Introduction
The tabulated estimates present the mass concentration of each chemical element in Earth’s crust, expressed in milligrams per kilogram (mg/kg), which is numerically identical to parts per million (ppm) by mass. Because 10,000 ppm equals 1% by mass, for example, 100 ppm corresponds to 0.01% of the crust. Reporting abundances in mg/kg (ppm) allows direct comparison of elements that occur as major, minor, trace, or ultra‑trace constituents.
These values represent bulk, averaged concentrations for the crustal reservoir rather than measurements at specific sites; they are synthesized from numerous analyses across rock types and regions to characterize typical crustal proportions. Users must therefore recognize substantial spatial and stratigraphic heterogeneity: concentrations differ systematically between continental and oceanic crust, among upper, middle and lower crustal levels, and with lithology (e.g., felsic versus mafic compositions). Consequently the table is most appropriate for regional-to-global mass‑budgeting and geochemical modeling, not for predicting local concentrations.
Read more Government Exam Guru
The ppm framework supports a range of quantitative applications, including mass‑balance calculations, models of crustal differentiation and magmatic/metamorphic behavior, assessments of geochemical cycles, and estimates of global element inventories relevant to resources and environmental baselines. At the same time, abundance estimates carry methodological uncertainty arising from sample selection and weighting, analytical technique (e.g., XRF vs. ICP‑MS), how lithologic diversity is treated, and assumptions about which crustal reservoirs are included. Reported ppm values should therefore be used with an appreciation of their representativeness and error margins when informing exploration, resource evaluation, or environmental comparisons.
Reservoirs
In geochemical and geographic practice, a reservoir is any large, bounded body treated as a single unit for quantifying elemental abundance and distribution. Commonly employed reservoirs for Earth studies include the ocean, atmosphere, mantle and crust; each is characterized as a discrete domain whose bulk composition, element budgets and internal variability are quantified and compared with others. The continental crust, in particular, functions as one principal reservoir whose overall composition and heterogeneity are central to studies of surface element inventories.
Free Thousands of Mock Test for Any Exam
Distinctive relative abundances of elements among reservoirs arise because different chemical and physical mechanisms operate during their formation and subsequent evolution. Chemical fractionation, mineral crystallization, solubility contrasts and reaction pathways control how elements partition between phases and thus concentrate or deplete particular reservoirs. Superimposed on these chemical processes are mechanical redistributions—physical segregation, sedimentation, tectonic transport and particle sorting—that move material between domains and modify the proportion of elements retained within any given reservoir.
Methodologically, reservoirs are treated as coherent units for mass‑balance and budget calculations, but such treatments must explicitly recognize internal heterogeneity and the dynamic fluxes that connect reservoirs across space and time. Accurate interpretation of elemental abundance data therefore requires simultaneous consideration of which reservoir is being measured (ocean, atmosphere, mantle, crust) and the chemical and mechanical processes that produced and continue to reshape its composition.
Estimating elemental abundances in the Earth, and particularly in the continental crust, is intrinsically challenging because the crust is not a homogeneous reservoir. Vertical compositional contrasts between the upper and lower crust mean that a single bulk estimate conflates chemically distinct layers and can therefore misrepresent the true distribution of elements between those reservoirs.
Spatial heterogeneity compounds this problem: crustal composition varies markedly from place to place as a consequence of differences in lithology, tectonic history, magmatic and metamorphic activity, and surface processes. Localized sampling campaigns therefore risk producing results that are not representative of broader crustal domains unless their geographic and geological context is explicitly accounted for.
Post-formation processes have further modified the crust since planetary accretion. Loss of volatiles, repeated episodes of partial melting and recrystallization that fractionate elements, the transport of elements into the deep interior during differentiation and mantle–crust exchange, and ongoing erosion and sedimentary redistribution all alter present-day abundances relative to an original bulk composition. In particular, the removal or concentration of specific elements into the mantle or core complicates attempts to reconstruct original crustal chemistries.
Certain element groups are especially difficult to quantify accurately; rare-earth (lanthanide) elements are notable for larger uncertainties in crustal abundance estimates than many major or accessory elements. Given vertical and lateral heterogeneity together with the suite of post-formation modifications, reliable abundance determinations require stratified, regionally calibrated geological models and rigorous sampling and analytical strategies rather than simple extrapolation from limited or unstratified datasets.
Graphs of abundance versus atomic number
Plots of atom‑fraction abundance for chemical elements in the upper continental crust, displayed as a function of atomic number, reveal systematic regularities that combine astrophysical origin with planetary-scale redistribution. In typical graphical encodings siderophile elements are highlighted (commonly in yellow) to emphasize their distinct behavior relative to lithophile and chalcophile groups.
The broad shape of the abundance curve reflects two sets of controls. First, stellar nucleosynthesis establishes a baseline distribution of elemental production — including the pronounced alternation in abundance between even and odd atomic numbers known as the Oddo–Harkins effect, which derives from nuclear stability and favored production pathways in stars. Second, planetary differentiation and surface processes rework that baseline: metal–silicate segregation, sulfide formation, volatile loss and near‑surface geochemical sorting selectively enrich or deplete particular elements in the crust.
Read more Government Exam Guru
Siderophile elements exemplify the effects of planetary differentiation. By virtue of their affinity for metallic iron they were partitioned into Earth’s core during segregation, producing anomalously low atom fractions in the upper crust despite not being the most massive elements. This core‑sequestration contrasts with compositions of undifferentiated meteoritic material, which retain relatively high siderophile abundances and thus underscore the role of core formation in crustal depletion.
Certain elements show additional, element‑specific behavior. Selenium and tellurium were concentrated into sulfide phases and further partitioned into metal during core formation; they were also subject to preaccretional volatile losses in the solar nebula because they formed volatile hydrides (H2Se, H2Te), which promoted their removal from the reservoir that built the terrestrial crust.
In sum, the crustal atom‑fraction pattern plotted against atomic number is a composite signal: a primary nucleosynthetic imprint (including the Oddo–Harkins alternation) modified by planetary processes such as core segregation, sulfide partitioning and volatile preaccretional chemistry, which together produce the distinctive depletions and enrichments observed in crustal abundance graphs.
Free Thousands of Mock Test for Any Exam
Dataset description
The dataset summarizes the average composition of the continental crust by mass, reported primarily in parts per million (ppm) with percent-by-mass values where given. Each entry pairs atomic number, element identity and symbol, a Goldschmidt geochemical affinity (lithophile, siderophile, chalcophile, atmophile or trace), an abundance value, and annual extraction (tonnes per year) when available. Reported abundances for scarce elements can vary by several orders of magnitude at local scales.
Dominant constituents
Four elements—oxygen (O), silicon (Si), aluminium (Al) and iron (Fe)—account for the bulk of continental-crust mass. Oxygen and silicon together exceed 70 wt% (O ≈ 46.1%, Si ≈ 28.2%), with aluminium (~8.2%) and iron (~5.6%) making up most of the remainder. Reported annual extraction rates for these elements are very large (for example Fe and Al are extracted in the 10^6–10^9 t/yr range), reflecting both their abundance and industrial demand.
Major rock-forming and near-surface elements
Other common lithophile elements that form most rocks occur at percent-to-tenth-percent levels: calcium (~4.15%), sodium (~2.36%), magnesium (~2.33%) and potassium (~2.09%), with titanium at roughly 0.565%. Extraction rates vary widely by element and use (e.g., Na and K-bearing commodities show very large tonnages for industrial and agricultural applications).
Volatiles and biologically important elements
Several elements essential to life or volatile cycles occur at the hundred-ppm scale: hydrogen (~1,400 ppm), phosphorus (~1,050 ppm), manganese (~950 ppm), fluorine (~585 ppm), barium (~425 ppm), strontium (~370 ppm), sulfur (~350 ppm) and carbon (~200 ppm). Although occuring at low ppm compared with major rock-formers, some of these species have very large fluxes; most notably the reported carbon extraction is on the order of 10^9 t/yr, and nitrogen extraction is also substantial.
Intermediate-abundance suite (≈165–19 ppm)
A broad group of transition metals, halogens and rare-earth elements occupies the mid-range abundances (tens to low hundreds ppm). Examples include zirconium (~165 ppm), chlorine (~145 ppm), vanadium (~120 ppm), chromium (~102 ppm), rubidium (~90 ppm), nickel (~84 ppm), zinc (~70 ppm), various light rare-earths (Ce, La, Nd, etc.), cobalt and lithium. Annual extraction figures in this group range from negligible to millions of tonnes, underscoring that crustal abundance alone does not determine production volume.
Lower-abundance to rare elements (≈14–0.015 ppm)
Many trace metals, heavy rare-earths and semi-metals occur at single-digit to sub-ppm concentrations: lead (~14 ppm), boron (~10 ppm), thorium (~9.6 ppm), a suite of lanthanides and heavy REEs (several ppm to sub-ppm), uranium (~2.7 ppm), and numerous chalcophile and siderophile elements (e.g., arsenic, tin, molybdenum, tungsten). Reported extraction rates for these elements are heterogeneous; some are economically important with substantial annual production, while others have minimal or unlisted extraction.
Very-low-abundance, precious and noble-group elements (≤0.0085 ppm)
Platinum-group metals, gold and certain atmophile gases occur at sub-ppb to sub-ppm levels (for example Au ≈ 0.004 ppm, Pt ≈ 0.005 ppm). Despite their extreme scarcity in the crust, many of these elements are mined at measurable rates because of high economic value and concentrated ore deposits.
Extremely trace and radioactive species
A number of radionuclides and highly unstable species are present only at vanishingly small concentrations (orders of magnitude below ppm), e.g., protactinium, radium, actinium and trace entries for technetium, promethium, astatine, francium and transuranic elements. Quantitative abundance and extraction data are generally not provided for these species.
Geochemical synthesis
The continental crust is strongly enriched in lithophile elements (O, Si, Al, Ca, Na, K, Mg, etc.), which dominate its mass and define common rock compositions. Siderophile and chalcophile elements are present at much lower average concentrations but may be locally enriched in ore bodies. Atmophile elements occur at low ppm yet can participate in very large fluxes (notably C and N). Finally, annual extraction tonnages do not scale directly with crustal abundance: economic value, concentration into mines, technological demand and flux processes jointly determine production rates, producing large disparities between abundance and extraction for many elements.