U.S. Department of the Interior 

U.S. Geological Survey 

Techniques and Methods 5-D1 

SEM image of natura

hollow jarosite magn

approximately 3,500 
Methods for Synthesis of Some Jarosites

By Rhonda L. Driscoll and Reinhard W. Leinz

Techniques and Methods 5-D1

U.S. Department of the Interior

U.S. Geological Survey

Book 5—Laboratory Analysis

Section D—Geologic Analysis

Chapter 1
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2005

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Suggested citation: Driscoll, R.L., and Leinz, R.W., Methods for synthesis of some jarosites: U.S. Geological Survey 

Techniques and Methods 5-D1, 5 p.
iii

Contents

Abstract...........................................................................................................................................................1

Methods...........................................................................................................................................................1

Experimental Methods for Synthesis of End-Member K-Jarosite................................................1

Experimental Method for Synthesis of Mixed-Composition Jarosite .........................................1

Experimental Method for Synthesis of Natrojarosite .....................................................................2

Improved Experimental Method for Synthesis of Mixed-Composition Jarosite ........................2

Improved Experimental Method for Synthesis of End-Member Hydronium Jarosite ...............3

Improved Method for Synthesis of End-Member K-Jarosite ........................................................3

Low-Temperature Jarosite Synthesis ...............................................................................................3

Conclusion.......................................................................................................................................................5

References Cited............................................................................................................................................5

Tables

1. At-a-glance synthesis conditions for in-text numbered samples ........................................4

2. Yield results for low-temperature jarosite syntheses using different amounts

of KOH.............................................................................................................................................4
Abstract

Experimental procedures described in this report summarize attempts to synthesize potassium-, hydronium-, 

sodium-, and mixed-composition (hydronium-bearing) jarosites 

(KFe3(SO4)

2

(OH)6). For some experiments we duplicated or 

modified published synthesis methods; for others we designed 

new experiments. Initially, we were unable to predict ideal 

synthesis time and temperature conditions, product yields, or 

product composition. However, after experimentation, some 

acceptable combinations of chemical and physical factors were 

found to routinely synthesize chemically different jarosites. 

The mineralogical composition of synthetic substances was 

identified using a Shimadzu XRD 6000 instrument, Jade reduction software–Version 5, and ICDD Powder Diffraction Files–

Release 2002. The synthetic products were used as part of a 

characterization study of some natural and synthetic jarosites.

Methods

Experimental Methods for Synthesis of

End-Member K-Jarosite

The method of Baron and Palmer (1996) was used first 

to synthesize end-member K-jarosite; 17.2 g of ferric sulfate 

hydrate (Fe2(SO4)

3

·nH2O) and 5.6 g of potassium hydroxide 

(KOH) were dissolved in 100 mL 18MΩ water1. The solution was prepared in a covered glass beaker and placed on 

a 95°C stirring hot plate. A moderate boil was maintained 

for 4 hours; the solution was then removed from the stirring 

plate and the precipitate was allowed to settle. Once settling 

occurred, the liquid phase was carefully decanted and the 

precipitate was rinsed twice with deionized water. The rinsate 

was discarded and the solid remains were placed in a 110°C 

1

 Three grades of water are used in the laboratory: distilled water, deionized 

water, and 18MΩ, or ultra-pure water. Distilled water is water that has been 

heated and converted to steam and then cooled and condensed. The process 

concentrates dissolved solids that resist vaporization. Deionized water is 

water that is passed through a resin column to remove electrically charged, or 

ionized, dissolved particles. The ionized particles collect on the resin column. 

Most resin compositions are proprietary. 18MΩ, or ultra-pure water, is water 

that has been distilled, deionized, and passed through an activated carbon 

filtration system to remove trace bacteria and other impurities. 18MΩ water is 

a poor electricity conductor.

drying oven for 24 hours. After drying, the substance was 

collected and weighed; about 9 g of jarosite was produced 

(table 1, Sample 1). The product was analyzed using inductively coupled plasma–mass spectrometry (ICP-MS). ICP-MS 

analysis confirmed the presence of end-member K-jarosite 

(Desborough and others, 2004).

The synthesis was repeated using half as much KOH 

(2.80 g). Amounts of ferric sulfate hydrate and 18MΩ water 

were not changed. Heating method, temperature, time, and 

drying conditions were the same as those preceding. The 

second preparation yielded 7.7 g of a mixed-composition 

jarosite—K0.85H3O0.15Fe3(SO4)

2 ·(OH)6

—based on ICP-MS 

analysis of potassium (table 1, Sample 2).

Four additional preparations, using 17.2 g of ferric sulfate 

hydrate and 3.1, 2.6, 2.2, and 1.4 g of KOH, respectively, 

dissolved in 100 mL 18MΩ water, were prepared in the same 

way (table 1, Samples 3, 4, 5). Hydronium-bearing jarosites 

of different composition were produced.

The next synthesis required 17.2 g of ferric sulfate to be 

dissolved in 100 mL 18MΩ water. KOH was excluded. After 

heating and drying, the only mineral produced was a minute 

amount of schwertmannite (Fe3+

16O16(OH)12(SO4

)

2

), which was 

identified using X-ray diffraction (XRD).

The final preparation based on the Baron and Palmer 

(1996) method required dissolution of 6.56 g Fe2(SO4)

3 · nH2

O 

in 100 mL 18MΩ water. No other reagents were used. As in 

previous experiments, the solution was heated at 95°C for 4 

hours on a stirring hot plate. It was then allowed to cool for

2 hours, during which time it remained an amber liquid without any visible precipitate. The pH of this and the previous 

preparation liquid phase was less than 1. The pH of solution is 

significant because jarosite formation favors a pH range of 1.3 

to 3.5 (G.A. Desborough, oral commun., 2004).

Experimental Method for Synthesis of

Mixed-Composition Jarosite 

In this series of syntheses, preparations one and two made 

use of a goethite slurry. The slurry was made beforehand by 

(1) dissolving 25.0 g ferric nitrate (Fe(NO3)

3 · 9H2

O) in 412.5 

mL deionized water, (2) dissolving 28.0 g potassium hydroxide 

(KOH) in 200 mL deionized water to produce a 2.5N solution 

of KOH, and (3) adding 100 mL of the 2.5N KOH solution to 

the entire ferric nitrate solution and swirling to mix in a heatresistant Nalgene bottle. The mixture was then loosely capped 

Methods for Synthesis of Some Jarosites

By Rhonda L. Driscolland Reinhard W. Leinz
and placed in a drying oven, preheated to 60°C, for 24 hours. 

After the bottle was removed from the drying oven, the mixture 

was given time to cool at room temperature and to separate 

into distinct liquid and solid phases. After the liquid phase 

was decanted, the solid remains were washed with 500 mL 

deionized water, allowed to settle and separate, decanted, and 

rewashed overnight with 250 mL deionized water. An aliquot 

of the initial decant was reserved for pH measurement. The 

wash process was repeated for 6 consecutive days or until the 

pH of the decant solution measured 8.1. The final product had a 

watery consistency and was identified as goethite using XRD.

For the first synthesis in this series, 5.0 g of goethite 

slurry was mixed with 100 mL of 0.5N sulfuric acid (H2SO4). 

The mixture was heated in a glass beaker on a 95°C stirring 

plate for 3 hours. After the beaker was removed from the stirring plate, the liquid phase was decanted. The solid remains 

were placed in a 110°C drying oven for 18 hours. Prolonged 

drying produced a reddish-brown glutinous substance. Litmus 

paper indicated a highly acidic compound; XRD analysis identified a generic iron sulfate. 

The next synthesis in this series required dissolution 

of 16.0 g Fe2(SO4)3·nH2O in 100 mL 18MΩ water in a glass 

beaker; dissolution took about 3 minutes. Four grams of 

synthetic goethite slurry was then added, and the mixture was 

placed on a ≈75°C stirring plate. After 3 hours, the solution 

was transferred to a drying oven (preheated to 110°C) for 

48 hours. The dried product, when removed from the oven, 

resembled brittle, beige “taffy.” X-ray analysis indicated a 

generic ferric sulfate.

Experimental Method for Synthesis of 

Natrojarosite

The initial attempt to synthesize natrojarosite entailed 

dissolution of 17.2 g Fe2(SO4)

3

·nH2O and 4.0 g NaOH in 100 

mL 18MΩ water in a 250 mL glass beaker. The solution 

was brought to a slow boil on a stirring plate and left undisturbed for 4 hours. As in previous synthesis procedures, the 

solution was removed from the heat, decanted, rinsed with 

100 mL deionized water, and dried overnight at 100°C. The 

dried product, verified by XRD as end-member natrojarosite, 

weighed 20.7 g.

The synthesis was repeated using one-quarter as much 

NaOH (1.0 g). In all other ways, the second sodium preparation duplicated the first. Not surprisingly, the second preparation yielded less than one-quarter the amount of product, or 

2.3 g of natrojarosite. 

Improved Experimental Method for

Synthesis of Mixed-Composition Jarosite

For our next series of syntheses, we began with six 50 mL 

capped polypropylene tubes, each containing 2.8 g Fe2(SO4)

3

·

nH2O and 13 g 18MΩ water. The tubes were labeled I–VI. 

A specific weighed amount of 22.5 percent KOH solution was 

added to each tube:

Tube I 5.60 g KOH soln. Tube IV 0.46 g KOH soln.

Tube II 2.80 g KOH soln. Tube V 0.24 g KOH soln.

Tube III 1.40 g KOH soln. Tube VI 0.12 g KOH soln.

After the KOH solution was added, all tubes were shaken 

vigorously by hand. The content of each tube was then 

transferred to a corresponding Teflon bomb. Each bomb was 

sealed in a steel cylinder and placed in a furnace for 5 hours 

at 140°C. After removal from the furnace and a brief cooling 

interval, the six bombs were unsealed. The liquid from each 

bomb was decanted, and the solid remains were scraped from 

the Teflon vessel. The scrapings were washed with deionized water onto a Whatman #42 ashless filter paper molded 

inside a vacuum funnel. The funnel itself was fixed firmly 

over a vacuum flask. In this way most of the residual fluid 

was removed from the solid product with the product itself 

accumulating on the filter paper. The filter paper was then 

transferred to a drying oven. After 1 hour in the oven (60°C), 

five of the six syntheses yielded fine powders. The composition of the powders, using both standard XRD identification 

and a computer-based cell-refinement routine, was verified as 

hydronium-bearing jarosite. Yields were proportionate to the 

amount of KOH present in each solution:

Tube II 1.84 g Tube V 0.69 g

Tube III 1.32 g Tube VI 0.53 g.

Tube IV 1.19 g 

Preparation I failed to produce jarosite.

To determine the roles of time and temperature in jarosite 

formation, we again dissolved varying amounts of 22.5 percent 

KOH reagent in a fixed ferric sulfate hydrate solution (2.58 g 

Fe2(SO4)

3

·nH2O dissolved in 13 g 18MΩ water):

Tube I 1.870 g KOH soln. Tube IV 0.240 g KOH soln. 

Tube II 0.939 g KOH soln. Tube V 0.120 g KOH soln.

Tube III 0.467 g KOH soln. 

Sealed inside their own Teflon vessel, each mixture was 

heated for 4 hours at 100°C—a reduction of time and temperature of 1 hour and 40°C, respectively. These deliberate 

changes in synthesis conditions did not affect product composition (hydronium-bearing jarosite was confirmed by X-ray 

analysis), but did affect product mass:

Tube I 0.98 g Tube IV 0.45 g

Tube II 0.71 g Tube V 0.30 g.

Tube III 0.59 g

Because of the reduction of time and temperature of 

reaction, some of the reagent remained in solution, limiting the 

product mass. As the quantities of these syntheses were small, 

we did not use these materials for chemical studies.

 Methods for Synthesis of Some Jarosites
Improved Experimental Method for Synthesis of 

End-Member Hydronium Jarosite

One of our earliest syntheses was intended to produce 

hydronium jarosite. By combining Fe2(SO4)

3

·nH2O and water 

only, we hoped to synthesize a hydronium end-member. The 

experiment, conducted in a covered glass beaker on a hot 

plate, produced only a trace amount of schwertmannite. We 

reconsidered the synthesis and subsequently modified it by 

replacing the beaker and hot plate with a 200 mL Teflon bomb 

and furnace.

The first of the modified synthesis trials required dissolution of 20 g of ferric sulfate hydrate in a glass beaker containing 150 mL 18MΩ water. The ferric solution was poured 

into a large Teflon vessel, which was sealed inside a heavy 

steel canister. The Teflon bomb was heated for 5 hours in a 

140°C furnace. After removal from the furnace, the bomb 

was allowed to cool at room temperature for 2 hours. The 

solid phase was then extracted from the bomb and dried for 

1 hour in a 60°C oven. A scant 0.16 g of hydronium jarosite 

was recovered. A second, identical bomb synthesis yielded 

1.02 g of hydronium jarosite. The significant difference in 

yields was attributed to an unreliable temperature control on 

the furnace used to heat the first solution. Because hydronium 

jarosite was unmistakably identified using XRD, we were able 

to “mass produce” this desirable end-member following our 

modified method. In all, we made 13.5 g of H3O-jarosite with 

an average 0.83 g of product per synthesis.

Improved Method for Synthesis of

End-Member K-Jarosite

Of the many Teflon bomb syntheses conducted, we 

recorded negligible fluid loss during heating. Whether initiating the synthesis with 15 mL or 150 mL of solution, we 

consistently decanted the same liquid volume after heating. 

The only exception to this trend occurred during production of 

K-jarosite.

The K-jarosite solution was prepared by dissolving 25.8 

g Fe2(SO4)

3

·nH2O in a 250 mL glass beaker containing 130 

mL 18MΩ water. Next, 18.7 g of 45 percent KOH solution 

was added and mixed thoroughly by hand shaking. Additional 

18MΩ water was added to bring the solution to 150 mL. Following transfer to a 200 mL Teflon bomb, the solution was 

placed in a furnace and heated for 5 hours at 140°C. After 

cooling at room temperature, the liquid phase was decanted 

into a graduated cylinder. For the first time, fluid loss was 

measurable. Approximately 50 mL had been lost or consumed 

during heating. The solid phase was also atypical. After 

drying overnight in a 60°C oven, the solid had separated into 

discrete yellow and red layers. The yield, too, was unexpected—an impressive 16.33 g (table 1, Sample 6).

The entire experiment was performed a second time with 

near-identical results—a 50 mL fluid loss after heating, color 

separation during prolonged low-temperature drying, and 

recovery of 16.29 g of product (table 1, Sample 7).

These two syntheses produced a near-end-member 

jarosite (97 mol. percent K) and a hydronium-bearing jarosite 

(86 mol. percent K), respectively.

Low-Temperature Jarosite Synthesis

To determine if end-members K-jarosite and hydroniumjarosite mix in a straight line at known quantity intervals, we 

conducted a final series of syntheses. All products from this 

series were systematically X-rayed and plotted.

The first synthesis called for 17.2 g Fe2(SO4)

3

·nH2O, 100 

mL 18MΩ water, and 5.6 g KOH. The mixture was heated in 

a loosely covered glass beaker on a magnetic stirring hot plate. 

Hot plate temperature was set at 95°C. Heating time was 3 

hours. After removal from the stirring hot plate, the beaker 

was placed inside a preheated drying oven for 12 hours. Drying temperature was 60°C.

The second and third synthesis attempts required 17.2 g 

ferric sulfate hydrate, 100 mL 18MΩ water, and 2.8 g KOH 

and 1.4 g KOH, respectively. Each solution was mixed in a 

glass beaker, heated on a 95°C stirring hot plate for 3 hours, 

and dried for 12 hours at a constant temperature of 60°C.

The dried product of the first synthesis appeared as a 

fluffy pale-orange solid topped by a fine white crust. The 

products of the second and third syntheses were brittle and 

dark orange in color. All products were identified by XRD as 

something other than jarosite.

The next low-temperature synthesis series was performed 

in a closed system. The first of the series combined 5.6 g 

KOH with 17.2 g ferric sulfate hydrate and 100 mL 18MΩ

water. After stirring to dissolve and mix reagents, the solution 

was poured into a Teflon bomb and sealed inside a thickwalled steel canister. The canister was placed in a furnace 

preheated to 95°C. After heating for 3 hours, the canister 

was removed from the furnace and allowed to cool at room 

temperature for one-half hour. When the internal Teflon bomb 

was opened, its liquid content was poured through a Whatman 

#2 ashless filter paper. A fine-grained brick-red solid accumulated on the filter paper. The solid was rinsed with deionized water to remove residual acid. A yellow-orange solid 

was then scraped from the bottom and sidewalls of the Teflon 

vessel, washed onto another #2 ashless filter paper, and rinsed 

thoroughly with deionized water. The filter papers containing 

both the red and yellow-orange solids were placed on watch 

glasses and moved into a 60°C drying oven for 1 hour. Each 

dried solid phase weighed 3.5 g (table 1, Sample 8; table 2, 

products details).

The synthesis was repeated using decreasing amounts of 

KOH: 2.8 g, 1.4 g, 0.7 g, and 0.3 g (table 1, Samples 9, 10, 

11, 12; table 2, products details). The amount of iron (III) 

sulfate and the volume of 18MΩ water were unchanged for 

each synthesis. Furnace and oven temperatures and heating 

and drying times were also constant.

Methods 
Table 1. At-a-glance synthesis conditions for in-text numbered samples.

[Mol percent K determined by ICP-MS]

Sample number 

(beaker, stirring 

hot plate)

(Fe2(SO4)

3

•nH2O) (g) KOH 

(g) 18MΩ water (mL) Heating time and temperature Drying time and temperature mol % K

1 17.2 5.6 100 95°C/4 hours 110°C/24 hours 1

2 17.2 3.1 100 95°C/4 hours 110°C/24 hours 0.88

3 17.2 2.8 100 95°C/4 hours 110°C/24 hours 0.85

4 17.2 2.6 100 95°C/4 hours 110°C/24 hours 0.86

5 17.2 1.4 100 95°C/4 hours 110°C/24 hours 0.76

Sample number 

(Teflon bomb, 

furnace)

45% 

KOH 

soln. 

(g)

6 25.8 18.7 ≈130 140°C/5 hours 60°C/18 hours 0.97

7 25.8 18.7 ≈130 140°C/5 hours 60°C/24 hours 0.86

Sample number 

(Teflon bomb, 

furnace)

KOH 

(g)

8 17.2 5.6 100 95°C/3 hours 60°C/1 hour 0.91

9 17.2 2.8 100 95°C/3 hours 60°C/1 hour 0.85

10 17.2 1.4 100 95°C/3 hours 60°C/1 hour 1.76

11 17.2 0.7 100 95°C/3 hours 60°C/1 hour 0.73

12 17.2 0.3 100 95°C/3 hours 60°C/1 hour 0.71

Table 2. Yield results for low-temperature jarosite syntheses using different amounts of KOH.

[The fine products accumulated on the filter paper during initial decant. The coarse products were scraped off the sidewalls and bottom of the Teflon vessel used 

in the preparation. Both products were washed thoroughly with deionized water prior to drying]

 Amount of KOH1 Yield 1 Yield 2 Type jarosite 

(8) 5.6 g 3.5 g 

fine brick-red solid

3.5 g

coarse yellow-orange solid Both mixed composition

(9) 2.8 g 1.5 g

fine dark red

3.0 g

coarse dark yellow Both mixed composition

(10) 1.4 g 1.5 g

fine dark yellow

2.5 g

coarse light brown Both mixed composition

(11) 0.7 g 2.0 g 

fine dark yellow Single mixed composition

(12) 0.3 g 0.7 g

fine light yellow Single mixed composition

 1Numbers in parentheses added to correspond to entries in table 1.

   Methods for Synthesis of Some Jarosites
The entire synthesis was repeated a second time. Identical decreasing amounts of KOH were added to the same mixture of ferric sulfate hydrate (17.2 g) and 18MΩ water (100 

mL). Each solution was heated for 3 hours at 95°C, cooled for 

one-half hour, decanted through a #2 ashless filter paper, and 

dried for 1 hour in a preheated 60°C drying oven. The results 

of the duplicate synthesis were somewhat different from those 

of the first closed system series: product weights and compositions were comparable, but the color banding and fine-coarse 

distinctions did not occur—all products were uniformly fine 

grained and light yellow in color.

We are unaware of any furnace or drying oven temperature fluctuations or any reagent contamination. Heating and 

drying intervals were precisely timed. All reagents were 

weighed on the same toploading digital balance. Balance 

accuracy was verified prior to use. All glassware was prewashed with a cleanroom general purpose detergent, and all 

possible sources of cross contamination were removed from 

the work space. How then could the product of each duplicate 

synthesis differ in quality? At present this question is under 

investigation.

The type of jarosite for all the duplicate series syntheses 

was determined to be hydronium-bearing-jarosite.

Conclusion

Only after months of experimentation were we able 

to synthesize four distinct species of jarosite in significant 

quantities—end-members K-jarosite, hydronium jarosite and 

sodium jarosite, and variable mixed-composition jarosite. 

In addition, we were able to demonstrate that jarosite forms 

under very specific chemical and physical conditions in the 

laboratory. Those conditions include ratios of iron, sulfur, 

sodium, and potassium to water; synthesis temperature and 

time; and especially acidity of the formation environment. 

An open system, such as that involving use of a glass beaker 

and magnetic stirring hot plate, permits fluid loss. Fluid loss, 

in turn, whether through evaporation or some other means, 

affects the pH of solution. Jarosite, we now know, forms in a 

narrow pH range. A closed system eliminates the probability 

of fluid loss. Jarosite synthesis requires a stable fluid volume 

at a controlled pH. 

References Cited

Baron, Dirk, and Palmer, C.D., 1996, Solubility of jarosite at 

4°–35° C: Geochimica et Cosmochimica Acta, v. 60, no. 2, 

p. 185–195. 

Desborough, G.A., Smith, K.S., Swayze, G.A., Diehl, S.F., 

Lowers, H.A., Hammarstrom, J.M., Driscoll, R.L., and 

Leinz, R.W., 2004, A detailed comparison of natural and 

synthetic jarosite minerals: Geological Society of America 

Abstracts with Programs, v. 36, no. 5, p. 337.

References Cited