It has taken fifteen years but now researchers have detailed every known mineral on Earth. As well as being a comprehensive inventory, the repository will allow other scientists to look into the history of the Earth. In addition, the data set will aid with the search for new minerals, either on Earth or other planets.
The impressive research exercise comes from Carnegie Institution for Science. To come up with the data set, the researchers used 57 different approaches. These involved combinations of crushing, boiling, baking and sometimes zapping the samples.
Each specimen in the collection is referred to as a ‘mineral kind’ and there are 10,556 different samples. This advances considerably the 6,000 minerals known about before the study began (as recognised by the International Mineralogical Association). The figure of 10,556 is reached by combinations of minerals species and means of origin.
The reason for the large leap in new minerals was that prior to the research, minerals were defined on the basis of their crystal structure and chemical composition.
Earth has far more minerals compared with the Moon, as well as what scientists believe to be on Mars and Mercury. The reason for this is due to the abundance of water on our planet (which probably accounts for the existence of 80 percent of the know minerals). Another factor is due to Earth’s oxygen rich atmosphere and the presence of lifeforms. Life is thought to have accounted for around 1,900 minerals.
The biological connection is important since 40 percent of Earth’s mineral species required the action of cells.
Another factor with mineral species is that, in many causes, different processes needed to combine in order to create the minerals. The maximum number of ‘recipes’ is 15 and nine minerals have been established as requiring 15 different processes. Such processes include biological activity, lightning or meteor strikes, changes caused by water-rock interactions, transformations at high pressures, and extreme temperatures.
Often time spans of hundreds of millions of years, at different stages of the Earth’s 4.5 billion year-old history, were required to create the minerals. However, it is reasoned that the vast majority of minerals formed within the first 250 million years of the Earth’s existence.
Some 296 known minerals appear to pre-date Earth itself. The majority of these will have come from meteorites. The oldest known minerals are zircon crystals, which are almost 4.4 billion years old.
Sometimes different combinations of processes create the same mineral. For instance, with pyrite (commonly called ‘Fool’s Gold’, composed of one part iron to two parts sulphide), this mineral forms at high temperature and low temperature, with and without water, and sometimes with the help of microbes. Pyrite is also derived from meteorites, volcanos, hydrothermal deposits, by pressure between layers of rock, near-surface rock weathering, microbially-precipitated deposits, plus several mining-associated processes like coal mine fires.
In addition, diamonds originate in at least nine ways, including condensation in the cooling atmospheres of old stars, during a meteorite impact, and under hot ultra-high-pressure deep within the Earth.
Another interesting finding is that just 41 elements are essential constituents of 42 percent of Earth’s minerals. These include arsenic, cadmium, gold, mercury, silver, titanium, tin, uranium, and tungsten.
The research appears in two papers, both published in the journal American Mineralogist. The first is titled “On the paragenetic modes of minerals: A mineral evolution perspective”. The second is called “Lumping and splitting: Toward a classification of mineral natural kinds.”
