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Alexander V. Sobolev is a geologist whose research in geochemistry uses basalt compositions to investigate mantle melting and the recycling of oceanic crust. In a 2005 study of Hawaiian basalts, he and collaborators argued that the high nickel and silicon contents of many inferred parental magmas were inconsistent with melting a deep source containing olivine in equilibrium with pyroxene.^[ref]

Their proposed mechanism was a reaction between melts derived from recycled oceanic crust and mantle peridotite. Consumption of olivine would produce an olivine-free pyroxenite source with different chemical controls on subsequent melts. This is an example of using mineral–melt relations to test a mantle source model: the erupted basalt carries indirect evidence about deep rocks that cannot be sampled in place. The proposed pyroxenite contribution concerns these Hawaiian magmas, rather than implying that the whole mantle lacks olivine.^[ref]

A family of commonly hydrous silicate minerals with double-chain structures, important in amphibolite and many igneous rocks.

Biologically controlled or influenced production of mineral material. Its evolutionary distribution affects mechanical function and the probability that a body part enters the fossil record.

Chemical weathering alters or dissolves exposed rock and minerals through reactions with water, gases and dissolved substances. The reaction rate depends on mineral composition, temperature, reactive surface area and the supply and removal of fluid. Fracturing can accelerate weathering by exposing fresh surfaces.

In silicate weathering, reactions involving carbon dioxide connect rock alteration with the long-term carbon cycle. The eventual climate effect also depends on transport, carbonate burial and recycling. A classic feedback model links warmer conditions with increased weathering and carbon-dioxide removal; its operation requires suitable rocks and water supply.^[ref]

A group of sheet-silicate minerals; an idealized Mg-rich composition used in weathering models is $\mathrm{M}{\mathrm{g}}_5\mathrm{A}{\mathrm{l}}_2\mathrm{S}{\mathrm{i}}_3{\mathrm{O}}_{10}(\mathrm{OH}{)}_8$. Its alteration to gibbsite or kaolinite depends on dissolved silica and the magnesium-to-proton thermodynamic activity ratio.

Fine-grained hydrous silicate minerals with structures and surface properties important to adsorption and water-rock interaction.

Suppose two dissolution reactions to a reference mineral $C$ have been normalized to the same amount of a conserved reference component. After division by the same positive energy factor, let their Gibbs energies of reaction be $y-{\ell }_1(x)$ and $y-{\ell }_2(x)$. Their relative thermodynamic potentials can then be written as displayed. The stable mineral has the smallest potential.

It follows that $C$ is stable below $y=\min ({\ell }_1,{\ell }_2)$, mineral 1 is stable where ${\ell }_1<{\ell }_2$ and $y>{\ell }_1$, and mineral 2 is stable where ${\ell }_2<{\ell }_1$ and $y>{\ell }_2$. The two nonreference minerals coexist stably where ${\ell }_1={\ell }_2<y$. Their equality below that height is a metastable continuation. This comparison proves the stable lower envelope and selects which portions of the pairwise mass-action lines belong on the mineral activity diagram.

For a mineral reaction producing one mole of water, let $H^{\circ },S^{\circ }$ refer to the $P^{\circ }$ standard state and let the solids’ volume change $\Delta V_s$ be constant. If $A_s$ is the product/reactant solid-activity ratio, the Gibbs energy of reaction isFor temperature-independent specified activities and fugacity, equilibrium givesThe gas pressure work is already represented by the fugacity term; adding a second constant water-volume term double counts it. For an ideal gas, $f=P$; a given fugacity coefficient gives $f={\varphi }_{f}P$. If these quantities depend on temperature, the equilibrium equation must instead be solved implicitly. Pressure units in the solid volume correction must match those used for $\Delta V_s$.

Ferdinand Reich investigated zinc minerals using chemical separation and spectrum analysis. With Hieronymus Theodor Richter, he identified indium in 1863 after finding a spectral feature inconsistent with the expected thallium. The episode illustrates how a distinctive spectral line can guide the isolation of a new chemical element.^[ref]

A scientist associated with the identification of indium.

Verified external portrait reference: Portrait or portrait collection identifying the sitter.

A small trapped fluid pocket in a mineral, preserving evidence of fluid composition and trapping conditions, subject to later modification.

Fractional crystallization changes a residual geological melt by removing crystals as they form. Different minerals accept different elements into their structures, so the removed solid generally has a different composition from the remaining liquid. Successive removal can progressively enrich components that enter the early crystals weakly.

Settling, flotation or flow through a crystal-rich region can separate the phases. The resulting cumulate rock and residual melt need not have the same bulk chemistry. This is a cooling and separation process; partial melting instead starts by producing liquid from an incompletely melted rock.

Coauthor of research on electron exchange between bacterial cytochromes and iron minerals. The study connected exposed membrane proteins with the transfer of electrons to materials outside the cell.^[ref]

An aluminium hydroxide mineral with composition $\mathrm{Al}(\mathrm{OH}{)}_3$. In a simplified mineral activity diagram, it is favored over kaolinite at sufficiently low dissolved silica thermodynamic activity.

A common descriptive name for low-grade metamorphosed mafic volcanic rock, often containing greenish minerals. A greenstone belt can contain these rocks together with other volcanic and sedimentary rocks; the belt name does not imply uniform composition or density.

Hieronymus Theodor Richter and Ferdinand Reich identified indium through spectrum analysis of material obtained from a zinc mineral. The unusual indigo-coloured spectral line distinguished the new chemical element from thallium, which Reich had initially sought. Their joint 1863 paper reported the new substance.^[ref]

A chemist associated with the identification of indium.

Verified external portrait reference: Portrait or portrait collection identifying the sitter.

Imaging in many narrow, usually adjacent wavelength bands. Relative to broad-band multispectral imaging, it can resolve narrower mineral absorption features in spectral reflectance, helping distinguish surface lithologies, at the cost of data volume and often reduced signal per band.

The observable physical and compositional character of rock, including its constituent minerals, texture and grain size. Different lithologies can have distinct spectral reflectance, density and magnetic susceptibility, making geological mapping possible through several independent measurements.

A magnesium- or iron-rich silicate mineral, such as olivine, pyroxene or many amphiboles.

A rock relatively rich in magnesium- and iron-bearing silicate minerals. Basalt and gabbro are common examples; their magnetic susceptibility depends particularly on magnetic-mineral abundance.

Mars is a terrestrial planet with a thin, mainly carbon dioxide atmosphere. Its reddish surface contains oxidized iron minerals. Ancient channels, sedimentary deposits and water-altered minerals preserve evidence of past liquid water; they do not imply that the same surface conditions persist today.^[ref]

The scientific opportunity is to compare a planet's present climate with its geological record. Orbital imaging maps landforms, while measurements of local rocks constrain their composition and formation. Interpreting those observations together helps distinguish erosion by flowing water from other mechanisms. Mars also preserves crustal magnetization despite lacking a present global magnetic field, providing a separate record of its interior evolution.^[ref]