Where it forms, where it's found
- Geological setting
Reddish dolomite vein in hornfels.
- Type locality
- Jáchymov
- Karlovy Vary District
- Karlovy Vary Region
- Czech Republic
50.3661°, 12.9233°
3recorded occurrences
Physical
- Hardness
- 1Talc
- 2Gypsum
- 3Calcite
- 4Fluorite
- 5Apatite
- 6Orthoclase
- 7Quartz
- 8Topaz
- 9Corundum
- 10Diamond
- Transparency
- Transparent
- Colour
- colourless · snow-white · colourless in transmitted light.
- Cleavage
- Distinct/Good
On (010), distinct.
- Density
- 2.92 g/cm³
Optical
- Optical type
- Biaxial (+) · 2V calc = 54°
- Refractive index
- 1.565 – 1.58
- Surface relief
- Moderate
- Principal indices
- nα 1.565 · nβ 1.568 · nγ 1.580
- Dispersion
- r > v strong
Δ = 0Δmax
PPLpleochroism per grain
XPLindependent extinctions · rotate the stage
PPLpleochroism only · colour blends on rotation
XPLinterference colour · extinct every 90°
Retardation150 nm
Order1st order
XPL colour
Crystallography
- Morphology
Crystals minute, dull, prismatic [001]; also occurs as cotton-like fibers.
- Type-locality form
Transparent crystals, to 4 cm in length, partly altered to a milky colored material.
- Comment
inferred from optical data
Chemical composition
Synonyms
- Isoclasiet
- Isoclasit
In other languages
- German
- Isoklas
- Italian
- Isoclasite
Classification
Strunz
10th ed.8.DN.10
- 8Phosphates, Arsenates, VanadatesClass
- 8.DPhosphates, etc. with additional anions, with H2ODivision
- 8.DNWith only large cationsGroup
- 8.DN.10IsoclasiteSpecies
Dana
8th ed.42.06.02.01
- 42Hydrated Phosphates, Etc.containing Hydroxyl or HalogenClass
- 42.06A2(XO4)Zq·xH2OType
- 42.06.02— unnamed intermediate level —Group
- 42.06.02.01IsoclasiteSpecies
CIM
—19.4.4
- 19PhosphatesClass
- 19.4Phosphates of CaGroup
- 19.4.4IsoclasiteSpecies
Literature, links & citation
Citations
- 1870Sandberger, F., (1870): "Ueber Isoklas und Kollophan, zwei neue Phosphate": J. prakt Chemie, Neue Folge, 2,125-130 (as Isoklas).
- 1870Sandberger, F., (1870): Neues Jahrbuch für Mineralogie, Geologie und Paleontologie, Heidelberg, Stuttgart: 306 (as Isoklas).
- 1892Dana, Edward Salisbury; Dana, James Dwight (1892) A System of Mineralogy (6th ed.). John Wiley & Sons, Inc.
- 1921Larsen, Esper S. (1921) The microscopic determination of the nonopaque minerals. Bulletin 679. US Geological Survey doi:10.3133/b679 DOI: 10.3133/b679
- 1997Journal of the Czech Geological Survey (1997): 42(4): 24-25, 118-119.
Cite this entry
@misc{mineral2026,
author = {Mineral Index editorial board},
title = {Isoclasite — Mineral Index},
year = {2026},
url = {https://mineralindex.org/minerals/isoclasite-2051},
note = {Accessed 2026-05-11}
}