Mineral of the Month

MINERAL OF THE MONTH

January 2012 - Mary Ellen Jasper

The mineral of the month for this update is Mary Ellen Jasper. Unless you live in Minnesota, you may not be familiar with this interesting form of microcrystalline quartz. This rock formed more than two billion years ago in the area that is now the Mesabi Iron Range in Northern, Minnesota. At that time one of the early life forms evolved in the ancient seas. These blue-green single-celled cyanobacteria contained chlorophyll and were able to harvest the energy of the sun to photosynthesize and produce their own food. Energy from sunlight was used to split carbon dioxide into carbon and oxygen. The carbon was absorbed, becoming part of the growing organism, and the oxygen was released into the atmosphere. Prior to the evolution of cyanobacteria, there was almost no oxygen in the atmosphere. Once these organisms developed, they proliferated and helped to trigger drastic changes in the earth's atmosphere, climate, and environment.

Some of the cyanobacteria lived in colonies that produced macro-scale structures called stromatolites. A drawing depicting what a stromatolite shoreline may have looked like during the latter part of the Archean period is shown below. Evidence of fossil stromatolite formations have been found throughout the world so these mushroom-shaped mounds dominated the shores of all the newly developing landmasses, including the area where the Mary Ellen Jasper developed.

The earliest stromatolite of confirmed origin dates to 2,724 million years ago. A recent discovery, however, provides strong evidence that microbial stromatolites extending as far back as 3,450 million years ago. These organisms were extremely resilient and adaptable, allowing them to be a major constituent of the fossil record for the first 3,500 million years of life on earth, with their abundance peaking about 1,250 million years ago.

Until the mid-1950s, scientists thought that stromatolites were long since extinct. That all changed in 1956 when living stromatolites were found in the Hamlin Pool located on the south end of Sharks Bay in Western Australia. Since then, live stromatolites have also been found in several sites in the Bahamas. Pictures of both are included below.

Stromatolites are stony structures built up by algae and cyanobacteria. The microbes live in gooey mats on the top surface of the structures. These mats trap fine sediments carried across them by tidal currents. As the mats fill in with sediments and become opaque, the microbes move upwards seeking sunlight. Stromatolites differ from normal fossils because they are formed by the activities of micro-organisms. They result from a combination of trapping, binding and precipitation of sediment.

One of the biggest impacts that stromatolites had on the earth was the release of free oxygen, which was a byproduct of their photosynthesis. When stromatolites first evolved, the earth's atmosphere had less than one percent oxygen. After the stromatolites evolved, significant amounts of oxygen did not accumulate in the atmosphere right away because of the vast quantities of oxidizable materials in the earth's crust as well as the dissolved eager-to-combine iron in the oceans. For more than a hundred million years, these materials absorbed any free oxygen that was produced. Mary Ellen Jasper developed not only from the remains of the stromatolites, but also from the oxidization of iron that was present in the area that is now northern Minnesota.

A few more pictures of Mary Ellen Jasper are included below. The first two pictures are of a thin polished slab. The first is displayed with front lighting and the second with back lighting.

Coincidently, I just polished a piece of Mary Ellen Jasper for a customer a couple of days ago. Here is a picture of that specimen.

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MINERAL OF THE MONTH

January 2012 - Mary Ellen Jasper

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