Viscosity Of Silicate Melts Research Articles

AlO1.5/SiO2 substitution effect on the viscosity of alkali silicate melts

The effect of alumina addition on the viscosity of silicate melts is strongly related to the type of non-framework cations; however, the origin of these interactions is not well understood. In this study, we measured the viscosity change in selected alkali disilicate (R2O·2SiO2, R: Na or Li) melts by varying the AlO1.5/SiO2 molar ratio (AlO1.5 = 0–16.8 mol%) within the 1373–1823 K temperature range. We observed that as the molar ratio increased, sodium silicate viscosity increased, whereas lithium silicate viscosity was not affected. Aluminum-27 nuclear magnetic resonance spectra of the quenched glasses indicated that the aluminum cations in both types of alkali silicate melts were mostly present as AlO4 tetrahedra. In contrast to sodium-containing systems, the shear strain on the AlO4 tetrahedron was greater for lithium aluminosilicate glass. Our findings indicated that the degree of shear strain on AlO4 plays an essential role in controlling the viscosity of aluminosilicate systems.

Reconstruction of smelting conditions during 16th‐ to 18th‐century copper ore processing in the Kielce region (Old Polish Industrial District) based on slags from Miedziana Góra, Poland

AbstractThis study presents the first reconstruction of the smelting conditions in 16th‐ to 18th‐century smelters from Miedziana Góra (Holy Cross Mountains, Poland). Based on geochemical (inductively coupled plasma mass spectrometry/emission spectrometry, X‐ray fluorescence) and mineralogical analysis (X‐ray diffractometry, scanning electron microscopy, electron probe micro‐analysis) of historical slags, their chemical/phase composition and the basic smelting parameters (temperature, melt viscosity, and oxygen fugacity) were determined. Due to the differences in chemical and phase composition, slags from different smelting stages have been distinguished: hypocrystalline slags (MG6) from speiss/matte production and glassy (MG1–MG5) from matte conversion. In glassy slags, pyroxenes, quartz/cristobalite grains, and aggregates composed of metallic Cu and PbO are dispersed in the glass. Hypocrystalline slags are composed of wollastonites, anorthites, and metallic Cu. The temperature range at which the slags were formed was from ~1100°C (solidus temperature) to 1150–1200°C (liquidus temperature). The silicate melt's viscosity was from log η = 1.19 to 4.42 Pa s (at 1100–1200°C). The higher viscosity of MG1–MG5 slags indicates that, unlike MG6 slags, they were not formed during gravity separation. Information about the phase composition made it possible to determine the oxygen fugacity in the range of log fO2 = −4 to −12 atm. High oxygen fugacity indicates the oxidizing nature of the smelting process.

Models for Viscosity of Geological Melts

Research Article| May 01, 2022 Models for Viscosity of Geological Melts James K. Russell; James K. Russell Earth, Ocean and Atmospheric Sciences The University of British Columbia Vancouver, V7W-2S1, British Columbia, Canada krussell@eoas.ubc.ca Search for other works by this author on: GSW Google Scholar Kai-Uwe Hess; Kai-Uwe Hess Department of Earth and Environmental Sciences Ludwig-Maximilians-University Munich Theresienstr. 41 / III 80333, Munich, Germany Search for other works by this author on: GSW Google Scholar Donald B. Dingwell Donald B. Dingwell Department of Earth and Environmental Sciences Ludwig-Maximilians-University Munich Theresienstr. 41 / III 80333, Munich, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information James K. Russell Earth, Ocean and Atmospheric Sciences The University of British Columbia Vancouver, V7W-2S1, British Columbia, Canada Kai-Uwe Hess Department of Earth and Environmental Sciences Ludwig-Maximilians-University Munich Theresienstr. 41 / III 80333, Munich, Germany Donald B. Dingwell Department of Earth and Environmental Sciences Ludwig-Maximilians-University Munich Theresienstr. 41 / III 80333, Munich, Germany krussell@eoas.ubc.ca Publisher: Mineralogical Society of America First Online: 01 May 2022 Copyright © 2022 by the Mineralogical Society of AmericaMineralogical Society of America Reviews in Mineralogy and Geochemistry (2022) 87 (1): 841–885. https://doi.org/10.2138/rmg.2022.87.18 Article history First Online: 01 May 2022 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation James K. Russell, Kai-Uwe Hess, Donald B. Dingwell; Models for Viscosity of Geological Melts. Reviews in Mineralogy and Geochemistry 2022;; 87 (1): 841–885. doi: https://doi.org/10.2138/rmg.2022.87.18 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Viscosity is the single most important physical property governing the formation, transport and eruption of naturally occurring silicate melts and magmas. Silicate melt viscosity is of fundamental interest to earth scientists, and in particular petrologists, volcanologists and geophysicists, because of the role it plays in governing melt production, magma ascent processes, styles of volcanic eruption, as well as, rates of physicochemical processes (e.g., degassing, crystallization). The viscosity of natural silicate magmas is a complex function of the temperature–pressure–composition dependence of the melt viscosity plus the non-linear effects due to the presence of included phases such as crystals and gas/fluid-filled bubbles... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Ann-Based Model to Predict the Viscosity of Silicate Melt at Ultrahigh Temperatures of >1600 Kelvin

Ann-Based Model to Predict the Viscosity of Silicate Melt at Ultrahigh Temperatures of >1600 Kelvin

Increasing the strength of pellets made of titanium-magnetite concentrates when using additives containing barium and strontium

In the process of pelletizing of titanium-magnetite ores concentrate, the high viscosity of the forming titaniferous melts makes the pellets sintering difficult resulting in their low strength. The reserves of the existing methods of solving the problem by addition of oxides of waste rock and therefore decreasing titanium concentration or by assortment of optimal heat mode of the technological process are exhausted. An ability to decrease the viscosity of titaniferous melt by application monoxides of iron, manganese, boron and alkali oxides of potassium, sodium and strontium for its dilution was considered. It was shown that the alkali additives were a powerful method to decrease the viscosity of silicate melts. The purpose of the study was to estimate an ability to in-crease the strength of iron ore pellets of titanium-magnetite concentrates by addition barium-strontium carbonate ores of Murunskoye deposit into the charge, which have and increased content of oxides of barium and strontium (up to 19% BaO and up to 5% of SrO). As a result of the experiment a mechanism of pellets strengthening at addition carbonate barium-strontium ores was established. The increase of the burnt pellets strength was reached up to 35–40%. It was shown, that the pellets strengthening was stipulated by modi- fication of slag melt structure with destruction of polymer chains and by decrease of melt viscosity. The increase of pellets strength will contribute to decreasing of fines yield during their transportation and to improving of gas-dynamic mode of shaft facilities – blast furnaces and metallization furnaces. The forecast effect due to application of additives in the pellets is estimated as follows: decrease of coke rate by 4.5–5.8 kg/t of hot metal and decrease of cast iron cost by 49.5–64.3 Rbl/t of cast iron.

Modeling the viscosity of silicate melts containing Fe oxide: Fe saturation condition

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing iron oxide. In the present study, the viscosity experimental data under the reduced atmosphere, which is Fe saturation condition were critically reviewed and three pairs of adjustable model parameters related to ‘FeO’ were optimized to best reproduce all experimental data in the FeO–SiO2–Al2O3–CaO–MgO–Na2O–MnO–Ti2O3–TiO2 system. The viscosities of a wide compositional and temperature range of binary, ternary and multicomponent melts were well reproduced by the present model within the scatter of experimental data.

Modeling the viscosity of silicate melts containing Fe oxide: FeO/Fe2O3 containing system

In the present study, the viscosity experimental data for the FetO-containing silicate melts under oxidation atmosphere, which Fe3+ and Fe2+ co-exist were critically evaluated and model parameters related to Fe2O3 were optimized to best reproduce all reliable experimental viscosity data. The charge compensation effect on the viscosity for the systems containing Fe2O3 was modeled with the Gibbs energies for LiFe, NaFe, KFe and CaFe2 “associate species” formation. The viscosities of a wide compositional and temperature range of binary, ternary and multicomponent melts containing Fe2O3–FeO–SiO2–Al2O3–CaO–MgO–Li2O–Na2O–K2O–MnO–Ti2O3–TiO2 were well reproduced by the present model within the scatter of experimental data.

Different Roles of Iron Species in the Network Structure and Viscosity of Silicate Melts

In iron-containing silicate melts such as gasification slags and geological slags, iron can play a different role in the melt properties because of its varying valence states. In this paper, the st...

Unravelling the effect of nano-heterogeneity on the viscosity of silicate melts: Implications for glass manufacturing and volcanic eruptions

Traditionally depicted as homogeneous materials, manmade and volcanic glasses are often subjected to nanostructuration during demixing and crystallization of their parental melt. While the controlled formation of nanocrystals has been exploited for decades in the industrial production of glass-ceramics to obtain materials with superior properties, nano-heterogeneities have been recently recognized in volcanic products erupted explosively. Here, a multi-pronged approach is adopted to highlight how the emergence of nano-heterogeneities exerts a previously unexplored influence on the viscosity of multicomponent silicate melts. Calorimetry and viscometry provide evidence of how the formation of TiO2- and FeO-bearing nanocrystals increases the effective viscosity of suspensions. Raman spectroscopy and transmission electron microscopy allow the correlation between the increase in viscosity and the degree of sample modification. This study has implications for glass and glass-ceramics manufacturing and for the development of better numerical models of volcanic eruptions, which are key for the operational assessment of volcanic risk.

A Preliminary Model for the Migration of Sulfide Droplets in a Magmatic Conduit and the Significance of Volatiles

Abstract A close relationship between Ni–Cu–(PGE) sulfide deposits and magmatic conduit systems has been widely accepted, but our present understanding still rests on empirical inductions that sulfide liquids are entrained during magma ascent and aggregated at hydrodynamic traps such as the opening of a conduit into a larger magma body. In this contribution, a preliminary quantitative model for the dynamics of mm-scale sulfide droplets in a vertical magmatic conduit is developed, examining such limiting parameters as the size, transport velocity and the magmas’ maximum carrying capacity for sulfide droplets. Addition of numerous dense sulfide droplets significantly reduces magma buoyancy and rapidly increases the bulk viscosity, and the resulting pressure gradient in the propagating conduit dyke restricts the maximum volume fraction of droplets that can be carried by ascending magma. For sulfide droplets alone, the maximum carrying capacity is low, but it will be improved dramatically by the addition of volatiles which reduces the density and viscosity of silicate melt. Potential volatile degassing during decompression further facilitates sulfide entrainment by reducing bulk magma density, and the formation of buoyant compound vapour-sulfide liquid bubble drops also greatly enhances the carrying capacity. The breakdown of compound drops by detachment of parts of the vapour bubble or sulfide droplet may occur at low pressure, which liberates sulfide liquids from rising compound drops, potentially to collect in traps in the conduit system. When sulfide-laden magma flows through a widening conduit, many droplets can be captured by the re-circulation flow just downstream of the expanding section, followed by sulfide liquid accumulation and enhanced chemical interaction via diffusive exchange with the recirculating magma, potentially resulting in an economic, high-tonnage ore body. We apply our models to the emplacement of sulfide-rich magmatic suspensions at Noril’sk and show that the disseminated mineralization in intrusions could have formed when magmas carrying re-suspended sulfide liquid entrained from pre-existing sulfide accumulations in the conduit system reached their limiting sulfide carrying capacity as dictated by buoyancy and were deflected into blind sills flanking the principal conduit for flood basalt volcanism.

A calibrated database of Raman spectra for natural silicate glasses: implications for modelling melt physical properties

AbstractThe physical properties of silicate melts are of critical importance for understanding magmatic and volcanic processes on Earth and other planets. Most physical properties of melts are, ultimately, a consequence of the structural organization of the melt. Robust and fully generalizable strategies for the prediction of properties of naturally occurring melts as functions of composition, temperature, and pressure remain a challenging goal. Given the structural origin of macroscopic properties, Raman spectroscopy of glasses, which provides information on melt and glass structure, may provide a useful technique to understanding and quantify variations in macroscopic melt properties. Here, with the aim of providing a generalizable model for predicting the viscosity of silicate melts, we present the results of a Raman spectroscopy campaign performed on 30 anhydrous multicomponent silicate glasses resulting from quenching of remelted and homogenized volcanic rocks and synthetic equivalents. The sample suite comprises one of the largest databases of multicomponent melts for which (a) chemical compositions and (b) physical properties (i.e., viscosity, fragility, heat capacity, and glass transition temperature) are known. Raman spectra have been collected using green light sources at wavelengths of 532 nm. Spectra were collected on the same sample suite in four independent laboratories involving instruments from different manufacturers and, thus, using different spectrometers, detectors, and analytical conditions. Our results are also compared and integrated with published data on some of the same samples derived from two others setups using green light sources with 514.5 and 532 nm wavelegths. For the same sample, the Raman spectra acquired using different setups show different intensities and intensity ratios. However, a strategy based on the ratio between the low‐ and high‐wavenumber peaks (R) was developed to standardize the data to normalized Raman ratios (Rn) and thus to remove interlaboratory differences. Using these advances, we predict melt viscosity solely with the use of Raman spectral measurements of multicomponent silicate glasses, thus demonstrating the potential of the method in describing physical properties of silicate melts.

An Avramov-based viscosity model for the SiO2-Al2O3-Na2O-K2O system in a wide temperature range

Abstract A modified Avramov equation is employed to describe the viscosity of silicate melts in the SiO2-Al2O3-Na2O-K2O system and its subsystems with associate species obtained from thermodynamic description and used as structural units. Two modifications to the Avramov equation are proposed: i) a stronger dependence of viscosity input of each structural unit on its concentration ii) the “fragility” parameter dependent on the melt composition at a given point. The model describes the viscosity reasonably well for most of the experimental data in the wide compositional range and in a temperature range from fully liquid to supercooled melts. Approaches to further improve the model are discussed.

Chiral Proportions of Nepheline Originating from Low-Viscosity Alkaline Melts. A Pilot Study

Chromatographic interaction between infiltrating solutions of racemic mixtures of enantiomers and enantiomorphic minerals with chiral excess has been proposed as a scenario for the emergence of biomolecular homochirality. Enantiomer separation is supposed to be produced by different partition coefficients of both enantiomers with regard to crystal faces or walls of capillary tubes in the enantiomorphic mineral. Besides quartz, nepheline is the only common magmatic mineral with enantiomorphic symmetry. It crystallizes from SiO2-undersaturated melts with low viscosity and is a promising candidate for chiral enrichment by autocatalytic secondary nucleation. Under liquidus conditions, the dynamic viscosity of silicate melts is mainly a function of polymerization. Melts with low concentrations of SiO2 (<55 wt%) and rather high concentrations of Na2O (>7 wt%) are only slightly polymerized and hence are characterized by low viscosities. Such melts can ascend, intrude or extrude by turbulent flow. Fourteen volcanic and subvolcanic samples from alkaline provinces in Africa and Sweden were chemically analyzed. Polished thin sections containing fresh nepheline phenocrysts were etched with 1% hydrofluoric acid at 20 °C for 15 to 25 min. Nepheline crystals suitable for a statistical evaluation of their etch figures were found in four samples. Crystals with chiral etch figures are mainly not twinned. Their chiral proportions in grain percentages of single crystals are close to parity in three samples. Only one sample shows a slight chiral excess (41.67% L-type vs. 58.33% D-type) but at a low level of significance (15 vs. 21 crystals, respectively).

Towards a structural model for the viscosity of geological melts

The viscosity of silicate melts is the most important physical property governing magma transport and eruption dynamics. This macroscopic property is controlled by composition and temperature but ultimately reflects the structural organization of the melt operating at the microscale. At present, there is no explicit relationship connecting viscosity to silicate melt structure and vice versa. Here, we use a single Raman spectroscopic parameter, indicative of melt structure, to accurately forecast the viscosity of natural, multicomponent silicate melts from spectroscopic measurements on glasses preserved on Earth and other planets. The Raman parameter is taken as the ratio of low and high frequency vibrational bands from the silicate glass by employing a green source laser wavelength of 514.5 nm (R514.5). Our model is based on an empirical linkage between R514.5 and coefficients in the Vogel–Fulcher–Tammann function for the temperature dependence of melt viscosity. The calibration of the Raman-based model for melt viscosity is based on 413 high-temperature measurements of viscosity on 23 melt compositions for which published Raman spectra are available. The empirical model obviates the need for chemical measurement of glass compositions, thereby, providing new opportunities for tracking physical and thermochemical properties of melts during igneous processes (e.g., differentiation, mixing, assimilation). Furthermore, our model serves as a milepost for the future use of Raman spectral data for predicting transport (and calorimetric) properties of natural melts at geological conditions (e.g., volatiles and pressure) and production.

Non-Newtonian behavior of solid-bearing silicate melts: An experimental study

The non-Newtonian behavior and its mechanism have not been clarified for the solid-bearing silicate melts, leading to difficulties and even errors in estimating silicate melt viscosity. In this study, a typical metallurgical slag was employed as a model system of solid-bearing silicate melt. The flow behavior of the slag was measured via a rotational type rheometer at various shear rates. The results demonstrate that the slags exhibit non-Newtonian behavior for solid fractions exceeding a critical value (Φc, i.e. 0.33–0.40 for the investigated samples), at which an abrupt viscosity increase occurs. Shear thinning (the viscosity decreases with increasing shear rate), thixotropy (a time-dependent shear thinning) and an apparent yield stress of 0.2–74.4 Pa for the investigated samples are the non-Newtonian characteristics observed in this study. The higher the solid fraction, the more pronounced the shear thinning. The shear thinning is mainly attributed to the disruption of crystal clusters. Thixotropic behavior is found to be caused by the irreversible microstructural evolution within the experimental time scale. The apparent yield stress is mainly due to the formation of a solid network and is increased with increasing the solid fraction.

Towards the reconciliation of viscosity change and CO2-induced polymerization in silicate melts

Deep mantle melts contain massive amounts of CO2 but three critical issues related to the effect of CO2 on molecular structure and physical properties of magmatic melts remain poorly constrained: 1) there is no exact picture of CO2 dissolution mechanism in silicate melt, 2) the silicate melt polymerization upon CO2 dissolution has not been reliably quantified and 3) the effect of CO2 on silicate melt viscosity has never been measured adequately.We synthesized a series of 17O and 29Si-enriched CO2-bearing melilitite (SiO2~35wt%) silicate glasses at high temperature and pressure. Using NMR spectroscopy, we have interrogated both anionic and cationic networks for quantifying the change in the degree of polymerization associated to CO2 incorporation in the melt. Increasing CO2 content induces a strong increase in the degree of polymerization. CO2 dissolution follows a complex mechanism involving the formation of Free Ionic Carbonate (FIC) Ca2+·CO32– species. This carbonate subnetwork is the precursor to the immiscibility process between a carbonate liquid and a silicate liquid.Glass transition temperature (Tg) measurements show that increasing CO2 content induces a decrease in Tg implying a decrease in viscosity for the studied low silica melt composition. This result appears in complete contradiction with the melt polymerization induced by CO2 as quantified by NMR. We propose a model that reconciles both aspects. CO2 induces silicate subnetwork polymerization resulting in a viscosity increase but it also induces a competing effect by forming a carbonate subnetwork having a low viscosity. The overall result appears dominated by the carbonate subnetwork resulting in a slight decrease in melt viscosity in agreement with existing studies.

Molecular structure, configurational entropy and viscosity of silicate melts: Link through the Adam and Gibbs theory of viscous flow

The Adam and Gibbs theory depicts the viscous flow of silicate melts as governed by the cooperative re-arrangement of molecular sub-systems. Considering that such subsystems involve the silicate Qn units (n=number of bridging oxygens), this study presents a model that links the Qn unit fractions to the melt configurational entropy at the glass transition temperature Tg, Sconf(Tg), and finally, to its viscosity η. With 13 adjustable parameters, the model reproduces η and Tg of melts in the Na2O-K2O-SiO2 system (60≤[SiO2]≤100mol%) with 1σ standard deviations of 0.18 log unit and 10.6°, respectively.The model helps understanding the links between the melt chemical composition, structure, Sconf and η. For instance, small compositional changes in highly polymerized melts generate important changes in their Sconf(Tg) because of an excess of entropy generated by mixing Si between Q4 and Q3 units. Changing the melt silica concentration affects the Qn unit distribution, this resulting in non-linear changes in the topological contribution to Sconf(Tg). The model also indicates that, at [SiO2]≥60mol%, the mixed alkali effect has negligible impact on the silicate glass Qn unit distribution, as corroborated by Raman spectroscopy data on mixed Na-K tri- and tetrasilicate glasses. Such model may be critical to link the melt structure to its physical and thermodynamic properties, but its refinement requires further high-quality quantitative structural data on silicate and aluminosilicate melts.

Modelling configurational entropy of silicate melts

The Adam-Gibbs theory provides a robust connection between the transport or relaxation properties of melts and their thermochemical properties. In its expanded form:logη=A+BTScTg+CpclnTTgthe equation has adjustable unknown parameters A, B and Sc (Tg) which can be estimated from experimental estimates of configurational heat capacity (Cpc), glass transition temperature (Tg) and viscosity (η). Here, we use recently published datasets for anhydrous and hydrous silicate melts and glasses (N~50) for which there are measurements of log η and calorimetric measurements of Cpc and Tg. Our fitting strategy follows the approach developed by previous workers with the sole exception that we assume all silicate melts converge to a common, but unknown, high temperature limit to melt viscosity (e.g., A=log η∞). Our optimal value for A is −3.51±0.25. A consequence of a common, high-temperature limit to silicate melt viscosity is that the corresponding model values of glass transition temperature (Tg12), melt fragility (m), and the ratio Cpc/Sc are constrained to lie on a single plane approximated as:CpcSc=−Tg12243399−m15.518+0.996thereby establishing a quantitative connection between calorimetric and rheological measurements. Lastly, we show a good correspondence between values of Tg12 and fragility (m) from this Adam-Gibbs based model of melt viscosity and values predicted by the GRD viscosity model for multicomponent silicate melts (cf. Giordano et al., 2008).

Differentiation of Vesta: Implications for a shallow magma ocean

The Dawn mission confirms earlier predictions that the asteroid 4 Vesta is differentiated with an iron-rich core, a silicate mantle and a basaltic crust, and supports the conjecture of Vesta being the parent body of the HED meteorites. To better understand its early evolution, we perform numerical calculations of the thermo-chemical evolution adopting new data obtained by the Dawn mission such as mass, bulk density and size of the asteroid.We have expanded the thermo-chemical evolution model of Neumann et al. (2012) that includes accretion, compaction, melting and the associated changes of the material properties and the partitioning of incompatible elements such as the radioactive heat sources, advective heat transport, and differentiation by porous flow, to further consider convection and the associated effective cooling in a potential magma ocean. Depending on the melt fraction, the heat transport by melt segregation is modelled either by assuming melt flow in a porous medium or by simulating vigorous convection and heat flux of a magma ocean with a high effective thermal conductivity.Our results show that partitioning of 26Al and its transport with the silicate melt is crucial for the formation of a global and deep magma ocean. Due to the enrichment of 26Al in the liquid phase and its accumulation in the sub-surface (for formation times t0<1.5 Ma), a thin shallow magma ocean with a thickness of 1 to a few tens of km forms – its thickness depends on the viscosity of silicate melt. The lifetime of the shallow magma ocean is O(104)–O(106) years and convection in this layer is accompanied by the extrusion of 26Al at the surface, resulting in the formation of a basaltic crust. The interior differentiates from the outside inwards with a mantle that is depleted in 26Al and core formation is completed within ∼0.3 Ma. The lower mantle experiences a maximal melt fraction of 45% suggesting a harzburgitic to dunitic composition. Our results support the formation of non-cumulate eucrites by the extrusion of early partial melt while cumulate eucrites and diogenites may form from the crystallising shallow magma ocean. Silicate melt is present in the mantle for up to 150 Ma, and convection in a crystallising core proceeds for approximately 100 Ma, supporting the idea of an early magnetic field to explain the remnant magnetisation observed in some HED meteorites.

Prediction of silicate melt viscosity from electrical conductivity: A model and its geophysical implications

AbstractOur knowledge of magma dynamics would be improved if geophysical data could be used to infer rheological constraints in melt‐bearing zones. Geophysical images of the Earth's interior provide frozen snapshots of a dynamical system. However, knowledge of a rheological parameter such as viscosity would constrain the time‐dependent dynamics of melt bearing zones. We propose a model that relates melt viscosity to electrical conductivity for naturally occurring melt compositions (including H2O) and temperature. Based on laboratory measurements of melt conductivity and viscosity, our model provides a rheological dimension to the interpretation of electromagnetic anomalies caused by melt and partially molten rocks (melt fraction ~ &gt;0.7).