Identify a rock from a photo or a step-by-step key

A rock identifier reads what a photo carries: color, grain, luster and shape. The key below reads what a photo cannot — hardness, fizz and how the rock breaks. Answer four questions about the stone in your hand and it ends on named candidates, each with the physical test that confirms it.

What kind of rock is this: work the key

The key asks about four properties, in the order that eliminates the most candidates: grain, layering, hardness against a steel nail, and whether vinegar fizzes. Answer from a fresh face — break a corner off or wet the stone first, because a weathered rind hides every one of them. Nothing here needs a phone: the key runs in the page, and it needs no photo, no upload and no account.

Step 1
What is the first thing you notice about the surface?
Work from a fresh face. Wet the stone or break a corner off first — a weathered rind hides grain, color and every test below.
Step 2
Glass and froth: how heavy is it, and how does it break?
Step 3
Layers and sheets: do the split faces glitter?
Step 4
Dull sedimentary beds: what are the layers made of?
A steel nail sits near 5.5 on the Mohs scale and a fingernail near 2.5, so what scratches what places the rock in a band. Keep the vinegar for the last option.
Step 5
Visible grains, no layers: how do the grains fit together?
Step 6
Too fine to see grains: put a drop of household vinegar on a fresh scratch.
Scratch first. Vinegar reacts with fresh carbonate powder and often does nothing visible on a weathered surface, which is the most common false negative in this test.
Step 7
Glittering or silky split faces: how coarse are the flakes?
Step 8
Vinegar and a steel nail on a fresh face.
This pair separates the three pale rocks that people mix up most often. Run both tests before deciding — either one alone leaves two candidates standing.

Start over

Two tools cover the whole key: a steel nail and a bottle of household vinegar. A copper coin and a glass bottle sharpen the hardness answer, and the rock identification chart is the same twenty rocks laid out as a lookup table when you would rather browse properties than answer questions.

Where the key lands and how to confirm it

Every branch of the key ends in this table, and every row names a test rather than a feeling. That is the part most identifiers skip: a bare label is a claim you cannot check, while “it fizzes in vinegar and a copper coin marks it” is one you can settle in a minute at the kitchen sink. The last column matters just as much — it tells you what the answer becomes when the check comes back wrong.

Candidate	The check that confirms it	If the check fails
Obsidian	A fresh break is a smooth curved hollow with glass-sharp edges, and there are no round bubbles anywhere inside.	Round bubbles mean slag or bottle glass, not obsidian; a grainy break means it is not glass at all, so restart at step 1.
Pumice	Drop it in a bowl of water. Pumice floats, and no other common rock does.	It sinks and feels heavy for its size: read the scoria row instead.
Scoria	It sinks, feels dense in the hand, and the holes are rounded gas bubbles rather than gaps between grains.	It floats, so it is pumice. The holes are angular gaps between visible grains, so restart at step 1.
Gneiss	The light and dark bands are contorted rather than flat, and the rock will not part along them however hard you try.	It splits along the banding: go back to step 3 and take the glittering branch.
Sandstone	Rub a fresh face hard with a thumb and individual sand grains come away. Under a lens the grains are rounded and separated by cement.	Nothing rubs off and a steel nail leaves no mark: test for quartzite at step 8, where a break cuts through grains instead of around them.
Conglomerate	The pebbles are rounded, of mixed rock types, and sit in a cement of visibly different color and texture.	The fragments are angular with sharp corners: read the breccia row.
Breccia	The fragments have sharp corners and unworn edges, which is what tells you they were never carried far by water.	The fragments are rounded and smooth: read the conglomerate row.
Shale	It splits into flat sheets, a fingernail scratches it, and a damp face gives a distinct earthy clay smell.	No smell, harder, and the plates ring when tapped: it is slate, the metamorphosed version of the same mud.
Limestone	Vinegar fizzes visibly on a fresh scratch and a copper coin marks the surface, because calcite sits at 3 on the Mohs scale.	No fizz and the coin leaves nothing: it is chert or quartzite, both of which will scratch glass.
Granite	Pick out three different minerals with a hand lens — glassy quartz, blocky pale feldspar, dark flecks of mica or hornblende — locked together with no cement between them.	The pale grains are rounded and rub off under a thumb: it is sandstone.
Gabbro	Crystals are coarse enough to see, dark all the way through, and the piece is noticeably heavier than a granite of the same size.	The rock is dark but you cannot see individual crystals: it is basalt, the fast-cooled version.
Basalt	Fine-grained, dark, heavy, silent in vinegar, and many basalts tug faintly at a strong magnet because of the magnetite they carry.	It fizzes: it is limestone. It has no grain at all and breaks like glass: go back to step 2.
Chert or flint	It scratches a glass bottle, breaks in curved shells, and feels waxy rather than gritty. Struck hard against steel, the flint variety throws sparks.	A steel nail scratches it: it is not chert. Go back to step 6 and try the earthy branch.
Mudstone	A fingernail or a steel nail scratches it easily, it breaks into blocky lumps rather than sheets, and wetting brings out a clay smell.	It splits into flat sheets instead of blocks: it is shale, its layered twin.
Slate	It splits into flat plates with a dull sheen, and a thin plate rings rather than thuds when tapped against a hard edge.	The sheets are wavy and sparkle with countable flakes: it is schist.
Phyllite	The sheen is silky and the surface slightly crinkled, yet you still cannot pick out a single mica flake with the naked eye.	Countable flakes make it schist; dead-flat dull plates make it slate.
Schist	Mica flakes are large enough to count, they all lie the same way, and the rock splits along them into wavy glittering sheets.	The light and dark minerals form straight bands you cannot split: it is gneiss.
Marble	Vinegar fizzes on a fresh scratch and a copper coin marks it, yet the grains are sugary and interlocking rather than dull and muddy.	Sugary but silent in vinegar and untouched by the nail: it is quartzite.
Quartzite	It scratches a glass bottle, a steel nail leaves nothing, vinegar does nothing, and a broken face cuts through the grains instead of around them.	It fizzes: it is marble. Grains rub off under a thumb: it is sandstone.

The checks the key asks you to run

All of them use things already in the house, and together they separate most common lookalikes. The hardness kit is calibrated against the Mohs scale in the chart linked above; the powder test gets a page of its own in the streak test.

Check	Tool	What the result means
Hardness	Fingernail, copper coin, steel nail	A fingernail is about 2.5 on the Mohs scale, a steel nail about 5.5, quartz is 7. What scratches what places the stone in one of three bands.
Streak	Unglazed tile or the bottom of a mug	The powder color often differs from the stone: pyrite streaks greenish black, hematite streaks red brown regardless of its surface color.
Fizz	Household vinegar	Carbonates react. Limestone and marble fizz where quartzite stays silent — the fastest split of that pair there is.
Float	A bowl of water	Pumice floats and nothing else common does. It settles the one branch of the key where two rocks look identical and weigh nothing alike.

What a photo can and cannot settle

A photo carries color, grain size, luster, shape and surface texture. That resolves obsidian, pumice, conglomerate, banded agate and most of the distinctive igneous rocks on sight. It does not carry hardness, density, streak or the interior of the stone, and those are exactly the properties that separate the gray lookalikes. The USGS puts it plainly: rocks are extremely difficult to identify from photographs and want examining in person, from every side.

A photo is evidence, not a verdict. The honest output of any identifier is a shortlist plus the one test that decides it.

This is also why a stone that might be worth money deserves more than an app’s opinion. If the question is not just what is it but is it worth anything, work through how to identify valuable rocks before spending on an appraisal — most candidates eliminate themselves at the kitchen table.

How photo rock identification works

The app compares your photo against learned examples of rocks photographed in ordinary conditions: beach finds, garden gravel, trail cuts, broken faces. What comes back is a short ranked list, because that is what the evidence supports. A photograph narrows hundreds of possibilities down to two or three — and rarely enough to justify exactly one.

Step 1Photograph the stoneDaylight, plain background, stone filling the frame. Dry first, then wet — wetting reveals banding and grain that dust hides.
Step 2Read the ranked matchesTwo or three candidates with photos of each, not a single take-it-or-leave-it label. Ties are shown as ties.
Step 3Run the deciding checkEach match lists the property that separates it from its lookalike: hardness, streak, fizz or weight in the hand.
Step 4Save the findLocation, date and the confirmed name go into your collection log, so a summer of beach finds stays organized.

What comes back with each match

A bare name is not an identification — it is a claim you cannot check. Every match ships with the evidence you would need to argue with it, which is the same discipline the key above follows.

The properties behind the nameHardness range, streak color, luster and typical grain, so you can compare the claim against the stone rather than trust the pixels.

The usual impostorEvery common rock has one: quartzite passes for marble, basalt for gabbro, slag for meteorite. The match names its impostor and the test that splits them.

Where it tends to turn upA rock that does not occur within five hundred miles of the beach you are standing on is probably not what the photo suggests. Context filters bad answers.

If your find is a pointed cluster or a tumbled purple stone, start with the crystal identifier instead — crystals fail and pass different checks than rocks do, and that key asks about habit and color rather than grain. A faceted or polished stone from jewelry belongs with the gem identifier, where the honest limits are stricter.

Free online identifiers vs the app

Browser-based photo identifiers exist and some are decent at the shortlist step. The difference is what happens after the upload.

Gleamite appCamera-first, works on the beach without signal, keeps a collection log, and pairs every match with the check that confirms it.

Free web identifiersFine for a one-off upload at a desk. No offline use, no log, and most return a single name with no way to check it against the stone.

If you want the comparison done properly — including the apps we compete with, by name — the rock identifier app comparison lays out what each one verifiably offers. For minerals rather than rocks, the mineral identification chart sorts by luster, hardness and streak instead.

Questions people ask

What kind of rock is this?

Four properties answer it for almost every find: grain size, whether the rock is layered, whether a steel nail scratches it, and whether vinegar fizzes on a fresh scratch. The key on this page asks those four in order and ends on a named candidate with the test that confirms it.

How accurate are rock identifier apps?

Accurate enough to shortlist, not to certify. Distinctive rocks such as obsidian or banded agate resolve reliably; fine-grained gray rocks often return several plausible candidates. No vendor publishes a tested accuracy figure, so treat any single-name answer as a hypothesis and confirm it with a hardness or streak check.

What is the best free way to identify a rock?

Work a key with three household tools: a steel nail for hardness, an unglazed tile for streak, and vinegar for carbonate fizz. That costs nothing and it is what the key on this page automates. A photo tool shortens the shortlist first, which turns an evening of guessing into about ten minutes of checking.

Can a rock be identified from a photo alone?

Sometimes. A photo carries color, grain size, luster and shape, which is enough for distinctive rocks like pumice or conglomerate. It cannot carry hardness, density or streak, so lookalike pairs such as quartzite and marble need one physical test to separate — which is why every result here lists the deciding check.

Why do different apps name the same rock differently?

Because each model is trained on different images and a photograph underdetermines the answer. Two apps can both be reasonable and disagree, especially on fine-grained rocks. The disagreement itself is information: the candidates they share are worth testing first, and a streak or hardness check usually picks the winner.

What photo works best for rock identification?

Daylight, no shadows, the stone filling most of the frame, on a plain background. Shoot it dry first, then wet: wetting reveals banding and grain that dust hides. Add one photo of a freshly exposed face if you can — weathered crusts are the most common reason an identification goes wrong.

Sources

The query rock identifier draws 5,700 US searches a month at keyword difficulty 28; what kind of rock is this draws 2,400 at difficulty 31 and what kind of stone is this 1,000 at difficulty 0 — Ahrefs Keywords Explorer, US, 2026 · checked 2026-09-01
USGS states that rocks and minerals are extremely difficult to identify from photographs and must be examined in person from all perspectives — which is why every result here carries a physical check — U.S. Geological Survey, Can you identify my rock or mineral?, 2026 · checked 2026-09-02
Quartz measures 7 on the Mohs scale; a steel nail sits near 5.5 and a fingernail near 2.5 — Geology.com, Mohs Hardness Scale, 2026 · checked 2026-08-18