it and watch for bubbles. |
| Chalcopyrite | mineral | 3.5 to 4 | green-black | Knife test: chalcopyrite scratches, pyrite does not. |
| Chert and flint | rock | 7 | white | Scratch glass and look for curved (conchoidal) break surfaces. |
| Chrysocolla | mineral | 2 to 4 | white | Scratch test: often soft enough for a coin or knife. |
| Coal | rock | varies | n/a | Look for bright and dull bands along the side. |
| Common opal | mineraloid | 5.5 to 6.5 | white | Compare with quartz: opal only just scratches glass. |
| Conglomerate | rock | varies | n/a | Look at the pebble edges: rounded or angular? |
| Corundum (ruby and sapphire) | mineral | 9 | white | Try to scratch topaz or quartz with it. |
| Diorite | rock | 5 to 6.5 (est.) | n/a | Look with a lens: white feldspar and black hornblende. |
| Dolomite | mineral | 3.5 to 4 | white | Scratch with a copper coin: calcite scratches, dolomite resists. |
| Fluorite | mineral | 4 | white | Scratch with a coin, then with a knife. |
| Gabbro | rock | 5.5 to 6.5 (est.) | n/a | Look with a lens for dark pyroxene and gray feldspar grains. |
| Galena | mineral | 2.5 to 2.75 | gray-black | Heft it, then streak it. Wash your hands afterwards: it is a lead mineral. |
| Garnet | mineral | 6.5 to 7.5 | white | Scratch glass and count the crystal faces. |
| Gneiss | rock | varies | n/a | Look for alternating light and dark mineral bands. |
| Goethite (rusty limonite) | mineral | 5 to 5.5 | yellow-brown | Streak test. |
| Granite | rock | 6 to 7 (est.) | n/a | Look with a lens for the three grain types. |
| Graphite | mineral | 1 to 2 | gray-black | Rub it on white paper. |
| Gypsum and selenite | mineral | 1.5 to 2 | white | Fingernail scratch test. |
| Halite (rock salt) | mineral | 2 to 2.5 | white | Drop a small chip in water and see if it dissolves. |
| Hematite | mineral | 5 to 6 | red-brown | Streak test on the back of a white tile. |
| Hornblende | mineral | 5 to 6 | green | Streak test on a tile. |
| Iron meteorite | meteorite | varies | n/a | Run the meteorite checker, then ask an expert before paying for tests. |
| Jasper | mineral | 6.5 to 7 | white | Flashlight test on a thin edge, then a glass scratch test. |
| Limestone | rock | 3 to 4 (est.) | white | Vinegar drop test. |
| Magnetite | mineral | 5.5 to 6.5 | gray-black | Magnet test, then streak. Magnetic plus a dark streak points to magnetite, not a meteorite. |
| Malachite | mineral | 3.5 to 4 | green | Streak test, then look for bands on a broken face. |
| Marble | rock | 3 to 4 (est.) | white | Vinegar test and knife test. Quartzite fails both. |
| Muscovite (white mica) | mineral | 2 to 2.5 | white | Try to peel a flake with a fingernail. |
| Native copper | mineral | 2.5 to 3 | n/a | Scratch a hidden spot and look for a fresh copper shine. |
| Native gold | mineral | 2.5 to 3 | n/a | Press a pin into it: gold dents, pyrite and mica flakes break. |
| Obsidian (volcanic glass) | rock | varies | n/a | Look at a broken edge with a lens: only smooth glass. Handle edges carefully. |
| Olivine (peridot) | mineral | 6.5 to 7 | white | Scratch glass and look at the grains with a lens. |
| Petrified wood | fossil | 6.5 to 7 (est.) | white | Look at the end for growth rings, then try a glass scratch test. |
| Plagioclase feldspar | mineral | 6 to 6.5 | white | Tilt a flat face under a lamp and look for fine parallel lines with a lens. |
| Potassium feldspar (orthoclase) | mineral | 6 to 6.5 | white | Scratch glass (it just does) and look for flat, shiny breaks. |
| Pumice | rock | varies | n/a | Drop it in a glass of water. |
| Pyrite (fool's gold) | mineral | 6 to 6.5 | green-black, gray-black | Streak test on a white tile. |
| Quartz | mineral | 7 | white | Try to scratch glass with a sharp edge. Quartz scratches it; calcite and glass do not. |
| Quartzite | rock | 7 (est.) | white | Scratch glass, then try vinegar. |
| Rhodochrosite | mineral | 3.5 to 4 | white | Knife scratch test: rose quartz resists, rhodochrosite scratches. |
| Rhyolite | rock | varies | n/a | Look with a lens for flow bands and scattered small crystals. |
| Rose quartz | mineral | 7 | white | Scratch glass with it. Pink calcite and rhodochrosite are far softer. |
| Sandstone | rock | varies | n/a | Rub it: loose grains may come off on your fingers. |
| Schist | rock | varies | n/a | Look for mica flakes and garnet crystals with a lens. |
| Scoria (lava rock) | rock | varies | n/a | Compare with pumice in water: pumice usually floats, scoria is denser. |
| Serpentine | mineral | 2.5 to 3.5 | white | Coin or knife scratch test. |
| Shale and mudstone | rock | varies | n/a | Tap it: shale gives a dull thud where slate rings. |
| Slag (man-made) | man-made | varies | n/a | Look for bubbles and glass. Slag is common in fill, gravel and near old industry. |
| Slate | rock | varies | n/a | Tap it: slate rings, shale thuds. |
| Sodalite | mineral | 5.5 to 6 | white | Streak test: white suggests sodalite, bright blue suggests lapis. |
| Stony meteorite (chondrite) | meteorite | varies | white, gray-black | Run the meteorite checker. Look for the fusion crust first. |
| Sulfur | mineral | 1.5 to 2.5 | white | Fingernail test. Keep it away from flames. |
| Talc | mineral | 1 | white | Fingernail test: it scratches easily and leaves powder. |
| Topaz | mineral | 8 | white | See whether it scratches a quartz crystal. |
| Turquoise | mineral | 5 to 6 | white, blue | Streak test and a careful knife test on a hidden spot. |
Questions
How do I identify a rock I found?
Test what you can at home: hardness with a fingernail, a copper coin, a steel knife and glass; streak on the back of a white tile; luster under a lamp; and a magnet and a drop of vinegar. The rock identifier turns those answers into a ranked list of likely candidates.
Is this rock identifier free?
Yes. It is free, needs no account and runs in your browser. It asks questions instead of taking a photo, so nothing is uploaded.
Can a rock identifier be wrong?
Yes. Many minerals share colors and rocks are mixtures, so any quiz or photo tool can be wrong. Treat the results as likely candidates and confirm the top one with the test it suggests.
What is the most reliable test for identifying minerals?
Hardness and streak. Color is the least reliable, because the same mineral can come in many colors while its hardness and streak stay nearly the same.
How do I know if my rock is valuable?
First find out what it is, then compare it with sold listings or ask a rock club, a reputable dealer or an appraiser. Most common rocks are worth little in money, but rare minerals, fine crystals, gold and meteorites can be.
Guides that go with this
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How to Identify Rocks: A Simple 7-Test Method
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Rock Identification Chart: Match Your Find in 5 Steps
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Streak Test: What Your Rock's Streak Color Means
