Petrified algae, often found as stromatolites, are fossilized microbial mats that have been replaced by silica. They are prized by collectors for their distinctive layered or cauliflower-like internal banding and earthy, multi-toned color patterns.

Hardness

6.5-7

Mohs

Luster

Waxy

Streak

White

Transparency

Opaque

fossilcommon

Petrified Algae

Also: Stromatolite

Hardness: 6.5-7
Luster: Waxy
Streak: White
Transparency: Opaque

Is this petrified algae?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch petrified algae with a known reference. Petrified Algae sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Petrified Algae leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Petrified Algae typically shows a waxy luster.
4
Match the color range
Compare against the expected color range: tan, brown, gray, red, cream.
5
Look at form & habit
Typical habit: botryoidal, layered, massive, columnar.

Often confused with

Petrified Algae vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside petrified algae

Minerals reported to co-occur with petrified algae. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: SiO₂
Mohs hardness: 6.5-7
Density: 2.6-2.7 g/cm³
Colors: Tan Brown Gray Red Cream
Streak: White
Luster: Waxy
Transparency: Opaque
Crystal habit: Botryoidal, Layered, Massive, Columnar
Cleavage: None
Rarity: Common
Uses: Lapidary, Collector, Decorative
Host rock: Sedimentary
Typical price: $10-100 per specimen

Where rockhounds find petrified algae

1 mapped spots

Classic worldwide localities

Wyoming, USA
Bolivia
Australia
Morocco
Canada

Field-hunting tip

Look in sedimentary country, the host setting where petrified algae typically forms. If you start seeing quartz, chalcedony, calcite in float, you are in the right ground. Field specimens usually show a botryoidal, layered, massive, columnar habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Nevada. Start trip planning there.

Browse 1 U.S. spots for petrified algae →

Common questions

How do you identify petrified algae?+

Mohs hardness is 6.5-7. It typically shows a waxy luster. The streak is white. Common colors include tan, brown, gray, red.

Where is petrified algae found?+

Notable localities include Wyoming, USA; Bolivia; Australia; Morocco; Canada.

Can I find petrified algae in the United States?+

RockHoundR maps 1 petrified algae rockhounding spots across 1 U.S. states. The top states are Nevada.

How much is petrified algae worth?+

Typical asking prices fall in the range of $10-100 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like petrified algae?+

Petrified Algae is most often confused with Agate, Jasper, Flint Nodules. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with petrified algae?+

Petrified Algae commonly co-occurs with Quartz, Chalcedony, Calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does petrified algae form in?+

Petrified Algae typically forms in sedimentary. Working float back to the host body is the standard way to chase a fresh occurrence.

What is petrified algae used for?+

Petrified Algae is used in lapidary, collector, decorative.

Find petrified algae on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.