Microscopic view of nanosized hematite particles forming on basaltic glass.

Iron's Tiny Secret: How Nanoscale Hematite Impacts Our Oceans

Kai Mendoza in Climate & Environment August 2025 • 4 min read.

"Unlocking the Mysteries of Iron Oxide in Basaltic Glass and Its Role in Global Biogeochemical Cycles"

The alteration of oceanic basalts stands as a cornerstone process, deeply intertwined with Earth's climate dynamics. Basalt alteration acts as a substantial sink for atmospheric carbon dioxide (CO2), helping to regulate our planet's temperature over geological timescales. This process also influences the composition of seawater, highlighting its pervasive impact on our marine environment.

Basalt rock contains iron and in fresh basalts, the dominant iron species is ferrous iron (Fe(II)). When oceanic basalts interact with oxygen-rich environments, such as the seafloor, Fe(II) oxidizes into Fe(III). This oxidation leads to the precipitation of iron-containing compounds, including hydroxides and oxides, on the basalt surface. The low solubility of Fe(III) at neutral pH further drives this deposition, creating secondary minerals.

Among these secondary minerals, iron(III) (hydr)oxides are commonly observed in basaltic rocks and glasses, resulting from both abiotic and biotic oxidation processes. These compounds have a large surface area and positive charge, making them pivotal in iron and phosphorus cycling within marine ecosystems. Understanding these processes and the specific types of Fe(III) (hydr)oxides formed is critical for assessing their bioavailability and impact on marine life.

Why Does the Size and Structure of Fe(III) Matter for Ocean Health?

Microscopic view of nanosized hematite particles forming on basaltic glass.

Iron(III) (hydr)oxides exhibit a variety of forms, including ferrihydrite, goethite, hematite, akaganeite, and lepidocrocite. Each species has distinct physical properties and bioavailabilities. The rate at which Fe-reducing bacteria can process these compounds varies significantly, making precise identification essential for understanding their role in marine environments.

Particle size and structural order also influence how these minerals behave. Smaller, more disordered particles exhibit increased solubility, enhancing their bioavailability. This is critical because the transformation of iron from less soluble to more soluble forms can stimulate microbial activity and nutrient cycling in otherwise nutrient-limited environments.

Increased Surface Area: Nanosized particles have a dramatically larger surface area compared to their bulk counterparts, leading to enhanced reactivity.
Enhanced Solubility: Smaller particles tend to dissolve more readily, making iron more accessible to marine organisms.
Unique Electronic Properties: The electronic structure of nanoparticles can differ from that of bulk materials, affecting their interactions with other compounds and biological systems.

Researchers used multiple techniques including micro X-ray absorption near edge structure (µXANES), micro extended X-ray absorption fine structure (μEXAFS), transmission electron microscopy (TEM), and TEM- electron energy loss spectroscopy (EELS) to characterize secondary Fe(III) (hydroxides in altered basalt glass. These techniques provided direct information on the species, crystallinity, and particle size of Fe(III) (hydr)oxides.

Why This Matters: Connecting Microscopic Discoveries to Global Impacts

This research highlights the importance of understanding nanoscale processes in the ocean. The discovery of nanosized hematite in altered basaltic glass provides new insights into iron cycling and its potential influence on marine ecosystems. By connecting microscopic observations with global biogeochemical cycles, scientists can better predict how these processes will respond to future environmental changes.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.chemgeo.2018.10.005, Alternate LINK

Title: Μxafs And Tem Studies Of Fe(Iii) Oxides Precipitated On Submarine Basaltic Glass From South Pacific Gyre

Subject: Geochemistry and Petrology

Journal: Chemical Geology

Publisher: Elsevier BV

Authors: S. Mitsunobu, Y. Suzuki, K. Watanabe, K. Yang, J.W. Kim

Published: 2018-11-01

Everything You Need To Know

Why is the alteration of oceanic basalts important for Earth's climate?

The alteration of oceanic basalts is a crucial process because it acts as a significant sink for atmospheric carbon dioxide (CO2). This helps in regulating Earth's temperature over long geological timescales. In fresh basalts, ferrous iron (Fe(II)) is dominant, but when basalts interact with oxygen-rich environments, Fe(II) oxidizes into ferric iron (Fe(III)), leading to the precipitation of iron-containing compounds. This process also impacts the composition of seawater, underscoring its broad influence on the marine environment. Other related processes not mentioned include the release of other elements during basalt alteration, which can further influence ocean chemistry and biological productivity.

What are some common types of iron(III) (hydr)oxides found in basaltic rocks, and why is identifying them important?

Common types of iron(III) (hydr)oxides found in basaltic rocks include ferrihydrite, goethite, hematite, akaganeite, and lepidocrocite. Identifying these specific compounds is vital because each has distinct physical properties and bioavailabilities. The rate at which Fe-reducing bacteria can process these compounds varies significantly, affecting iron and phosphorus cycling within marine ecosystems. Without precise identification, it's hard to accurately assess their bioavailability and impact on marine life.

How do the size and structure of iron(III) (hydr)oxides affect their behavior in marine environments?

The size and structural order of iron(III) (hydr)oxides significantly influence their behavior in marine environments. Smaller, more disordered particles exhibit increased solubility, enhancing their bioavailability. This transformation of iron from less soluble to more soluble forms can stimulate microbial activity and nutrient cycling in otherwise nutrient-limited environments. Nanosized particles also have a larger surface area, leading to enhanced reactivity and unique electronic properties that can affect their interactions with other compounds and biological systems. Factors such as aggregation and surface coatings, which aren't explicitly mentioned, could further influence their behavior.

What methods were used to characterize secondary iron(III) (hydroxides) in altered basalt glass, and what kind of information did these methods provide?

Researchers employed techniques such as micro X-ray absorption near edge structure (µXANES), micro extended X-ray absorption fine structure (μEXAFS), transmission electron microscopy (TEM), and TEM-electron energy loss spectroscopy (EELS) to characterize secondary iron(III) (hydroxides) in altered basalt glass. These methods provided direct information on the species, crystallinity, and particle size of the iron(III) (hydr)oxides. These methods are essential because they provide complementary data, enabling a more complete understanding of the composition and structure of these materials at the nanoscale. Other methods such as atomic force microscopy (AFM) could be used to measure surface properties and reactivity.

How does the discovery of nanosized hematite in altered basaltic glass contribute to our understanding of marine ecosystems and global biogeochemical cycles?

The discovery of nanosized hematite in altered basaltic glass offers new insights into iron cycling and its potential influence on marine ecosystems. Nanosized particles have increased surface area, enhanced solubility and unique electronic properties. By connecting microscopic observations with global biogeochemical cycles, scientists can better predict how these processes will respond to future environmental changes. This research underscores the importance of understanding nanoscale processes in the ocean and their potential to impact global systems. The long-term implications for carbon sequestration and nutrient availability in the oceans are significant areas for future investigation.