Mineral Ecology: Chance and Necessity in the Mineral Diversity of Terrestrial Planets

Abstract

Four factors contribute to the roles played by chance and necessity in determining mineral distribution and diversity at or near the surfaces of terrestrial planets: (1) crystal chemical characteristics; (2) mineral stability ranges; (3) the probability of occurrence for rare minerals; and (4) stellar and planetary stoichiometries in extrasolar systems.The most abundant elements generally have the largest numbers of mineral species, as modeled by relationships for Earth's upper continental crust (E) and the Moon (M), respectively: LogðN E Þ ¼ 0:22 LogðC E Þ þ 1:70 ðR 2 ¼ 0:34Þð4861 minerals; 72 elementsÞ LogðN M Þ ¼ 0:19 LogðC M Þ þ 0:23 ðR 2 ¼ 0mineral species await discovery or could have occurred at some point in Earth's history, only to be subsequently lost by burial, erosion, or subduction-i.e., much of Earth's mineral diversity associated with rare species results from stochastic processes.Measurements of stellar stoichiometry reveal that stars can differ significantly from the Sun in relative abundances of rock-forming elements, which implies that bulk compositions of some extrasolar Earth-like planets likely differ significantly from those of Earth, particularly if the fractionation processes in evolving stellar nebulas and planetary differentiation are factored in. Comparison of Earth's upper continental crust and the Moon shows that differences in element ratios are reflected in ratios of mineral species containing these elements.In summary, although deterministic factors control the distribution of the most common rock-forming minerals in Earth's upper continental crust and on the Moon, stochastic processes play a significant role in the diversity of less common minerals. Were Earth's history to be replayed, and thousands of mineral species discovered and characterized anew, it is probable that many of those minerals would differ from species known today.

Mineral Species Frequency Distribution Conforms to a Large Number of Rare Events Model: Prediction of Earth’s Missing Minerals

“…By contrast, 22 % of mineral species have been found at only one locality and 12 % are found at only two localities, while more than half of all mineral species are found at five or fewer localities. Hazen et al (2015) proposed that the frequency distribution of mineral species with rare occurrence indicates that many more mineral species are yet to be discovered, have occurred in the past but are lacking on Earth today, or never formed owing to chance events.…”

“…Mineral diversity is defined as the number of different mineral species, each of which has a unique combination of crystal structure and chemical composition as approved by the International Mineralogical Association (http://rruff.info/ima). Deterministic factors in mineral diversity are illustrated by the positive correlation between the abundances of crustal elements and the numbers of mineral species containing those elements (Hazen et al 2015). The most common and volumetrically significant minerals, which form from the most abundant crustal chemical elements (including oxygen, silicon, iron, magnesium, aluminum, and calcium), are known as the rock-forming minerals.…”

“…The frequency distribution of mineral species in Earth's near-surface environment, as well as on other terrestrial planets and moons, arises from both deterministic factors and chance events (Hazen et al 2015). Mineral diversity is defined as the number of different mineral species, each of which has a unique combination of crystal structure and chemical composition as approved by the International Mineralogical Association (http://rruff.info/ima).…”

Earth’s “missing” minerals

“…Previous authors have identified a correlation between the crustal abundance of an element and the number of mineral species incorporating that element ( Fig. 1; Yaroshevsky and Bulakh 1994;Higgins and Smith 2010;Christy 2015;Hazen et al 2015).…”

“…Earth's mineralogical diversity and distribution arise from both deterministic processes and frozen accidents (Grew and Hazen 2014;Hazen et al 2015). For example, chance and necessity both play a role in the distribution of mineral species among the 72 essential mineral-forming chemical elements.…”