Caption: The
mineral hazenite, named after Robert Hazen, which is only found
in one locality,
Mono Lake, California. Like hazenite, 22 percent of known minerals
are found in just
one locality. The image is courtesy of Courtesy of Hexiong Yang.
(August 26, 2015) New
research from a team led by Carnegie’s Robert Hazen predicts that Earth has
more than 1,500 undiscovered minerals and that the exact mineral diversity of
our planet is unique and could not be duplicated anywhere in the cosmos.
Minerals form from novel combinations of elements. These
combinations can be facilitated by both geological activity, including
volcanoes, plate tectonics, and water-rock interactions, and biological
activity, such as chemical reactions with oxygen and organic material.
Nearly a decade ago, Hazen developed the idea that the
diversity explosion of planet’s minerals from the dozen present at the birth of
our Solar System to the nearly 5,000 types existing today arose primarily from
the rise of life. More than two-thirds of known minerals can be linked directly
or indirectly to biological activity, according to Hazen. Much of this is due
to the rise of bacterial photosynthesis, which dramatically increased the
atmospheric oxygen concentration about 2.4 billion years ago.
In a suite of four related, recently published papers, Hazen
and his team—Ed Grew, Bob Downs, Joshua Golden, Grethe Hystad, and Alex
Pires—took the mineral evolution concept one step further. They used both
statistical models of ecosystem research and extensive analysis of
mineralogical databases to explore questions of probability involving mineral
distribution.
Caption Left: A
rhodochrosite specimen from Butte, Montana, courtesy of Robert Downs.
Caption Right: The
mineral rosasite, courtesy of Robert Downs.
They discovered that the probability that a mineral
“species” (defined by its unique combination of chemical composition and
crystal structure) exists at only one locality is about 22 percent, whereas the
probability that it is found at 10 or fewer locations is about 65 percent. Most
mineral species are quite rare, in fact, found in 5 or fewer localities.
“Minerals follow the same kind of frequency of distribution
as words in a book,” Hazen explained. “For example, the most-used words in a
book are extremely common such as ‘and,’ ‘the,’ and ‘a.’ Rare words define the
diversity of a book’s vocabulary. The same is true for minerals on Earth. Rare
minerals define our planet’s mineralogical diversity.”
Further statistical analysis of mineral distribution and
diversity suggested thousands of plausible rare minerals either still await
discovery or occurred at some point in Earth’s history, only to be subsequently
lost by burial, erosion, or subduction back into the mantle. The team predicted
that 1,563 minerals exist on Earth today, but have yet to be discovered and
described.