diagram {CHNOSZ}R Documentation

Chemical Activity Diagrams


Plot equilibrium chemical activity (1-D speciation) or equal-activity (2-D predominance) diagrams as a function of chemical activities of basis speecies, temperature and/or pressure.


  diagram(eout, what = "loga.equil", alpha = FALSE, normalize = FALSE,
    as.residue = FALSE, balance=NULL, groups=as.list(1:length(eout$values)),
    xrange=NULL, mar=NULL, yline=par("mgp")[1]+0.3, side=1:4,
    ylog=TRUE, xlim=NULL, ylim=NULL, xlab=NULL, ylab=NULL,
    cex=par("cex"), cex.names=1, cex.axis=par("cex"),
    lty=NULL, lwd=par("lwd"), dotted=NULL,
    col=par("col"), col.names=par("col"), fill=NULL,
    fill.NA="slategray1", limit.water=TRUE,
    names=NULL, main=NULL, legend.x=NA, format.names=TRUE, adj=0.5, dy=0,
    add=FALSE, plot.it=TRUE, tplot=TRUE, ...)
  strip(affinity, ispecies = NULL, col = NULL, ns = NULL, 
    xticks = NULL, ymin = -0.2, xpad = 1, cex.names = 0.7)



list, object returned by equilibrate or affinity


character, what property to calculate and plot


logical or character (balance), for speciation diagrams, plot degree of formation instead of activities?


logical, divide chemical affinities by balance coefficients (rescale to whole formulas)?


logical, divide chemical affinities by balance coefficients (no rescaling)?


character, balancing constraint; see equilibrate


list of numeric, groups of species to consider as a single effective species


numeric, range of x-values between which predominance field boundaries are plotted


numeric, margins of plot frame


numeric, margin line on which to plot the y-axis name


numeric, which sides of plot to draw axes


numeric, limits of x-axis


numeric, limits of y-axis


character, label to use for x-axis


character, label to use for y-axis


logical, use a logarithmic y-axis (on 1D degree diagrams)?


numeric, character expansion (scaling relative to current)


numeric, character expansion factor to be used for names of species on plots


numeric, character expansion factor for names of axes


numeric, line types to be used in plots


numeric, line width


numeric, how often to skip plotting points on predominance field boundaries (to gain the effect of dotted or dashed boundary lines)


character, color of activity lines (1D diagram) or predominance field boundaries (2D diagram), or colors of bars in a strip diagram (strip)


character, colors for labels of species


character, colors used to fill predominance fields


character, color for grid points with NA values


logical, set NA values beyond water stability limits?


character, names of species for activity lines or predominance fields


character, a main title for the plot; NULL means to plot no title


character, description of legend placement passed to legend


logical, apply formatting to chemical formulas?


numeric, adjustment for line labels


numeric, y offset for line labels


logical, add to current plot?


logical, make a plot?


logical, set up plot with thermo.plot.new?


list, object returned by affinity


numeric, which species to consider (default of NULL is to consider all species)


numeric, numbers of species, used to make inset plots for strip diagrams


numeric, location of supplemental tick marks on x-axis


numeric, lower limit of y-axis


numeric, amount to extend x-axis on each side


matrix, value of the predominant list element from diagram


additional arguments passed to plot or barplot


diagram takes as its primary input the results from equilibrate and displays diagrams representing the equilibrium chemical activities of the species. 0-D diagrams, at a single point, are shown as barplots. 1-D diagrams, for a single variable on the x-axis, are plotted as lines. 2-D diagrams, for two variables, are plotted as predominance fields. The allowed variables are any that affinity accepts: temperature, pressure, or the chemical activities of the basis species

If groups is supplied, the activities of the species identified in each numeric element of this list are multiplied by the balance coefficients of the species, then summed together. The names of the list are used to label the lines or fields for the summed activities of the resulting groups.

For all diagrams, the names of the species and their colors in col.names can be changed, as can cex, cex.names, and cex.axis to adjust the overall character expansion factors (see par) and those of the species names and axis labels. The x- and y-axis labels are automatically generated unless they are supplied in xlab and ylab. A new plot is started unless add is TRUE. If plot.it is FALSE, no plot will be generated but all the intermediate computations will be performed and the results returned.

find.tp finds the locations in a matrix of integers that are surrounded by the greatest number of different values. The function counts the unique values in a 3x3 grid around each point and returns a matrix of indices (similar to which(..., arr.ind = TRUE)) for the maximum count (ties result in more than one pair of indices). It can be used with the output from diagram for calculations in 2 dimensions to approximately locate the triple points on the diagram.


For speciation diagrams (1-D), an invisible list of the chemical activities of the species, or their degrees of formation (if alpha is TRUE), at each point. For predominance diagrams (2-D), an invisible list with elements species, the dataframe describing the species, out, which species predominates at each grid point, and A, a list of the calculated values of the chemical affinity (per balanced quantity) (log10 dimensionless) at each point.

1-D diagrams

For 1-D diagrams, the default setting for the y-axis is a logarithmic scale (unless alpha is TRUE) with limits corresponding to the range of logarithms of activities (or 0,1 if alpha is TRUE); these actions can be overridden by ylog and ylim. If legend.x is NA (the default), the lines are labeled with the names of the species near the maximum value. Otherwise, a legend is placed at the location identified by legend.x, or omitted if legend.x is NULL.

If alpha is TRUE, the fractional degrees of formation (ratios of activities to total activity) are plotted. Or, setting alpha to balance allows the activities to be multiplied by the number of the balancing component; this is useful for making “percent carbon” diagrams where the species differ in carbon number. The line type and line width can be controlled with lty and lwd, respectively.

2-D diagrams

On 2-D diagrams, the fields represent the species with the highest equilibrium activity. fill determines the color of the predominance fields, col that of the boundary lines. By default, heat.colors are used to fill the predominance fields in diagrams on the screen plot device. fill can be any color specification, or the word rainbow, heat, terrain, topo, or cm, indicating a palette from grDevices. fill.NA gives the color for empty fields, i.e. points for which NA values are present, possibly by using equilibrate at extreme conditions (see test-diagram.Rd). fill.NA is also used to specify the color outside the water stability limits on Eh-pH or pe-pH diagrams, when limit.water is TRUE. Note that the default for fill.NA is automatically changed to transparent when add is TRUE.

The default line-drawing algorithm uses contour to draw smooth-looking diagonal and curved lines, at the expense of not coinciding exactly with the rectangular grid (which is still used for drawing colors). lty, col, and lwd can be specified, but limiting the lines via xrange is not currently supported. To go back to the old behavior for drawing lines, set dotted to 0. The old behavior does not follow lty; instead, the style of the boundary lines on 2-D diagrams can be altered by supplying one or more non-zero integers in dotted, which indicates the fraction of line segments to omit; a value of 1 or NULL for dotted has the effect of not drawing the boundary lines.

normalize and as.residue apply only to the 2-D diagrams, and only when eout is the output from affinity. With normalize, the activity boundaries are calculated as between the residues of the species (the species divided by the balance coefficients), then the activities are rescaled to the whole species formulas. With as.residue, the activity boundaries are calculated as between the residues of the species, and no rescaling is performed.

Affinity Diagrams

The function behaves differently when the output from affinity is being used instead of the equilibrium activities from equilibrate. If what is missing, and the number of dimensions is 0 or 1, a property of a reaction, such as the equilibrium constant (logK), is plotted.

If what is missing, and the number of dimensions is 2, then highest potential (equilibrium predominance) fields are plotted. This algorithm is based on comparing the relative magnitudes of the affinities of the formation reactions, also referred to as the maximum affinity method. In this case, the balancing coefficients are determined usingi the balance argument.

If what is the name of a basis species, it indicates to plot the equilibrium activity of a selected basis species in all of the formation reactions. A contour plot is made in the case of 2-D diagrams of the equilibrium activity of a basis species (see the CO2-acetic acid example in buffer, and only the first species of interest is used in the calculation; a warning is produced if there is more than one.

Activity Coefficients

The wording in this page and names of variables in functions refer exclusively to activities of aqueous species. However, if activity coefficients are calculated (using the IS argument in affinity), then these variables are effectively transformed to molalities (see tests/testthat/ test-logmolality.R). So that the labels on diagrams are adjusted accordingly, diagram sets the use.molality argument of axis.label to TRUE if IS was supplied as an argument to affinity. The labeling as molality takes effect even if IS is set to 0; this way, by including (or not) the IS = 0 argument to affinity, the user decides whether to label aqueous species variables as molality (or activity) for calculations at zero ionic strength (where molality = activity).

Strip Diagrams

A different incarnation of 1-D speciation diagrams is provided by strip. This function generates any number of strip diagrams in a single plot. The diagrams are made up of colors bars whose heights represent the relative abundances of species; the color bars are arranged in order of abundance and the total height of the stack of colors bars is constant. If ispecies is a list, the number of strip diagrams is equal to the number of elements of the list, and the elements of this list are numeric vectors that identify the species to consider for each diagram. The strips are labeled with the names of ispecies. If col is NULL, the colors of the bars are generated using rainbow. Supplemental ticks can be added to the x-axis at the locations specified in xtick; they are larger than the standard ticks and have colors corresponding to those of the color bars. ymin can be decreased in order to add more space at the bottom of the plot, and xpad can be changed in order to increase or decrease the size of the x-axis relative to the width of the strips. An inset dot-and-line plot is created below each strip if ns is given. This argument has the same format as ispecies, and can be used e.g. to display the relative numbers of species for comparison with the stability calculations.


Aksu, S. and Doyle, F. M. (2001) Electrochemistry of copper in aqueous glycine solutions. J. Electrochem. Soc. 148, B51–B57. https://doi.org/10.1149/1.1344532

Helgeson, H. C. (1970) A chemical and thermodynamic model of ore deposition in hydrothermal systems. Mineral. Soc. Amer. Spec. Pap. 3, 155–186. http://www.worldcat.org/oclc/583263

Helgeson, H. C., Delany, J. M., Nesbitt, H. W. and Bird, D. K. (1978) Summary and critique of the thermodynamic properties of rock-forming minerals. Am. J. Sci. 278-A, 1–229. http://www.worldcat.org/oclc/13594862

LaRowe, D. E. and Helgeson, H. C. (2007) Quantifying the energetics of metabolic reactions in diverse biogeochemical systems: electron flow and ATP synthesis. Geobiology 5, 153–168. https://doi.org/10.1111/j.1472-4669.2007.00099.x

Majzlan, J., Navrotsky, A., McClesky, R. B. and Alpers, C. N. (2006) Thermodynamic properties and crystal structure refinement of ferricopiapite, coquimbite, rhomboclase, and Fe2(SO4)3(H2O)5. Eur. J. Mineral. 18, 175–186. https://doi.org/10.1127/0935-1221/2006/0018-0175

See Also

Other examples are present in the help for protein and buffer, and even more can be found in demos. See the vignette Hot-spring proteins in CHNOSZ for an example of the strip charts.


## calculate the equilibrium logarithm of activity of a 
## basis species in different reactions
species(c("ethanol", "lactic acid", "deoxyribose", "ribose"))
a <- affinity(T=c(0, 150))
diagram(a, what="O2", legend.x="topleft", col=rev(rainbow(4)), lwd=2)
title(main="Equilibrium logfO2 for 1e-3 mol/kg of CO2 and ... ")

### 1-D diagrams: logarithms of activities

## Degrees of formation of ionized forms of glycine
## After Fig. 1 of Aksu and Doyle, 2001 
species(ispecies <- info(c("glycinium", "glycine", "glycinate")))
a <- affinity(pH=c(0, 14))
e <- equilibrate(a)
diagram(e, alpha=TRUE, lwd=1)
title(main=paste("Degrees of formation of aqueous glycine species\n",
  "after Aksu and Doyle, 2001"))

## Degrees of formation of ATP species as a function of 
## temperature, after LaRowe and Helgeson, 2007, Fig. 10b
# to make a similar diagram, activity of Mg+2 here is set to
# 10^-4, which is different from LH07, who used 10^-3 total molality
basis(c("CO2", "NH3", "H2O", "H3PO4", "O2", "H+", "Mg+2"),
  c(999, 999, 999, 999, 999, -5, -4))
species(c("HATP-3", "H2ATP-2", "MgATP-2", "MgHATP-"))
a <- affinity(T=c(0, 120, 25))
e <- equilibrate(a)
diagram(e, alpha=TRUE)  
title(main=paste("Degrees of formation of ATP species,\n",
  "pH=5, log(aMg+2)=-3. After LaRowe and Helgeson, 2007"),

### 2-D diagrams: predominance diagrams
### these use the maximum affinity method

## Fe-S-O at 200 deg C, after Helgeson, 1970
basis(c("Fe", "O2", "S2"))
species(c("iron", "ferrous-oxide", "magnetite",
  "hematite", "pyrite", "pyrrhotite"))
# the calculations include the phase transitions of
# pyrrhotite; no additional step is needed
a <- affinity(S2=c(-50, 0), O2=c(-90, -10), T=200)
diagram(a, fill="heat")
title(main=paste("Fe-S-O, 200 degrees C, 1 bar",
  "After Helgeson, 1970", sep="\n"))

## pe-pH diagram for hydrated iron sulfides,
## goethite and pyrite, after Majzlan et al., 2006
basis(c("Fe+2", "SO4-2", "H2O", "H+", "e-"), 
  c(0, log10(3), log10(0.75), 999, 999))
species(c("rhomboclase", "ferricopiapite", "hydronium jarosite",
  "goethite", "melanterite", "pyrite"))
a <- affinity(pH=c(-1, 4, 256), pe=c(-5, 23, 256))
d <- diagram(a, main="Fe-S-O-H, after Majzlan et al., 2006")
# the first four species show up in order near pe=15
stopifnot(all.equal(unique(d$predominant[, 183]), 1:4))
water.lines(d, lwd=2)
text(3, 22, describe.basis(thermo$basis[2:3,], digits=2, oneline=TRUE))
text(3, 21, describe.property(c("T", "P"), c(25, 1), oneline=TRUE))

## Temperature-Pressure: kayanite-sillimanite-andalusite
# cf. Fig. 49 of Helgeson et al., 1978
# this is a system of one component (Al2SiO5), however:
# - number of basis species must be the same as of elements
# - avoid using H2O or other aqueous species because of
#     T/P limits of the water() calculations;
# - because it triggers calculations for phase transitions,
#    (takes more time), don't use quartz unless it's needed
basis(c("corundum", "chalcedony", "oxygen"))
species(c("kyanite", "sillimanite", "andalusite"))
# database has transition temperatures of kyanite and andalusite
# at 1 bar only, so we permit calculation at higher temperatures
a <- affinity(T=c(200, 900, 99), P=c(0, 9000, 101), exceed.Ttr=TRUE)
d <- diagram(a, fill=NULL)
bexpr <- sapply(c("Al2O3", "SiO2", "H2O"), expr.species, simplify=FALSE)
btext <- substitute(Al2O3 - SiO2 - H2O, unlist(bexpr))
mtitle(c(as.expression(btext), "after Helgeson et al., 1978"))
# find the approximate position of the triple point
tp <- find.tp(d$predominant)
Ttp <- a$vals[[1]][tp[1, 2]]
Ptp <- rev(a$vals[[2]])[tp[1, 1]]
points(Ttp, Ptp, pch=10, cex=5)
# some testing of the overall geometry
stopifnot(species()$name[d$predominant[1, 1]]=="andalusite")
stopifnot(species()$name[d$predominant[1, 101]]=="kyanite")
stopifnot(species()$name[d$predominant[99, 101]]=="sillimanite")

[Package CHNOSZ version 1.1.3 Index]