Melanterite mineral
Melanterite is the monoclinic ferrous sulfate heptahydrate mineral, FeSO4·7H2O, grandfathered in the September 2026 IMA list. It is distinct from dissolved ferrous sulfate, other sulfate hydrates and ferric oxides. The accepted primary study assigns minor melanterite in a mixed solid from a nitrate/Fe(II) microcosm containing Comamonas strain HJ-2. This is a qualified culture-associated phase observation, not proof of metabolically necessary crystallization, pure-mineral production or iron recovery. The strain's species identification is unresolved.
Microbial & Biochemical Mechanisms (1)
Minor melanterite assigned in mixed solids from an HJ-2 iron microcosm
biomineralization
Microbial
The authors assign melanterite alongside goethite, lepidocrocite and hematite in precipitates from Fe(II), nitrate and HJ-2 cells. Microbial participation denotes the presence of cultured cells in this experiment; it does not establish that cells caused melanterite crystallization. Unreported solid preparation and lack of comparator XRD leave residual ferrous sulfate crystallization during processing unresolved.
Experimental Context & Analytical Limits:
Materials and Methods: HJ-2 was isolated from Hanjiang riparian sediment after FeS/oxygen gradient enrichment and LB purification. Log-phase LB-grown cells were centrifuged at 8000 g, 4 degrees C for 8 min, washed twice in 10 mM PIPES at pH 7 and resuspended. Experiments used 100 mL anaerobic glass bottles, 10 mM PIPES, nominal 5% inoculum and 30 degrees C; actual liquid volume, inoculum basis and cell density are not specified. Two parallel experiments per group and uninoculated controls are reported. Figure 2 uses FeSO4 and NaNO3; the reported initial Fe(II) and nitrate concentrations are each 3.64 mmol/L. XRD used a Bruker D8-FOCUS, but solid collection time, washing, drying, oxygen exposure and phase quantification method are not specified. The 144 h solution endpoint is not an established XRD collection time.
Materials and Methods: HJ-2 was isolated from Hanjiang riparian sediment after FeS/oxygen gradient enrichment and LB purification. Log-phase LB-grown cells were centrifuged at 8000 g, 4 degrees C for 8 min, washed twice in 10 mM PIPES at pH 7 and resuspended. Experiments used 100 mL anaerobic glass bottles, 10 mM PIPES, nominal 5% inoculum and 30 degrees C; actual liquid volume, inoculum basis and cell density are not specified. Two parallel experiments per group and uninoculated controls are reported. Figure 2 uses FeSO4 and NaNO3; the reported initial Fe(II) and nitrate concentrations are each 3.64 mmol/L. XRD used a Bruker D8-FOCUS, but solid collection time, washing, drying, oxygen exposure and phase quantification method are not specified. The 144 h solution endpoint is not an established XRD collection time.
Curated Evidence Points:
Partial
Source:
peng2023
Results section on Fe(II) oxidation coupled with nitrate reduction and supporting Figure S2 assign melanterite (reference PDF 01-0255) in a mixed diffraction pattern. The figure labels melanterite 13.35%, goethite 55.52%, lepidocrocite 15.35% and hematite 15.76%. No refinement details, uncertainty, internal standard or absolute phase-mass basis are given. These are source-reported phase labels, not a validated melanterite yield or isolated-product purity. The named mineral remains a provisional phase assignment in this experimental mixture.
Context_only
Source:
peng2023
Figure 2 and its results report Fe(II) declining from 3.64 to 0.84 mmol/L within 144 h with cells and nitrate, while the no-cell and no-nitrate comparators change little. These solution concentrations do not quantify conversion into melanterite. Supporting Figure S2 supplies no corresponding control-solid patterns. The claim that melanterite proves incorporation of Fe(II) into ferric precipitates is not established by assigning a separate ferrous sulfate phase. Figure 1 SEM/EDS demonstrates Fe-bearing material but cannot itself identify melanterite or its formation mechanism.
Partial
Source:
peng2023
Figure 3 and the nitrite experiment show Fe(II) consumption with nitrite both with and without cells, reaching the reported zero by 480 h. This preserves a substantial abiotic route in the coupled iron system and prevents attributing all Fe oxidation to a cellular enzyme. Methodology S1 and Tables S3-S7 are gene annotations, not expression, knockout or enzyme assays demonstrating melanterite formation. No closed iron mass balance, isolated melanterite recovery or industrial application is demonstrated.
Partial
Source:
peng2023
The main identification paragraph calls HJ-2 C. terrigena and claims 100% 16S similarity to NBRC 14951 (AB680720.1). Supporting Figure S1 instead labels that neighbor C. testosteroni and separates it from the plotted C. terrigena strains. The article reports CCTCC AB 2021274, but no independently resolved culture-deposit record is accepted here. HJ-2 is retained as the study strain without a species-level organism ID.
Context_only
Source:
genbank_hj2
The current MZ701937.1 record names Comamonas thiooxydans strain HJ-2, whereas the article names C. terrigena. This accession conflict remains unresolved; it does not license silently renaming the experimental strain.
Context_only
Source:
genbank_nbrc14951
AB680720.1 currently identifies Comamonas testosteroni NBRC 14951, agreeing with Figure S1 and conflicting with the main identification paragraph. A matching comparison-strain label does not resolve HJ-2's species assignment or establish any type-strain identity for it.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026; Melanterite row, PDF page 139, and definitions on pages 1-2. Fe(SO4)(H2O)6·H2O, status G, year 1850.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15) -
handbook: Handbook of Mineralogy. Melanterite, version 1 (2001-2005), complete one-page entry; ferrous sulfate heptahydrate, monoclinic P21/c.
https://handbookofmineralogy.org/pdfs/melanterite.pdf (accessed 2026-10-15) -
peng2023: Peng, R., Shen, J., Li, S. and Liu, H. (2023; online 2022). Sediment-isolated Comamonas terrigena strain HJ-2: a novel nitrate-dependent ferrous-oxidizing bacterium with multifunction on pollutant transformation. Letters in Applied Microbiology 76(1), ovac022. Complete publisher HTML, Figures 1-5, and official supporting DOCX with Methodology S1, Figures S1-S3 and Tables S1-S8 inspected.
https://academic.oup.com/lambio/article/76/1/ovac022/6953919 (accessed 2026-10-15) -
genbank_hj2: NCBI GenBank MZ701937.1, 16S rRNA sequence of strain HJ-2; current record names Comamonas thiooxydans, TaxId 363952, conflicting with the article's C. terrigena assignment. Sequence record inspected without treating its species label as a resolved experimental identity.
https://www.ncbi.nlm.nih.gov/nuccore/MZ701937.1 (accessed 2026-10-15) -
genbank_nbrc14951: NCBI GenBank AB680720.1, Comamonas testosteroni NBRC 14951, 16S rRNA sequence; this is the article's cited comparison accession, and agrees with the name in supporting Figure S1 rather than the main text.
https://www.ncbi.nlm.nih.gov/nuccore/AB680720.1 (accessed 2026-10-15)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-15T12:45:08Z |
codex (GPT-6; codex) | CREATE | Created melanterite from current mineral authorities and the complete HJ-2 original plus supplement, retaining provisional mixed-phase scope, unresolved crystallization causality and contradictory strain identification. |
Record source: data/records/melanterite.yaml