Where it forms, where it's found
- Geological setting
Oxidation zone of a complex polymetallic hydrothermal deposit.
- Type locality
- Keystone Mine
- Magnolia Mining District
- Boulder County
- Colorado
- USA
39.9886°, -105.3678°
4recorded occurrences
Physical
- Transparency
- Translucent
- Colour
- Golden yellow
- Streak
- Pale yellow-green
- Density
- 4.4 g/cm³
Optical
- Optical type
- Uniaxial (+)
- Refractive index
- 1.85 – 1.99
- Surface relief
- Very high
- Principal indices
- nω 1.85 · nε 1.99
Δ = 0Δmax
PPLpleochroism per grain
XPLindependent extinctions · rotate the stage
PPLpleochroism only · colour blends on rotation
XPLinterference colour · extinct every 90°
Retardation1400 nm
Order3rd order
XPL colour
Crystallography
- Space group
- #104
- Cell parameters
- a = 9.3667(5) Å · c = 7.6173(3) Å
- Unit cell volume
- 578.77 ų
- Z
- 2
- Morphology
Acicular hexagonal crystals, parallel aggregates and radiating sprays.
Crystal structure
Chemical composition
Synonyms
- Ferrotellurite
- IMA1987-049
- Keystoneiet
- Keystoneite (of Back et al.)
- Keystonite
In other languages
- German
- IMA 1987-049 · Keystoneit
- Italian
- keystoneite
- Portuguese
- IMA1987-049 · Keystoneíta
Classification
Strunz
10th ed.4.JM.05
- 4OxidesClass
- 4.JArsenites, antimonites, bismuthites, sulfites, selenites, tellurites; iodatesDivision
- 4.JMTellurites without additional anions, with H2OGroup
- 4.JM.05KeystoneiteSpecies
Dana
8th ed.34.03.02.03
- 34Selenites, Tellurites and SulfitesClass
- 34.03A2(XO3)3·xH2OType
- 34.03.02Zemannite GroupGroup
- 34.03.02.03KeystoneiteSpecies
CIM
—28.3.28
- 28Selenites, Selenates, Tellurites, and TelluratesClass
- 28.3TelluritesGroup
- 28.3.28KeystoneiteSpecies
Group, growth & confusion
Literature, links & citation
Citations
- 1988Back, M.E., Roberts, A.C., LePage, Y., Mandarino, J.A. (1988): Keystoneite, a new tellurite from the Keystone mine, Colorado, U.S.A. Joint Meeting Geological Association of Canada – Mineralogical Association of Canada, Program and Abstracts, 13, A4.
- 1995Miletich, Ronald (1995) Crystal chemistry of the microporous tellurite minerals zemannite and kinichilite, Mg0.5[Me2+Fe3+(TeO3)3]-4.5H2O, (Me2+=Zn;Mn). European Journal of Mineralogy, 7 (3). 509-524 doi:10.1127/ejm/7/3/0509DOI: 10.1127/ejm/7/3/0509
- 2005(2005) Keystoneite. Handbook of Mineralogy. Mineralogical Society of America
- 2021Missen, O. P., Back, M. E., Mills, S. J., Roberts, A. C., LePage, Y., Pinch, W. W., & Mandarino, J. A. (2021). Crystal Chemistry of Zemannite-Type Structures: III. Keystoneite, the Ni2+-Analogue of Zemannite, and Ferrotellurite Discredited. The Canadian Mineralogist, 59(2), 355-364.
Cite this entry
@misc{mineral2026,
author = {Mineral Index editorial board},
title = {Keystoneite — Mineral Index},
year = {2026},
url = {https://mineralindex.org/minerals/keystoneite-2192},
note = {Accessed 2026-05-11}
}