Stromatolite

Mineralogy of Stromatolite

Rough Fossil Stromatolite, Lester Park, Saratoga Springs, New York, USA

Rock Type: Sedimentary Rock (Limestone) created by cyanobacteria
Major Minerals: Calcite

Color: Varies by type of rock, usually brown or gray with black markings, but can also be red or green with black markings
Gravity: Unknown
Hardness: 4-7
Luminescence: Unknown
Texture: Laminated layers
Transparency: Opaque

Location: Stromatolites were formed when the Earth’s continents were still fused together as a supercontinent. As a result, Stromatolites can be found all over the world. Some of the more notable locations include Australia, Bolivia, Brazil, Madagascar, Mexico, Mongolia, Namibia, Peru, South Africa, and the United States.

Rock Type: Stromatolite is not a mineral, but rather a very unique kind of sedimentary rock. An easy way to understand the difference is that rocks are like cookies and minerals are ingredients such as flour or sugar. Many different minerals are used to create a rock! Stromatolites typically form as Limestone, so their main mineral ingredient is usually Calcite. These Stromatolites are typically brown or grey, with black markings. Occasionally Stromatolites form as Sandstone, with the main mineral ingredients being Quartz or Feldspar. Feldspar-Sandstone Stromatilites appear vivid green with black markings, and are usually called Kambamba Jasper. Regardless of their color or mineral composition – what makes Stromatolites so unique is that these sedimentary rocks contain fossils of the earliest life forms on this planet!

Formation: Stromatolites are formed in shallow, salty water teeming with microorganisms, particularly cyanobacteria (blue-green algae). These tiny living creatures form massive colonies and sediments, such as sand and mud, get stuck to the sticky surface of this living mass of cyanobacteria. The sediments are gradually set down in layers and react to the trace minerals in the water. Over time, they form Limestone or Sandstone rocks, often shaped like a mushroom or a loaf. While underwater, the Stromatolite is “alive” – part cyanobacteria colony, part sedimentary material. If the water evaporates, or other conditions change, the cyanobacteria dies and the structure hardens further. At this point, it becomes a more typical sedimentary rock – but one containing microscopic fossils of the cyanobacteria. Stromatolites are some of the oldest rocks on the planet, with some examples dating back over 3.5 billion years! Stromatolites are still being formed today in a few rare locations. As a result, Stromatolite is often called a “living fossil.” (For more information, see the History Tab).

Mining: Little information is available about the mining of Stromatolites, except that they are almost certainly mined at their primary deposit. Most of the brown/black Stromatolites currently on the market are described as being “from Peru.” In reality, most would have been mined in the Andes Mountains of central Bolivia, near the city of Cochabamba, and then sold in Lima, Peru to dealers. These particular Stromatolites are estimated to be between 2.2-2.4 billion years old.

The Andes overlooking Cochabamba, Bolivia

Enhancements: All Stromatolites are completely natural, enhanced only by tumbling, cutting, and polishing.

Map courtesy of TravelBlog
Photos: Raw Stromatolite, Cochambamba