Rocks & minerals
What fossil is this?
Most fossils people find belong to about twenty groups, and shape sorts them fast: a coiled spiral, two matching halves, a stack of discs, a segmented shell, a branching structure, a tooth. The rock matters too — limestone, shale and chalk hold the great majority, and igneous rock holds none at all.
Narrow it down
Showing all 26 fossils
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Ammonite
A flat coil with chambers separated by walls, and where the shell has worn away the joins show as intricate fern-like suture lines. Ribs usually run across the coil.
In the record 411–56 Ma · from the Lochkovian · 94,365 catalogued occurrences check on PBDB
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Nautiloid and orthocone
Either coiled or a long straight cone, divided into chambers by simple curved walls. The tube running through the chambers, the siphuncle, is often visible as a line down the middle.
In the record first recorded 304 Ma, still living · from the Kasimovian · 2,466 catalogued occurrences check on PBDB
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Belemnite
A solid bullet-shaped rod of amber to dark brown calcite, often with a hollow cone at the wide end. Broken across, it shows radiating crystal fibres from a central line.
In the record 323–34 Ma · from the Visean · 2,108 catalogued occurrences check on PBDB
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Trilobite
Divided lengthwise into three lobes — hence the name — and crosswise into a head shield, a segmented body and a tail piece. Frequently found rolled into a ball, which is how it defended itself.
In the record 521–252 Ma · from the Fortunian · 55,973 catalogued occurrences check on PBDB
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Brachiopod
Two shells of <strong>unequal size</strong>, with a plane of symmetry running through the middle of each shell rather than between them. Many have a small hole at the beak where a fleshy stalk emerged.
In the record first recorded 526 Ma, still living · from the Fortunian · 187,697 catalogued occurrences check on PBDB
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Fossil bivalve
Two mirror-image shells of equal size joined at a hinge, exactly like a modern clam or oyster. Symmetry runs between the two shells, not through each one.
In the record first recorded 521 Ma, still living · from the Fortunian · 211,698 catalogued occurrences check on PBDB
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Devil's toenail
Gryphaea
A thick, heavily curved oyster shell that coils over on itself like a claw, with a small flat lid. Instantly recognisable and the source of its own folklore.
In the record 237–34 Ma · from the Ladinian · 1,214 catalogued occurrences check on PBDB
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Crinoid stem
Stacks of small discs, each with a central hole and often a star-shaped or radial pattern on the face, sometimes still joined into a column. Loose discs are the most abundant fossil in many limestones.
In the record first recorded 505 Ma, still living · from the Stage 4 · 14,526 catalogued occurrences check on PBDB
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Crinoid crown
A cup of plates with feathery arms radiating from it, on top of a stem. A complete crown is far rarer and far more valuable than loose stem discs.
In the record first recorded 505 Ma, still living · from the Stage 4 · 14,526 catalogued occurrences check on PBDB
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Horn coral
A curved cone shaped like a bull's horn, with radiating vertical partitions visible in the wide open end. A solitary rugose coral that lived on the sea floor.
In the record 471–7 Ma · from the Stage 10 · 16,723 catalogued occurrences check on PBDB
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Colonial and honeycomb coral
A mass of tightly packed tubes seen end-on as a honeycomb, or as long parallel tubes in section. Petoskey stone, Michigan's state stone, is a polished colonial coral.
In the record 477–252 Ma · from the Stage 10 · 11,856 catalogued occurrences check on PBDB
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Bryozoan
Delicate lacy nets, fine twigs or fan-shaped meshes covered in minute pores, each pore a separate animal. Often mistaken for coral, but the individual openings are far smaller.
In the record first recorded 515 Ma, still living · from the Stage 3 · 30,968 catalogued occurrences check on PBDB
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Fossil sea urchin
A dome or heart-shaped body with five bands of tiny paired pores radiating from the top in a flower pattern, and a surface covered in small bumps where the spines attached.
In the record first recorded 458 Ma, still living · from the Dapingian · 11,651 catalogued occurrences check on PBDB
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Shark tooth
A triangular enamel blade, usually glossy black or grey from mineral replacement, with a distinct root and often serrated edges. Megalodon teeth reach 18 cm and are unmistakable.
In the record first recorded 458 Ma, still living · from the Darriwilian · 27,309 catalogued occurrences check on PBDB
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Fossil fish
A complete skeleton laid flat in fine-grained rock, with the fin rays and the scale pattern often preserved. Green River fish are quarried commercially and are among the most affordable complete vertebrate fossils.
In the record first recorded 439 Ma, still living · from the Rhuddanian · 240,749 catalogued occurrences check on PBDB
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Dinosaur bone
Handle with careThe internal texture is the identification: bone shows a spongy honeycomb of cells with a denser outer wall, visible on any broken surface. Petrified wood shows growth rings and grain instead.
In the record first recorded 241 Ma, still living · 37,837 catalogued occurrences check on PBDB
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Petrified wood
Rock with the growth rings, bark texture and cell structure of wood preserved in silica, often brilliantly coloured by iron and manganese. Hard enough to scratch glass, and it takes a mirror polish.
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Fern and leaf impression
A flat black carbon film in the shape of a frond or leaf, splitting cleanly out of shale. Coal spoil heaps are the classic hunting ground and the detail can be extraordinary.
In the record first recorded 388 Ma, still living · from the Emsian · 19,372 catalogued occurrences check on PBDB
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Lepidodendron bark
A regular diamond or scale pattern covering the surface, each diamond a scar where a leaf was attached. A giant clubmoss up to 40 m tall, and one of the main sources of coal.
In the record 382–206 Ma · from the Givetian · 313 catalogued occurrences check on PBDB
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Calamites
A ribbed cylinder with regular joints across it, like a length of bamboo. A giant horsetail, related to the small ones still growing in ditches today.
In the record 319–171 Ma · from the Serpukhovian · 349 catalogued occurrences check on PBDB
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Stromatolite
Domed or columnar structures with fine concentric internal layers, built by mats of cyanobacteria trapping sediment. Some are 3.5 billion years old and are among the oldest evidence of life on Earth.
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Graptolite
Fine saw-blade or tuning-fork marks on dark shale, looking like pencil writing — the name means "written rock". Colonial floating animals, and precise markers for dating rock.
In the record 505–340 Ma · from the Stage 4 · 8,114 catalogued occurrences check on PBDB
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Coprolite
Fossilised dung: a lumpy irregular mass, often spiral or pinched at one end, sometimes containing bone fragments, scales or plant matter. Difficult to distinguish from a concretion without a section.
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Trace fossils and burrows
Vertical tubes, U-shaped burrows, ripple marks, trails and footprints. No body is preserved — the fossil is the behaviour, and for sedimentologists that is often more informative than a shell.
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Amber with inclusions
Handle with careFossilised tree resin, warm to the touch, floating in saturated salt water and picking up paper when rubbed. Insects and plant fragments trapped inside are preserved in three dimensions.
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Concretion — not a fossil
A hard rounded or lens-shaped lump that weathers out of softer rock, often with concentric internal layers. The source of most "fossil egg", "dinosaur bone" and "meteorite" reports.
Nothing in this key matches every filter at once. That usually means one observation is off — a colour read in shade, or a size guessed rather than measured. Clear the filter you are least sure about and look again.
The rock tells you what can be in it
Before looking at the object, look at what it is sitting in. That single observation eliminates most of the possibilities and tells you roughly how old it is.
- Limestone — the richest fossil rock there is, formed largely from shell and skeletal debris. Expect brachiopods, corals, crinoids, bryozoans, nautiloids. It fizzes in vinegar, which is how you confirm it.
- Shale and mudstone — fine sediment, so fine detail. Trilobites, graptolites, leaf and fern impressions, complete fish. Splits into flat sheets, and the fossil is usually on a bedding plane.
- Chalk — a very pure fine limestone. Echinoids, belemnites, sponges, occasional ammonites.
- Sandstone — higher energy, so mostly robust material and trace fossils. Footprints, burrows, petrified wood, dinosaur bone.
- Coal measures and their spoil heaps — Carboniferous plants, in extraordinary abundance.
- Igneous and most metamorphic rock — nothing. Granite, basalt and marble contain no fossils, because either the rock was molten or the recrystallisation destroyed them.
The corollary matters as much: a fossil found loose on a beach or in a gravel bar has lost its context. Where it came from is often unknowable, and for anything scientifically interesting the location and the bed are worth more than the specimen.
Six pairs people mix up
| Pair | The test |
|---|---|
| Ammonite vs nautiloid | Suture lines where the chamber walls meet the shell: frilled and fern-like in ammonites, simple curves in nautiloids |
| Brachiopod vs bivalve | Symmetry. A brachiopod's plane of symmetry runs through the middle of each shell and the two shells differ in size; a bivalve's runs between two mirror-image shells |
| Coral vs bryozoan | Aperture size. Coral corallites are millimetres across; bryozoan pores need a lens to see |
| Bone vs petrified wood | Internal texture on a broken surface: bone shows a spongy honeycomb with a dense outer wall, wood shows rings and grain |
| Fossil vs concretion | Concretions are structureless or concentrically layered inside. If a broken surface shows no biological structure, it is a concretion |
| Lepidodendron vs "dinosaur skin" | The regular geometric diamond pattern with a scar in each diamond is a fossil clubmoss trunk. Genuine skin impressions are irregular and very rare |
The suture line test deserves emphasis because ammonites are the most-found identifiable fossil in Europe and the sutures are visible on any specimen where the outer shell has worn off. Complex, frilled and repeating means ammonite; smooth arcs mean nautiloid, and nautiloids are much older.
Collecting legally
The rules differ sharply by country, by land ownership and — crucially — by whether the fossil is a vertebrate.
United States. On federal land the Paleontological Resources Preservation Act of 2009 allows casual collection of reasonable amounts of common invertebrate and plant fossils for personal use on most BLM and Forest Service land, and prohibits collecting vertebrate fossils entirely without a permit. National Parks prohibit all collecting. On private land, fossils belong to the landowner and you need permission.
United Kingdom. Most coastal fossil collecting is permitted under local codes; the Jurassic Coast has a published Fossil Collecting Code requiring significant finds to be recorded. Sites of Special Scientific Interest have their own restrictions, and hammering in situ is often prohibited even where collecting loose material is not.
Elsewhere. Many countries — including Italy, Portugal, Brazil, China, Mongolia and Morocco — prohibit export of fossils entirely. Buying a fossil abroad can mean carrying illegally exported material through customs.
Two universal rules. Collect loose material from scree, beach or spoil rather than hammering a face, which is both safer and less damaging. And record where it came from — the locality and the bed, ideally with a photograph in place. A fossil without provenance is an ornament; a fossil with it is data, and a museum can use it.
Where to find fossils, and how to do it safely
Fossils are where sedimentary rock is exposed and actively eroding, which in practice means a small number of settings.
- Coastal cliffs and the beach beneath them. The sea does the excavation for you. Go on a falling tide after a storm and work the loose material.
- Quarries and road cuts, with permission. Working quarries frequently allow organised group visits and nothing else.
- Stream beds and gravel bars, where flowing water concentrates hard material.
- Spoil heaps from old coal and mineral workings — the classic source of Carboniferous plant fossils.
- Ploughed fields on the right geology, after rain.
Safety is not a formality at cliff sites. Rockfall kills fossil collectors, and it happens without warning: never work directly beneath a cliff face, never dig into the base of a cliff, and check the tide times before you start. Being cut off by a rising tide under an unclimbable cliff is the other common way this goes wrong. Wear eye protection if you hammer at all, and a hard hat where there is any overhang.
When a find matters, and what to do about it
Amateur collectors have found a substantial share of important specimens — Mary Anning's ichthyosaur and plesiosaur, the Mazon Creek fauna, most known dinosaur trackways in the UK. What separates a scientifically useful find from a mantelpiece ornament is what happens in the first hour.
- Photograph it in place, with a scale, before touching it. Include a wider shot showing the bed and the surroundings.
- Record the location precisely. GPS coordinates, the bed, the date, the tide state if relevant.
- If it looks like vertebrate material — bone, teeth, articulated skeleton — stop and report it. Excavating a vertebrate fossil badly destroys most of its scientific value, and in the US on federal land it is also illegal.
- Contact a museum or a university geology department. They are consistently interested and consistently helpful, and in the UK the local Finds Liaison Officer or the Jurassic Coast Trust will advise.
26 entries here cover what people actually pick up and ask about. There are hundreds of thousands of described fossil species and a large proportion of any real collection cannot be taken beyond a group without expert help. Local geological societies run field trips and identification evenings, and they are by a wide margin the fastest way to learn a region's fossils.
How old the rock has to be
A fossil identification is only as good as the rock it came out of, and that is a fact you can check before you look at the specimen at all. Every group in this key is matched against the Paleobiology Database, which catalogues where and when each has actually been found: 989,814 recorded occurrences behind the 20 groups below, with a first and last appearance for each. The snapshot was taken on 2026-09-04.
The oldest group here is Brachiopod, first recorded 526 million years ago, and the best-evidenced is Fossil fish with 240,749 catalogued occurrences. The practical use of the chart is elimination: if the local rock is Cretaceous, anything whose bar has already ended cannot be in it, whatever the shape suggests. Local geological survey maps are free in most countries and will tell you the age of the outcrop you are standing on. Note also the 11groups that still have living members — Nautiloid and orthocone, Brachiopod, Fossil bivalve, Crinoid stem, Crinoid crown, Bryozoan, Fossil sea urchin, Shark tooth, Fossil fish, Dinosaur bone, Fern and leaf impression — because a specimen that looks like one of those is not automatically ancient, and beach-worn modern shell is the single most common thing mistaken for a fossil.
The reference table
First and last appearance in millions of years before present, the named stage at each end, and how many occurrences the database holds. A large occurrence count means the group is common in collections, which is a good proxy for how likely you are to find one.
| Group | First (Ma) | Last (Ma) | From | To | Occurrences | Still living |
|---|---|---|---|---|---|---|
| Brachiopod | 526 | 0 | Fortunian | present | 187,697 | yes |
| Trilobite | 521 | 252 | Fortunian | Changhsingian | 55,973 | no |
| Fossil bivalve | 521 | 0 | Fortunian | present | 211,698 | yes |
| Bryozoan | 515 | 0 | Stage 3 | present | 30,968 | yes |
| Crinoid stem | 505 | 0 | Stage 4 | present | 14,526 | yes |
| Crinoid crown | 505 | 0 | Stage 4 | present | 14,526 | yes |
| Graptolite | 505 | 340 | Stage 4 | Visean | 8,114 | no |
| Colonial and honeycomb coral | 477 | 252 | Stage 10 | Changhsingian | 11,856 | no |
| Horn coral | 471 | 7 | Stage 10 | Tortonian | 16,723 | no |
| Fossil sea urchin | 458 | 0 | Dapingian | present | 11,651 | yes |
| Shark tooth | 458 | 0 | Darriwilian | present | 27,309 | yes |
| Fossil fish | 439 | 0 | Rhuddanian | present | 240,749 | yes |
| Ammonite | 411 | 56 | Lochkovian | Thanetian | 94,365 | no |
| Fern and leaf impression | 388 | 0 | Emsian | present | 19,372 | yes |
| Lepidodendron bark | 382 | 206 | Givetian | Norian | 313 | no |
| Belemnite | 323 | 34 | Visean | Priabonian | 2,108 | no |
| Calamites | 319 | 171 | Serpukhovian | Aalenian | 349 | no |
| Nautiloid and orthocone | 304 | 0 | Kasimovian | present | 2,466 | yes |
| Dinosaur bone | 241 | 0 | — | present | 37,837 | yes |
| Devil's toenail | 237 | 34 | Ladinian | Priabonian | 1,214 | no |
Free to reuse with a link back to this page. The full snapshot behind every Orvik key is on the open field data page.
Questions people ask about this
How do I know if something is a fossil or just a rock?
Look for biological structure: symmetry, repeated segments, chambers, growth rings, a honeycomb texture, or a pattern that repeats regularly. Break or examine a fresh surface. Concretions — the source of most false alarms — are structureless or concentrically layered inside, and if a broken surface shows no biological pattern, that is what you have.
What is the difference between an ammonite and a nautiloid?
The suture lines, where the internal chamber walls meet the shell. In ammonites they are complex, frilled and fern-like; in nautiloids they are simple smooth curves. The lines are visible whenever the outer shell has worn away, which on beach specimens is most of the time. Nautiloids are also much older, appearing in the Palaeozoic, while ammonites dominate the Mesozoic.
Is it legal to collect fossils?
It depends on where and what. On US federal land, reasonable amounts of common invertebrate and plant fossils may be collected for personal use, and vertebrate fossils may not be collected at all without a permit; National Parks prohibit everything. Private land needs the owner's permission. In the UK most coastal collecting is permitted under local codes, with recording expected for significant finds. Several countries prohibit fossil export entirely.
What are those little discs with holes in the limestone?
Crinoid stem segments — sea lilies. Each disc is one plate from a long stalk that anchored a filter-feeding animal to the seabed, and they often show a star or radial pattern on the face. They are among the most abundant fossils in Palaeozoic limestone, and complete crowns with the arms attached are far rarer and far more valuable.
How can I tell fossil bone from petrified wood?
Look at the internal texture on a broken or cut surface. Bone shows a spongy honeycomb of cells surrounded by a denser outer wall. Petrified wood shows growth rings and a directional grain. Both can be beautifully coloured and both are hard enough to scratch glass, so colour and hardness will not separate them.
Where is the best place to look for fossils?
Anywhere sedimentary rock is exposed and actively eroding: coastal cliffs and the beach below them, stream beds and gravel bars, road cuts, quarry spoil and old mine heaps, and ploughed fields on the right geology. Falling tide after a storm is the best time on a coast. Igneous and most metamorphic rock contains nothing at all, so granite and basalt country is a waste of a day.
I think I found a dinosaur bone. What should I do?
Photograph it in place with a scale before touching it, record the location precisely, and contact a museum or university geology department rather than excavating it. Badly removed vertebrate material loses most of its scientific value, and on US federal land collecting it without a permit is illegal. Most suspected dinosaur bones turn out to be concretions, and the internal honeycomb texture is what tells you which you have.
Still not sure? Point a camera at it
A filter narrows fossils down to a shortlist. Orvik reads the photo itself and names the species, with the look-alikes ranked underneath so you can check the call yourself.