A new way of categorizing minerals

Not all diamonds have a common history. Some diamonds originated in space, while some diamonds originated in the Earth’s mantle. Five thousand years ago, a large meteorite that hit a carbon-rich sediment on Earth produced a striking diamond.

All diamonds have a different composition and genesis, but all are categorized as “diamonds” by an authoritative guide to minerals.

For many physical scientists, this inconsistency is not a problem. But there are some unanswered questions for planetary scientists, geobiologists, paleontologists, and others who seek to understand the historical context of minerals.

In collaboration with CU Boulder philosophy professor Carol Cleland, Carnegie’s Robert Hazen and Shaunna Morrison have addressed this shortcoming with a new “evolutionary” system of mineral classification – which includes historical data and reflects changes in mineral diversity and distribution over more than 4 billion years.

Hazen said, “We have gathered from very different fields of philosophy and planetary science to see if there is a rigorous way to introduce the dimension of time into discussions of the solid materials that make up the Earth.”

“The IMA mineral classification system dates back to the 19th century when geologist James Dwight Dana outlined a way to categorize minerals based on a unique combination of idealized compositions of major elements and geometrically idealized crystal structure.”

Morrison said, “For example, IMA defines quartz as pure silica, but the existence of this idealized version is completely fictional. Each specimen of quartz contains defects – traces of the formation process that make it unique. “

“This approach to the categorization system means that minerals with distinctly different historical origins are grouped together – as in the case of diamonds – while other minerals that share a common history of causes are separated.”

Cleland said, “Differences in the history of diamond or quartz crystal formation are critical because the conditions under which the sample was formed and the modifications it underwent are far more informative than the fact that the crystal qualifies as a diamond or quartz.”

A new system is needed to categorize minerals that include historical “natural species.”

Hazen, Morrison, and Cleland proposed a solution to the bootstrap approach based on historically discovered, information-rich chemical, physical, and biological properties of solid materials. This strategy allows scientists to build a historical system of mineral species, while remaining agnostic in relation to their basic theoretical principles.

Hazen said, “Minerals are the most durable, information-rich objects we can study to understand the origin and evolution of our planet. Our new evolutionary approach to mineral classification complements existing protocols and offers the opportunity to rigorously document Earth’s history. “

Journal reference:
  1. Carol E. Cleland et al., “Historical Natural Species and Mineralogy: Systematizing Contingencies in the Context of Need”, PNAS (2020). DOI: 10.1073 / pnas.2015370118