🪨 AI-Powered Rock Identification

Rock Identifier —
What Rock Is This?

Upload a photo of any rock specimen — igneous, sedimentary, or metamorphic. Our AI identifies the rock type, explains how it formed, describes its mineral composition, and tells you where in the world it is commonly found. Free, no sign-up, results in seconds.

Free · No sign-up All three rock families Field specimens & outcrops Economic uses included Results in seconds

What You Get in Every Result

Rock name and rock family — igneous, sedimentary, or metamorphic
Confidence percentage with detailed visual reasoning
Mineral composition — primary and accessory minerals
Texture and grain size description
How and where the rock formed geologically
Common global locations and geological settings
Economic and industrial uses
Similar rocks to check and how to distinguish them
Collector interest and field notes

Rock Identifier

Upload a photo of your rock or mineral and get an instant AI-powered identification.

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Description

How it Forms

Hardness (Mohs)

Luster

Rarity

Collector Value

Common Locations

Typical Colors

Key Properties

Similar Rocks

Alternative Identifications

Collection Tip

The Three Rock Families

Every rock on Earth belongs to one of three families — igneous, sedimentary, or metamorphic — each defined by how and where it formed. Identifying which family your specimen belongs to is always the first step, because each family has completely different diagnostic properties that guide the rest of the identification process.

Igneous Rocks

Formed from cooled magma or lava

Created when molten rock cools and solidifies — either deep underground (intrusive) or at the surface (extrusive). Characterised by interlocking crystals or volcanic glass. No fossils, no layering, no foliation.

GraniteBasalt ObsidianPumice RhyoliteGabbro AndesiteDiorite

Sedimentary Rocks

Formed from compressed sediments

Built up from layers of sediment — mineral particles, organic material, or chemical precipitates — compressed over millions of years. Characterised by visible layering, fossils, and rounded grains. The most common surface rocks.

SandstoneLimestone ShaleConglomerate CoalChalk FlintMudstone

Metamorphic Rocks

Formed by heat and pressure

Created when existing rocks are subjected to extreme heat, pressure, or both — transforming their mineral composition and texture without melting. Characterised by foliation (platy alignment), banding, or recrystallised fabric. Often sparkly.

MarbleSlate QuartziteSchist GneissPhyllite HornfelsEclogite

The rock cycle — why rocks transform

No rock type is permanent. Igneous rocks exposed at the surface weather into sediment, which compacts into sedimentary rock. Both igneous and sedimentary rocks can be buried and transformed by heat and pressure into metamorphic rock. Any rock type can be re-melted into magma, which then cools into new igneous rock. This continuous transformation — the rock cycle — means the same atoms that made up an ancient granite can today be part of a limestone on the ocean floor.

Common Rocks — Quick Identification Reference

These are the rocks most commonly encountered by field geologists, hikers, builders, and collectors. Understanding their key diagnostic properties helps you understand and verify the AI’s identification reasoning.

Rock	Family	Texture	Key Diagnostic Feature	Common Uses
Granite	Igneous	Coarse crystalline	Visible interlocking crystals of quartz, feldspar, and mica; speckled appearance	Building stone, countertops, monuments
Basalt	Igneous	Fine to aphanitic	Dark grey to black; very fine-grained; may show vesicles (gas holes)	Road aggregate, construction, columns
Obsidian	Igneous	Glassy (vitreous)	Jet black volcanic glass; conchoidal fracture with razor-sharp edges	Cutting tools, jewellery, blades
Pumice	Igneous	Vesicular (frothy)	Extremely light — floats on water; pale grey; countless gas bubble holes	Abrasive, cosmetics, lightweight concrete
Sandstone	Sedimentary	Clastic (granular)	Visible sand grains; gritty feel; may show cross-bedding; various colours	Building stone, flagging, glass production
Limestone	Sedimentary	Crystalline to bioclastic	Effervesces in dilute acid; often contains fossil fragments; grey to cream	Cement, lime, construction, agriculture
Shale	Sedimentary	Fine-grained fissile	Splits into thin flat layers; earthy smell when wet; grey, black, or red	Brick, ceramics, oil shale extraction
Conglomerate	Sedimentary	Coarse clastic	Large rounded pebbles cemented together; visually distinctive	Aggregate, decorative stone
Flint / Chert	Sedimentary	Microcrystalline	Very hard; dark grey to black; conchoidal fracture; waxy luster	Flintlock mechanisms, cutting tools, road fill
Marble	Metamorphic	Crystalline	Recrystallised calcite; sugary texture; effervesces in acid; various colours	Sculpture, flooring, countertops
Slate	Metamorphic	Fine-grained foliated	Splits into thin flat slabs; dull luster; dark grey to black or green	Roofing, flooring, blackboards, billiard tables
Quartzite	Metamorphic	Granoblastic	Very hard (7+); glassy fracture; grains fused — no individual grains visible; pale	Railway ballast, roofing tiles, flooring
Schist	Metamorphic	Foliated schistose	Parallel alignment of mica flakes; sparkly surface; visible flaky minerals	Decorative stone, aggregate
Gneiss	Metamorphic	Foliated banded	Alternating light and dark mineral bands (compositional banding); coarse-grained	Building stone, decorative facing panels

Rock Texture — The Most Diagnostic Visual Property

Texture is the single most important visual property for rock identification. It tells you how the rock formed, how fast it cooled or compressed, and which broad category it belongs to. Our AI analyses texture from your photograph as the primary diagnostic input.

Coarse-grained (Phaneritic)

Intrusive Igneous

Individual mineral crystals are large enough to see with the naked eye — typically 1mm or larger. Indicates slow cooling deep underground giving crystals time to grow. Granite, gabbro, and diorite are typical examples. The specific minerals visible and their proportions identify the rock type.

Fine-grained (Aphanitic)

Extrusive Igneous

Crystals are too small to see without a hand lens — rapid cooling at the surface prevented crystal growth. Basalt, rhyolite, and andesite are the common examples. Colour, vesicles, and any phenocrysts (larger crystals set in fine groundmass) are the key identifiers.

Glassy (Vitreous)

Extrusive Igneous

No crystalline structure at all — lava cooled so rapidly that atoms had no time to organise into crystals. Obsidian is the classic example. Characteristic conchoidal fracture and vitreous (glassy) luster are unmistakable. Pumice is a glassy rock inflated with gas bubbles.

Porphyritic

Igneous (both)

Large crystals (phenocrysts) set within a finer groundmass — indicating two-stage cooling history. The magma cooled slowly at depth (growing phenocrysts) then erupted and cooled rapidly (creating the fine matrix). Common in andesite and porphyritic granite.

Clastic (Fragmental)

Sedimentary

Built from fragments of pre-existing rock — grains, pebbles, or clay particles cemented together. Grain size defines the rock: gravel → conglomerate, sand → sandstone, silt → siltstone, clay → shale/mudstone. Rounding of grains indicates transport distance.

Bioclastic / Fossiliferous

Sedimentary

Composed largely of fossil fragments — shells, coral, bone, or plant material. Limestone is the most common example. Fossils are exclusively found in sedimentary rocks — their presence immediately confirms the rock family and often helps establish geological age.

Foliated (Schistose/Slaty)

Metamorphic

Minerals have been aligned into parallel planes by directional pressure — the rock splits preferentially along these planes. Slaty cleavage (slate) is fine-grained and dull. Schistosity (schist) shows visible mica flakes. Gneissic banding shows alternating compositional layers.

Non-foliated (Granoblastic)

Metamorphic

Recrystallised without directional pressure, so no planar fabric develops. Marble (recrystallised limestone) and quartzite (recrystallised sandstone) are classic examples. These rocks show interlocking recrystallised grains with no preferred orientation.

“Texture answers the question ‘how did this rock form?’ before you even know what minerals it contains. A coarse-grained interlocking fabric means slow cooling at depth — that eliminates every sedimentary and most metamorphic rock in one observation. Texture is always the first diagnostic step.”

How to Identify a Rock — A Systematic Approach

Professional geologists follow a systematic sequence when identifying rocks in the field. Understanding this sequence helps you provide the most useful context to our AI and interpret your result correctly.

Step 1 — Determine the rock family. Is it igneous, sedimentary, or metamorphic? Look for: interlocking crystals (igneous), visible layers or fossils (sedimentary), or foliation and recrystallised fabric (metamorphic). This single decision narrows thousands of rock types to a manageable subset.
Step 2 — Assess grain size and texture. Can you see individual grains or crystals with the naked eye? Are they the same size throughout, or are large crystals set in a fine groundmass? Does the rock split easily along flat planes? Each answer points toward specific rock types.
Step 3 — Identify visible minerals. What colours are visible? Shiny black flakes indicate biotite or hornblende. Pink or white blocky crystals indicate feldspar. Grey glassy grains indicate quartz. Silvery or golden flakes indicate mica. Even an approximate mineral inventory dramatically narrows the possibilities.
Step 4 — Check for special features. Fossils or shell fragments confirm sedimentary origin. Gas bubbles (vesicles) confirm volcanic origin. Shiny slickensides (polished fault surfaces) indicate tectonic movement. Reaction to acid (fizzing) confirms calcite content — limestone or marble.
Step 5 — Consider geological context. Where did you find this rock? A dark fine-grained rock from a volcanic island is almost certainly basalt. A pale coarse-grained rock from the core of a mountain range is almost certainly granite. A rock from a river pebble deposit could be anything — but the local geology constrains the possibilities strongly.

The acid test — fastest single confirmation for limestone and marble

A drop of dilute hydrochloric acid (or even household white vinegar) placed on a rock surface produces vigorous fizzing if the rock contains calcite — confirming limestone, chalk, or marble immediately. Dolomite reacts more slowly and only when powdered. This simple test takes seconds and definitively separates carbonate rocks from silicates. If you have already performed this test, mention the result in the context field for a significantly sharper identification.

Rocks vs Minerals — An Important Distinction

These two terms are often used interchangeably in everyday language but have precise scientific meanings that matter for identification purposes.

A mineral is a naturally occurring inorganic solid with a defined chemical composition and crystal structure. Quartz is a mineral — its composition is always SiO₂. Calcite is a mineral — always CaCO₃. Each mineral has specific, consistent physical properties.

A rock is an aggregate of one or more minerals. Granite is a rock composed of three minerals — quartz, feldspar, and mica — in varying proportions. Limestone is a rock composed primarily of the mineral calcite. Because rocks are mixtures, their properties vary between specimens — there is no single hardness or density for “granite” the way there is for quartz.

When to use Rock Identifier vs Mineral Identifier

Use Rock Identifier when your specimen is clearly a piece of rock — multiple minerals visible together, a hand-sized chunk from an outcrop, a river pebble, a building stone. Use Mineral Identifier when your specimen is a single mineral crystal or grain — an isolated cube of pyrite, a clear quartz point, a piece of malachite. If you are unsure, Rock Identifier handles both well and will direct you to the Mineral Identifier if the specimen appears to be a single mineral species.

Rocks With Gemstones Inside

Some rocks are primarily valuable because of the minerals or gemstones they contain rather than the rock itself. A piece of granite is a rock; the tourmaline crystal growing inside it is the mineral. A piece of kimberlite is the rock; the diamond it may contain is the mineral. Our rock identification result always notes when a rock type is commonly associated with gemstone minerals — and links you to the relevant specialist identifier tool.

Kimberlite and lamproite — the host rocks of diamond
Pegmatite — coarse-grained granite associated with tourmaline, topaz, beryl, spodumene, and rare minerals
Skarn — metamorphic rock associated with garnet, diopside, and sometimes ruby and sapphire
Marble — the host rock of many rubies and sapphires in classic Asian deposits
Basalt and rhyolite cavities — where agate, amethyst, and zeolite minerals crystallise
Serpentinite — the host rock of jade (nephrite), chromite, and platinum group metals

How to Photograph Rocks for Best Identification Results

Rock identification from photographs is most accurate when the images show the specific features the AI uses to determine rock type. These four tips make a consistent difference:

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Use raking light for texture

A single directional light source at a low angle across the surface reveals grain size, foliation planes, crystal faces, and surface texture far more clearly than overhead or flash lighting. Even a phone torch held at a low angle works well. This is the most important technique for igneous and metamorphic rocks.

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Photograph a fresh break if possible

The weathered exterior of a rock often looks very different from its fresh interior. If you can safely break a small piece, photograph the fresh face — it reveals true colour, grain size, mineral composition, and texture far more clearly than a weathered surface covered in oxidation and soil.

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Wet the surface

Wetting a rock surface dramatically enhances colour contrast and reveals mineral grains, banding, and texture that are invisible when dry. Field geologists routinely lick rocks to assess colour — wetting with water achieves the same result. The AI identifies wet specimens just as accurately as dry ones.

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Include a scale reference

Grain size is one of the most diagnostic rock properties — but it is only assessable if you can see how large the grains are relative to something known. A coin, pencil, or ruler placed beside the specimen allows the AI to calibrate grain size accurately. This is particularly important for distinguishing coarse from medium from fine-grained rocks.

Frequently Asked Questions

What is the difference between igneous, sedimentary, and metamorphic rocks?

The three rock families are defined by their formation process. Igneous rocks form when magma or lava cools and solidifies — either deep underground (intrusive, like granite) or at the surface (extrusive, like basalt). Sedimentary rocks form from layers of sediment — mineral particles, biological material, or chemical precipitates — compressed over time. Limestone, sandstone, and shale are sedimentary. Metamorphic rocks form when existing rocks are changed by extreme heat, pressure, or both — marble is metamorphosed limestone; quartzite is metamorphosed sandstone.

How do I tell granite from other coarse-grained rocks?

Granite is specifically defined by its mineral composition: it must contain quartz (grey, glassy), alkali feldspar (usually pink or white), and typically some mica (black biotite or silvery muscovite). The key is the presence of visible quartz — grey, glassy, irregular grains. Without quartz, a coarse-grained rock may be diorite (no quartz, darker overall) or gabbro (dark minerals dominant, very little quartz). The pink or salmon colour in many granites comes from potassium feldspar and is a useful field clue.

Can rocks contain fossils?

Fossils are found exclusively in sedimentary rocks. The conditions that preserve organic material — burial under sediment, gradual mineralisation, protection from high temperatures — exist only in the sedimentary environment. Igneous and metamorphic processes destroy organic material. The most fossil-rich rock types are limestone, shale, mudstone, and sandstone. Finding a fossil in a specimen immediately and definitively confirms it is sedimentary — one of the most useful single observations in field geology.

Why does my rock fizz when I put acid on it?

Fizzing in acid indicates the presence of calcite (calcium carbonate, CaCO₃). When acid contacts calcite, it releases carbon dioxide gas — producing the bubbles you see. Limestone fizzes strongly even in weak acid (vinegar). Marble also fizzes because it is recrystallised limestone. Dolomite (CaMg(CO₃)₂) fizzes only weakly and only when scratched first to produce powder. Silicate rocks like granite and basalt do not react with weak acids at all — so the presence or absence of fizzing immediately separates carbonate from silicate rocks.

What is obsidian and how does it form?

Obsidian is a volcanic glass — it forms when silica-rich lava (rhyolitic composition) cools so rapidly that atoms have no time to organise into crystals. The result is a natural glass with an entirely amorphous (non-crystalline) structure. It is typically jet black, sometimes with brownish or iridescent sheen, and breaks with a conchoidal fracture producing extremely sharp edges — sharper than surgical steel, which is why it was prized for blades by ancient cultures. Obsidian is found near relatively young volcanic centres worldwide.

Is pumice really light enough to float?

Yes — fresh pumice floats on water. Pumice is a frothy volcanic glass filled with countless tiny gas bubbles that formed when dissolved gases expanded as magma erupted explosively. The resulting foam solidified into a rock with so much air space that its bulk density is less than 1 g/cm³ — lighter than water. Pumice rafts covering hundreds of square kilometres of ocean surface have been documented after major submarine volcanic eruptions. Over time, water penetrates the pores and the pumice eventually sinks.

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