What Kind of Rock Is This?
Found a rock and want to know what it is? Upload a photo and our identifier names the most likely rock in seconds, tells you how confident it is, and shows you the simple tests to confirm it — and it says so when it isn't sure.
The three families of rock
Almost every rock falls into one of three groups — placing yours is the first step:
- Igneous — cooled from molten rock; interlocking crystals or a glassy/bubbly texture. Granite, basalt, obsidian, pumice.
- Sedimentary — compacted grains or layers, often with fossils. Sandstone, limestone, shale, conglomerate.
- Metamorphic — reshaped by heat and pressure, often banded or foliated. Gneiss, schist, slate, marble, quartzite.
Want the full method? Read the rock identification guide.
A quick rock key: answer these in order
Geologists narrow a rock down with yes-or-no questions. Work down the list and stop at the first question you can answer yes to:
1. Is it glassy, with no grains at all?
Volcanic glass cools too fast for crystals to grow. It breaks with smooth, curved, shell-like edges.
Likely: Obsidian
2. Is it full of gas bubbles?
Pale and light enough to float usually means pumice. Dark, heavier and bubbly is scoria, a frothy form of basalt.
3. Can you see interlocking crystals by eye?
Light and speckled, often pink or white with black flecks, points to granite. Evenly salt-and-pepper suggests diorite. Dark and coarse suggests gabbro.
4. Is it fine-grained, with crystals too small to see?
Dark gray to black is most often basalt, the commonest volcanic rock on Earth. Medium gray with scattered larger crystals leans andesite; pale pink or gray leans rhyolite.
5. Does a drop of vinegar fizz on it?
Fizzing means calcium carbonate. Grainy or fossil-flecked is limestone, sugary and crystalline is marble, and banded with small holes is travertine.
Likely: Limestone, Marble, Travertine
6. Is it built from grains, pebbles or layers?
Gritty like sandpaper is sandstone. Rounded pebbles cemented together make conglomerate; sharp, angular chunks make breccia. Very fine, smooth layers are mudstone or siltstone.
Likely: Sandstone, Conglomerate, Breccia, Mudstone, Siltstone
7. Does it split into sheets or show stripes?
Thin, smooth sheets like roof tiles are slate. Glittering with flakes of mica is schist. Alternating light and dark bands are gneiss.
8. Is it very hard, with no fizz and no layers?
Sugary, glittering and hard enough to scratch glass is quartzite. Smooth and waxy, breaking with curved edges, is chert or flint.
Is it even a rock?
A surprising share of mystery finds are man-made. Rule these out before going further:
- Slag: glassy or metallic, often full of bubbles and streaked with rusty or bright colors — waste from old furnaces, common near railroads and old industrial sites.
- Concrete: small pebbles set in gray cement, often with one flat, straight edge.
- Brick: uniform orange-red or yellow clay, sometimes with a molded face or straight corners.
- Glass: smooth, often frosted from tumbling in water, with no grains inside — beach glass is old bottle glass.
Think it fell from space? Most suspected meteorites turn out to be earthly — slag, hematite or magnetite. The checks that tell them apart are in how to identify a meteorite.
How to photograph it for the best result
- Shoot in daylight against a plain background, filling the frame with the rock.
- Show a freshly broken or cut surface if you can — weathered outsides hide the real colour and grain.
- Include something for scale, and capture any layers, grains or crystals up close.
How to confirm what you found
A photo gets you most of the way; these quick tests settle the rest:
- Hardness: can it scratch glass (hard, ~6+) or does a knife scratch it (softer)?
- Acid fizz: a drop of vinegar fizzes on limestone and marble (carbonates), not on granite or sandstone.
- Streak & grain: rub it on unglazed tile for its true powder colour, and look closely for grains, layers or crystals.
Frequently asked questions
How can I tell what kind of rock I have?
Start with a clear, well-lit photo and our AI will name the most likely rock and how confident it is. Then confirm with a few quick checks: how hard it is (does it scratch glass?), its streak color on unglazed tile, whether it fizzes with vinegar, and whether you can see grains, layers or crystals. Those four tests separate most common rocks.
Can AI really tell what kind of rock this is from a photo?
For many specimens, yes — colour, grain size, texture and layering are often enough to place a rock. But some rocks look almost identical in a photo, so we give you a confidence score and the at-home tests to confirm, instead of a confident guess that might be wrong.
What are the three main types of rock?
Igneous (cooled from molten rock — e.g. granite, basalt), sedimentary (compacted layers or grains — e.g. sandstone, limestone), and metamorphic (changed by heat and pressure — e.g. gneiss, schist, marble). Spotting which family a rock belongs to is the first step in identifying it.
Can Google identify rocks?
Google Lens can show you photos that look like your rock, which is a useful start. It doesn't tell you how sure it is, doesn't weigh look-alikes against each other, and can't suggest the physical checks — hardness, streak, a vinegar fizz — that settle many rocks. This identifier names a best match, gives a confidence score and tells you which test confirms it.
What is this rock worth?
Most everyday rocks — granite, basalt, sandstone, limestone — have little cash value, however striking they look. The money is in gem-quality crystals, genuine meteorites, some fossils and fine mineral specimens. Identify it first: Pro adds a value-and-rarity report to each identification.
Is it free?
Yes — your first 3 identifications are free, with confidence scores and how-to-confirm tips on every result.
Looking for a crystal or gemstone instead? Try the crystal identifier or browse the field guide.