The modern mineral classification system, developed by the American geologist and mineralogist James Dwight Dana in the 1850s, categorizes more than 5,400 mineral species based on their dominant chemical compositions and crystalline structures. Professor Robert Hazen from the Carnegie Institution’s Geophysical Laboratory and George Mason University suggests an additional classification system, which could amplify existing knowledge of how minerals evolve over time without superseding the existing designations. In his new paper, published in the journal American Mineralogist, he argues for categories that reflect a deeper, more-modern understanding of planetary scale transformation over time.
This image shows tri-color crystals of elbaite, a mineral species belonging to the tourmaline group, on quartz. Image credit: Reno Chris.
“A system grouping minerals and non-crystalline natural solids — which are not currently classified by the existing system — into what I call ‘natural kind clusters’ would better reflect the inherent messiness of planetary evolution,” Professor Hazen said.
“For maximum efficacy, scientific classification systems must not just organize and define, but also reflect current theory, and allow it to expand and guide us to new conclusions.
Professor Hazen pioneered the concept of mineral evolution, linking an explosion in mineral diversity to the rise of life on Earth and the resulting oxygen-rich atmosphere.
He then added another layer to his vision by introducing mineral ecology, which analyzes the spatial distribution of Earth’s minerals to predict which ones remain undiscovered and to assert our planet’s mineralogical uniqueness.
A system of categorization that reflects not just a mineral’s chemistry and crystalline structure, but also the physical, chemical, or biological processes by which it formed, would be capable of recognizing that nanodiamonds from space are fundamentally different to diamonds formed in Earth’s depths.
The existing classification system groups some minerals with disparate formation histories together in one category, while splitting others with similar origin stories into separate mineral species.
Another example: currently 32 different mineral species of the tourmaline group are delineated by the distribution of the major elements of which they are comprised.
So, a single shard of tourmaline with slight variations in chemistry often contains multiple species of the mineral, even if they all formed in the same geologic event.
A natural kind classification system would rectify that problem, and allow for the inclusion of non-crystalline materials, such as volcanic glass, amber, and coal, which currently aren’t counted as minerals, but can offer knowledge about our evolving planet.
“Earth’s mineralogy tells vivid stories, revealing how eons of geologic activity and the rise of life facilitated novel combinations of elements,” Professor Hazen said.
“But to glean every nuance of this mineralogical text, we must embrace a new language for describing the creation of minerals that reflects the passage of time.”
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Robert M. Hazen. 2019. An evolutionary system of mineralogy: Proposal for a classification of planetary materials based on natural kind clustering. American Mineralogist 104 (6): 810-816; doi: 10.2138/am-2019-6709CCBYNCND
