35-2 Quantifying the growth rate of primary dolomite in the presence of dissolved silica using crystal truncation rod method

Session: Minerals in Motion: Tracking Mineral Reactions Using In Situ and Synchrotron Techniques, A Celebration of the Career of Peter Heaney (Posters)

Presenting Author:

Authors:

Abstract:

Sedimentary dolomite (CaMg(CO₃)₂) constitutes some of the most important oil and gas reservoirs in the United States and around the world. Because of its natural abundance and economic importance, dolomite has been extensively studied in the past century. However, its formation mechanism remains enigmatic. The stark contrast in dolomite prevalence, marked by its great abundance in Proterozoic and Lower Paleozoic and its scarcity in Cenozoic, suggests a dramatic shift in the geochemical environments that inhibited dolomite formation. The inability to synthesize dolomite in modern seawater at room temperature further complicated our understanding of the sedimentary dolomite formation mechanism. Classical low-temperature synthesis experiments have been unsuccessful because the high hydration affinity of Mg²⁺ ions inhibits crystal growth. Recent studies, however, have shown that dissolved sulfide, polysaccharides, and microbial exopolymeric substances (EPS) can facilitate dolomite formation by lowering dehydration energy of Mg²⁺-water complexes at mineral surfaces. Yet, the increasing biological activity in Earth history is accompanied by decreasing abundance of sedimentary dolomite implying that sedimentary dolomite formation may be primarily controlled by an abiotic process. Recent laboratory work shows that dissolved silica at concentrations higher than 1 mM can promote disordered dolomite precipitation in normal seawater-like solutions. Here, we report the first direct measurement of dolomite growth rates on bulk crystal using synchrotron-based crystal truncation rod (CTR) analysis, visualizing molecular-scale interfacial processes during the heterogeneous synthesis of primary dolomite at Earth’s surface conditions. Our results demonstrate that up to 4 angstroms of dolomite can grow epitaxially in the presence of dissolved silica within an hour. While the precipitated surface layers follow the crystallographic orientation of the bulk crystals, they do not have cation ordering and result in a larger unit cell parameter than the bulk crystal. This mismatch in unit cell size would exert strain between the bulk crystal and the surface layers and result in nucleating on new sites rather than single continuous growth. This direct quantification of dolomite growth rates sheds new light on the abundance of sedimentary dolomite in the rock record. Moreover, this work would provide insights into past and future carbon sequestration and the global carbon cycle.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7285

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.