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Glossary Afforestation Planting forest on lands that were originally grasslands or shrublands. Avoided emissions Greenhouse gas emissions reductions resulting from the avoidance or reduction of an emitting activity (e.g., prevent- ing deforestation). Biochar A solid carbon product of biomass thermochemical conversion. Brucite Magnesium hydroxide mineral, Mg(OH)2, commonly formed together with serpentine during hydration of ultramafic rocks. Calciner A kiln where calcium carbonate is heated with natural gas to produce solid calcium oxide in a direct air capture liquid solvent system. Capillary or residual Immobilization of CO2 as a result of interaction with pore gas trapping space in a geologic storage reservoir. Carbon dioxide removal Intentional efforts to remove carbon dioxide from the atmosphere. Such efforts complement carbon capture and sequestration methods that primarily focus on reducing CO2 emissions from point sources such as fossil fuel power plants. Carbonates Minerals such as magnesite (MgCO3), calcite (CaCO3) and dolomite (MgCa(CO3)2). Formation of carbonate minerals by reaction of CO2 with Mg- and Ca-bearing silicates is com- monly called carbonation and carbon mineralization. Causticizer A reactor where calcium carbonate is precipitated in a liquid solvent direct air capture system. CO2e A unit of measure of the amount of CO2 that would have an equivalent global warming impact as a greenhouse gas of interest. 403
N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N Combustion The most oxidizer-enriched of the thermochemical conver- sion paths, where sufficient oxidizer such as air or oxygen is provided to ensure complete oxidation of biomass for the production of power and/or heat. Crust Relatively low density, SiO2-rich, uppermost layer of the solid Earth; oceanic crust is mafic and about 7 km thick; continental crust is intermediate to felsic, with more Si, Al, Na, K than oceanic crust, and a variable thickness averaging ~36 km. Exergy The capacity of energy to do physical work. Gasification A process where a gasifying agent such as steam, air, or CO2 is used to partially oxidize biomass and produce high yields of combustible gases. Hydrothermal A thermochemical process where biomass is converted to liquefaction produce predominantly liquids via heating in water, where the water acts as a reactant. Integrated assessment A quantitative tool for combining diverse fields (i.e., science, modeling economics, and policy) to assess an impact, in this case the impact of emissions or emissions reductions. Levelized cost of energy The net present value of energy production over the life- time of the generating source. Life cycle analysis or An assessment of all of the environmental impacts over the life cycle assessment lifetime of a product, from raw material to consumption. Listvenite Rock composed of carbonate minerals + quartz + Fe-oxides + Cr-rich oxides or silicates, produced by complete carbon- ation of peridotite, in which all Mg and Ca combine with CO2 to form carbonate minerals, most Fe forms oxides, and all SiO2 forms quartz. Mafic Rock containing ~45-53 wt% SiO2 and/or composed of >10 wt% Ca-rich plagioclase (>50% An), typically with olivine, pyroxenes, and amphiboles, and no quartz. Mafic lavas are basalts. Mafic plutonic rocks are gabbros (sensu lato). Some mafic intrusions host significant ore deposits (Ni, Cr, plati- num group elements). Gabbroic rocks with very abundant plagioclase are called anorthosites. 404
Glossary Mantle Relatively dense, ultramafic layer of the solid Earth, underly- ing the crust. The upper mantleâfrom the base of the crust to ~410 km depthâis composed of peridotite and contains abundant Mg-rich olivine. Negative emissions An approach that removes CO2 from the atmosphere to be technology sequestered. Olivine Mineral solid solution between endmembers forsterite (Mg- 2SiO4) and fayalite (Fe2SiO4). Olivine comprises more than 60% of Earthâs upper mantle, where it is > 88% forsterite. Ophiolite Block of oceanic crust and upper mantle, an oceanic plate, thrust onto a continental margin. Peridotite Ultramafic rock containing greater than 40% olivine (aka the gemstone âperidotâ). Peridotite comprises most of Earthâs upper mantle. Plagioclase A solid solution mineral, part of the feldspar group, with compositions ranging continuously from anorthite (An, CaAl2Si2O8) to albite (Ab, NaAlSi3O8), including bytownite (Byt, 70-90% An), labradorite (Lab, 50-70% An), andesine (30-50% An) and oligoclase (10-30% An). Plagioclase, par- ticularly labradorite, is a common constituent of crystalline basalt (mantle-derived lava) and its slowly cooled, plutonic equivalent gabbro, together with ~0-20% olivine and 0-40% pyroxenes. Progradation Sediment deposition in wetlands that results in lateral of growth of the seaward edge. Pyrolysis A highly oxidizer deficient or anoxic thermochemical process in which biomass is heated in the absence of air to produce liquids and gases, which may be upgraded to bio- fuels or directly combusted, and solid carbon-rich biochar, which may be combusted, gasified, or distributed in soil for storage and soil amendment Pyroxene Fe-Mg silicates including orthopyroxene, with Mg-end- member enstatite (En, Mg2Si2O6), and calcium-rich pyroxene with Mg-endmember diopside (Di, CaMgSi2O6). Mg-rich pyroxenes comprise 0-40% of mantle peridotites. Rocks with 405
N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N greater than 60% pyroxene with less than 10% feldspar are pyroxenites. Quartz SiO2 mineral. Reforestation Planting forest on lands that used to be forest, but were converted to another use. Serpentine Hydrous silicate minerals with Mg-endmembers Mg3Si2O5(OH)4. Formation of serpentine plus other minerals by hydration of ultramafic rocks is often called serpentini- zation. Rocks composed mainly of serpentine are called serpentinites. Polytypes of serpentine include chrysotile, lizardite, and antigorite. Chrysotile and lizardite are common products of low-temperature hydration of ultramafic rocks and of olivine and pyroxene in mafic rocks. Slaker A reactor where calcium oxide reacts with water to regener- ate calcium oxide for reuse in a causticizer as part of a liquid solvent direct air capture system. Solid sorbent The capture surface for direct air capture systems utilizing adsoption and desorption to a CO2-sorbent material. Solubility trapping Secondary trapping mechanism for geologic storage result- ing from dissolution of CO2 into an aquifer. Spreading ridge Narrow zone of extension and formation of new, igneous oceanic crust from basaltic partial melts of the upper mantle rising between two diverging tectonic plates. Subduction zone Thrust fault at zone of convergence between two tectonic plates where one plate is thrust beneath the other; typically, old oceanic crust is thrust into the mantle. Supercritical CO2 CO2 gas compressed to a fluid above its critical temperature and pressure. Transgression Migration of a tidal wetland into adjacent uplands as sea (of wetlands) levels rise. Ultramafic Rock containing < 45 wt% SiO2 and > 18 wt% MgO, and/ or composed of > 90 wt% âmafic minerals,â which are olivine, pyroxenes, amphiboles, and serpentines. Ultramafic 406
Glossary rocks including peridotite comprise most of Earthâs upper mantle to a depth of about 410 km below the surface, and also form igneous rocks that host significant ore deposits, including explosively emplaced kimberlites (diamonds), igneous intrusions including peridotites and pyroxenites (Ni, Cr, platinum group elements), and ultramafic lavas known as komatiites (Ni). Wollastonite Ca-silicate mineral CaSiO3 most commonly found where granitic intrusions reacted with limestones. 407