sedimentary

Stromatolite

Laminated biogenic sedimentary structure (Cyanobacteria)

Hardness: 3-5 (varies by mineral Replacement); Color: alternating bands of gray, white, tan, and black; Luster: matte to dull; Structure: wavy, laminated layers; Cleavage: none; Specific Gravity: 2.6-2.8

Hardness: 3-5 (varies by mineral Replacement)
Color: alternating bands of gray, white, tan, and black
Luster: matte to dull

Identified June 15, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, primarily blue-green algae (cyanobacteria). These specimens date back as far as 3.5 billion years, representing some of the oldest evidence of life on Earth.

Uses & applications

Used in ornamental stone carving, lapidary work (cabochons), interior decoration, and as highly prized educational and museum display specimens due to their status as 'living fossils'.

Geological facts

Stromatolites provided the first oxygen on Earth through photosynthesis. While most famous as ancient fossils, living stromatolites can still be found today in Shark Bay, Australia.

Field identification & locations

Identify in the field by the distinct 'pancake' or cauliflower-like wavy laminations. Commonly found in Precambrian dolomites and limestones in places like the Gunflint Chert of Ontario, the Mary Ellen Mine in Minnesota, or the Atlas Mountains of Morocco.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite

sedimentary