You found a heavy, stone-hard piece of wood with the grain still showing, and you want to know what it is and whether it is the real thing. This identifier reads the photo for growth rings, ray cells, bark, and the rod-and-dot pattern of palm wood, then names the replacement mineral (silica, agate, jasper, or opal) and the look-alike to rule out before you add it to the collection.
Reviewed by RockHoundR Field Team · Field identification & geology editors · Last verified
Quick answer
Genuine petrified wood preserves visible grain, growth rings, or the rod-and-dot pattern of palm wood. Upload a clear photo of a cut or broken face and the identifier returns three ranked matches naming the replacement mineral (silicified, agatized, jasperized, or opalized), the Mohs hardness, and the plain jasper or agate look-alike to rule out.
Petrified wood is fossilized wood: the original cellulose and lignin have dissolved away and been replaced, cell by cell, with silica or opal that hardened in place. Because the mineral takes the exact shape of the wood it replaced, growth rings, ray cells, knots, bark, and even insect borings survive in stone. That is what separates petrified wood from an ordinary pretty rock. If a specimen shows no trace of wood grain or cell structure, it is almost certainly plain jasper or agate, not petrified wood, no matter how wood-like the color looks.
The replacement mineral decides the name and the hardness. Most petrified wood is silicified, replaced by microcrystalline quartz (chalcedony), which gives it a waxy-to-glassy luster and a Mohs hardness of about 6.5 to 7, hard enough to scratch glass. When the chalcedony is translucent and banded it is called agatized wood; when it is opaque and richly colored by iron oxides (red, yellow, brown) it is jasperized wood. A smaller share is opalized, replaced by hydrated silica (opal), which is softer (Mohs 5.5 to 6.5), often more translucent, and sometimes shows a waxy sheen. Rarer specimens are replaced by calcite or pyrite. Reading the luster and translucency from a photo is the fastest way to narrow which replacement you are looking at.
Locality and botany add the final layer. The American West holds the world's richest petrified wood, from the Triassic conifer logs of the Petrified Forest in Arizona to the limb casts of Eden Valley, Wyoming, and the agatized beds of central Oregon. Petrified palm wood, the state stone of Texas and the state fossil of Louisiana, is unmistakable once you know the cue: rows of dark dots or rods (the sclerenchyma bundles of a palm trunk) with no concentric growth rings, because palms are monocots and do not grow rings the way conifers and hardwoods do. The identifier weights these patterns and classic localities when you tell it where the piece came from, and it never invents a locality you did not provide.
Reference pieces for the replacement types and the two most common look-alikes. Each card shows the single feature that places a specimen, or rules it out.
The general case: silica-replaced wood with growth rings, grain, or ray cells preserved. Waxy-to-glassy luster, Mohs ~7, scratches glass. If there is no cell structure at all, suspect plain jasper instead.
Photo: Mauro Cateb · wikimedia
Translucent, banded chalcedony replacement. Hold it to light and the bands glow while the wood grain still reads through them. The most collectible form.
Photo: Michael Gäbler · wikimedia
Opal (hydrated silica) replacement. Softer at Mohs 5.5 to 6.5, often more translucent with a waxy-to-resinous sheen. A steel knife may scratch it where chalcedony wood will not.
Photo: Wikimedia Commons contributor · wikimedia
Rows of dark rods or dots (sclerenchyma bundles) running through the piece, with NO concentric growth rings. Diagnostic of palm, a monocot. State stone of Texas.
Photo: Wikipedia · serper
The most common look-alike. Opaque silica with no cell structure, grain, or rings. Wood-brown jasper fools people constantly. No preserved botany means it is not petrified wood.
Photo: Wikipedia contributors · wikipedia
Banded chalcedony with no wood structure. Concentric or parallel bands that follow a nodule shape, not wood grain. Agatized wood differs by preserving the cellular pattern of the original log.
Photo: Wikipedia contributors · wikipedia
The replacement types and their two closest look-alikes side by side. Luster and hardness narrow the replacement; the presence of preserved grain settles wood versus not-wood.
| Specimen | Hardness (Mohs) | Luster | Habit | Field tell |
|---|---|---|---|---|
| Petrified Wood | 6.5-7 | vitreous to waxy | pseudomorphous after wood structure | Growth rings, grain, or ray cells preserved in silica. Mohs ~7. |
| Agatized Wood | 6.5-7 | vitreous | pseudomorph | Translucent banded chalcedony with the wood structure picked out. |
| Opalized Wood | 5.5-6.5 | vitreous | pseudomorph | Softer opal replacement (Mohs 5.5 to 6.5), more translucent, waxy sheen. |
| Petrified Palm Wood | 6.5-7 | vitreous to waxy | massive | Rows of dark rods or dots, no growth rings (a monocot). |
| Jasper | 6.5-7 | waxy | massive | Opaque silica, no grain or cell structure. Not petrified wood. |
| Agate | 6.5-7 | waxy | banded, botryoidal, nodular, massive | Banded chalcedony following a nodule, not wood grain. |
Silicified (chalcedony) wood
The default. Quartz-family replacement, waxy-to-glassy, Mohs ~7. Grain and rings usually clear.
Agatized wood
Translucent, banded chalcedony replacement. The most prized, with the wood structure picked out in agate.
Jasperized wood
Opaque, iron-stained red, yellow, or brown silica. Solid color, grain shows on a polished face.
Opalized wood
Replaced by hydrated silica (opal). Softer (Mohs 5.5 to 6.5), often more translucent, sometimes a waxy sheen.
Petrified palm wood
Monocot. Rows of dark rods or dots (sclerenchyma) and no growth rings. Texas and Louisiana classic.
Limb casts
Branch-shaped pieces filled with chalcedony or agate. Eden Valley, Wyoming is the type locality.
The mineral that replaced the wood sets the luster, the hardness, and the name. Read luster and translucency first.
Petrified wood is defined by the botanical structure that survived. The more of these you can see, the more confident the call.
A cut or broken surface shows growth rings, grain, or palm dots best. Natural light, fill the frame. JPG, PNG, or WebP up to 6MB.
Arizona, Oregon, Wyoming, Texas. Locality and botany weight the replacement type and the variety without inventing details.
Each match: the replacement mineral, the preserved structure to look for, Mohs hardness, and the look-alike to rule out.
Photos read grain, color, and luster well. The exact replacement chemistry and the tree species often need a cut face, a hand lens, or lab work, so the tool is honest about where it stops.
The RockHoundR app works offline, saves every find to your map, and overlays them onto 250,000+ rockhounding spots with geology and land-access data.
Look for preserved wood structure: growth rings on a cross-cut end, parallel grain and ray cells along the trunk, bark, knots, or the rod-and-dot pattern of palm wood. Genuine petrified wood keeps the exact cellular shape of the original log. If a piece shows none of that, only solid or banded color, it is almost certainly jasper or agate rather than petrified wood, however wood-like the color seems.
All three are silica replacements, separated by the form of silica. Agatized wood is translucent banded chalcedony and glows when backlit. Jasperized wood is opaque chalcedony colored red, yellow, or brown by iron oxides. Opalized wood is replaced by hydrated silica (opal), which is softer (Mohs 5.5 to 6.5), often more translucent, and shows a waxy or resinous sheen. Reading luster and translucency from the photo is the fastest way to tell them apart.
Petrified palm wood shows rows of dark dots or rods running through it with no concentric growth rings. Those rods are the sclerenchyma bundles that stiffen a palm trunk. Palms are monocots, so they never form the tree rings that conifers and hardwoods do. That rod-and-dot pattern with no rings is diagnostic. It is the state stone of Texas and the state fossil of Louisiana.
Silicified wood (the common chalcedony-replaced kind) sits at about Mohs 6.5 to 7, so it scratches glass and a steel knife will not scratch it. Opalized wood is softer, around Mohs 5.5 to 6.5, and a hard steel point may mark it. A piece that a fingernail or copper penny scratches is not silica-replaced and is more likely calcite-replaced wood or not petrified wood at all.
The American West is the richest source. Arizona's Petrified Forest holds Triassic conifer logs, central and eastern Oregon produce agatized and limb-cast wood, Eden Valley in Wyoming is famous for limb casts, and Washington has its own state gem petrified wood. Petrified palm wood comes from Texas and Louisiana. Always check collecting rules first, since national parks prohibit removal and other federal land has limits.
It depends on the land. Collecting is banned in national parks, including Petrified Forest National Park. On most BLM land, casual collection of petrified wood for personal use is allowed up to a daily and annual weight limit, with no sale and no use of power equipment. State and private rules vary, so confirm the land status before you keep a piece.
Yes. Upload a photo and get ranked identifications in your browser at no cost, three free IDs per day per device, with no signup or install. The RockHoundR app removes the daily limit, saves every find to a personal map, works offline at remote beds, and overlays results onto 250,000+ rockhounding spots with geology and land-access data.
Property data and reference imagery used on this page are cross-checked against the following sources.
Federal reference on silica replacement of wood, from Petrified Forest National Park.
Geologic background on the Triassic Chinle Formation and fossil-wood preservation.
Reference for replacement mineralogy, hardness, and localities used in the comparison table.
